U.S. patent application number 16/002796 was filed with the patent office on 2018-12-13 for wood-based solar thermal devices, and methods for fabrication and use thereof.
The applicant listed for this patent is University of Maryland, College Park. Invention is credited to Chaoji CHEN, Amy GONG, Liangbing HU, Yudi KUANG, Tian LI, Yiju LI, He LIU, Mingwei ZHU.
Application Number | 20180356127 16/002796 |
Document ID | / |
Family ID | 64564045 |
Filed Date | 2018-12-13 |
United States Patent
Application |
20180356127 |
Kind Code |
A1 |
HU; Liangbing ; et
al. |
December 13, 2018 |
WOOD-BASED SOLAR THERMAL DEVICES, AND METHODS FOR FABRICATION AND
USE THEREOF
Abstract
Solar thermal devices are formed from a block of wood, where the
natural cell lumens of the wood form an interconnected network that
transports fluid or material therein. The block of wood can be
modified to increase absorption of solar radiation. Combining the
solar absorption effects with the natural transport network can be
used for various applications. In some embodiments, heating of the
modified block of wood by insolation can be used to evaporate a
fluid, for example, evaporating water for extraction, distillation,
or desalination. In other embodiments, heating of the modified
block of wood by insolation can be used to change transport
properties of a material to allow it to be transported in the
interconnected network, for example, heating crude oil to adsorb
the oil within the block of wood.
Inventors: |
HU; Liangbing; (Potomac,
MD) ; ZHU; Mingwei; (Nanjing, CN) ; LI;
Yiju; (Beijing, CN) ; CHEN; Chaoji;
(Hyattsville, MD) ; LI; Tian; (Silver Spring,
MD) ; LIU; He; (Nanjing, CN) ; GONG; Amy;
(Potomac, MD) ; KUANG; Yudi; (Greenbelt,
MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Maryland, College Park |
College Park |
MD |
US |
|
|
Family ID: |
64564045 |
Appl. No.: |
16/002796 |
Filed: |
June 7, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62517595 |
Jun 9, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B05D 7/06 20130101; B01D
17/042 20130101; Y02A 20/212 20180101; F24S 10/80 20180501; C02F
1/043 20130101; F24S 10/90 20180501; Y02A 20/142 20180101; B01D
1/0035 20130101; F24S 70/10 20180501; C02F 1/14 20130101; B01D
5/006 20130101; C02F 2103/08 20130101; B01D 1/0005 20130101; F04B
19/006 20130101; F04B 17/006 20130101; Y02E 10/44 20130101; F24S
10/95 20180501; Y02A 20/124 20180101; F04B 19/16 20130101 |
International
Class: |
F24S 10/80 20060101
F24S010/80; C02F 1/14 20060101 C02F001/14; C02F 1/04 20060101
C02F001/04; B01D 1/00 20060101 B01D001/00; B01D 5/00 20060101
B01D005/00; B05D 7/06 20060101 B05D007/06; F04B 19/00 20060101
F04B019/00; F24S 10/95 20060101 F24S010/95; F24S 10/90 20060101
F24S010/90 |
Claims
1. A solar thermal device comprising: a natural wood block having:
a first surface for receiving solar radiation thereon; a second
surface, opposite the first surface, for contacting fluid; an
internal fluidic transport network comprised of microstructures of
natural wood between the first and second surfaces; and a plurality
of artificial holes extending from the first surface to the second
surface; and a solar absorption layer on at least the first surface
of the natural wood block, wherein the natural wood block pumps
fluid from the second surface to the first surface by the internal
fluidic transport network via capillary action and/or
nano-cavitation effects, and fluid from the internal fluidic
transport network and/or from the first surface returns to the
second surface via the artificial holes.
2. The solar thermal device of claim 1, wherein each artificial
hole has a diameter of 100 .mu.m to 5 mm.
3. The solar thermal device of claim 1, wherein the fluid contains
salt, and the natural wood block is constructed such that a
salinity in the internal fluidic transport network is higher than a
salinity within the artificial holes during transport of the fluid
between the first and second surfaces.
4. The solar thermal device of claim 1, wherein the natural wood
block has cellulose-based lumen extending along a tree growth
direction that is substantially parallel to at least one of the
first and second surfaces, and the internal fluidic transport
network comprises spirals or pits between adjacent lumen.
5. The solar thermal device of claim 1, wherein the natural wood
block has cellulose-based lumen extending along a tree growth
direction that is at a non-zero angle with respect to at least one
of the first and second surfaces, and the internal fluidic
transport network comprises the lumen.
6. The solar thermal device of claim 1, wherein the solar
absorption layer comprises: a carbonized portion of the natural
wood block, or a coating of at least one of nanoparticles,
nanowires, graphene, graphene oxide, reduced graphene oxide,
graphite, single walled carbon nanotubes, double walled carbon
nanotubes, multiwalled carbon nanotubes, polyaniline, carbon black,
amorphous carbon, hard carbon, and soft carbon.
7. The solar thermal device of claim 6, wherein the nanoparticles
comprise plasmonic metallic nanoparticles.
8. The solar thermal device of claim 1, further comprising at least
one of: a concentrator that focus insolation onto the first
surface; a collector that collects vapor emanating from the first
surface; and a condenser that condenses vapor from the first
surface.
9. A solar thermal device comprising: a natural wood block having:
a first surface for receiving solar radiation thereon; a second
surface, opposite the first surface, for contacting fluid; and an
internal fluidic transport network comprised of microstructures of
natural wood between the first and second surfaces; and a solar
absorption layer on at least the first surface of the natural wood
block, wherein the natural wood block has cellulose-based lumen
extending along a tree growth direction that is substantially
parallel to at least one of the first and second surfaces, the
internal fluidic transport network comprises spirals or pits
between adjacent lumen, and the natural wood block pumps fluid from
the second surface to the first surface by the internal fluidic
transport network via capillary action and/or nano-cavitation
effects.
10. The solar thermal device of claim 9, wherein the solar thermal
device comprises at least one artificial hole extending from the
first surface to the second surface and having a diameter of 100
.mu.m to 5 mm.
11. The solar thermal device of claim 9, wherein the solar
absorption layer comprises: a carbonized portion of the natural
wood block, or a coating of at least one of nanoparticles,
nanowires, graphene, graphene oxide, reduced graphene oxide,
graphite, single walled carbon nanotubes, double walled carbon
nanotubes, multiwalled carbon nanotubes, polyaniline, carbon black,
amorphous carbon, hard carbon, and soft carbon.
12. The solar thermal device of claim 11, wherein the nanoparticles
comprise plasmonic metallic nanoparticles.
13. The solar thermal device of claim 9, further comprising at
least one of: a concentrator that focus insolation onto the first
surface; a collector that collects vapor emanating from the first
surface; and a condenser that condenses vapor from the first
surface.
14. A solar thermal device comprising: a carbonized block of
natural wood having: a first surface for receiving solar radiation
thereon; a second surface, opposite the first surface, for
contacting a material to be adsorbed; and an internal fluidic
transport network comprised of microstructures of the natural wood
between the first and second surfaces; wherein all internal and
external surfaces of the carbonized block have been carbonized, the
carbonized block has a porosity greater than that of the natural
wood, and the carbonized block is constructed to adsorb said
material into the internal fluidic transport network.
15. The solar thermal device of claim 14, wherein said surfaces of
the carbonized block are hydrophobic.
16. The solar thermal device of claim 14, wherein the carbonized
block has cellulose-based lumen extending along a tree growth
direction that is at a non-zero angle with respect to at least one
of the first and second surfaces, and the internal fluidic
transport network comprises the lumen.
17. The solar thermal device of claim 14, wherein the carbonized
block has cellulose-based lumen extending along a tree growth
direction that is substantially parallel to at least one of the
first and second surfaces, and the internal fluidic transport
network comprises spirals or pits between adjacent lumen.
18. The solar thermal device of claim 17, wherein the carbonized
block includes at least one artificial hole extending from the
first surface to the second surface, each artificial hole having a
diameter of 50 .mu.m to 500 .mu.m.
19. The solar thermal device of claim 14, wherein the greater
porosity includes pores introduced by at least one of: at least
partial delignification of the natural wood prior to carbonization
thereof; and CO.sub.2 activation during carbonization.
20. The solar thermal device of claim 14, further comprising a pump
that removes the adsorbed material from the from the carbonized
block.
21-39. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Application No. 62/517,595, filed Jun. 9, 2017, which is hereby
incorporated by reference herein in its entirety.
FIELD
[0002] The present disclosure relates generally to solar thermal
devices, and, more particularly, to solar thermal devices including
a wood-based substrate for fluid or material transport and/or
evaporation.
SUMMARY
[0003] In embodiments, a solar thermal device is formed from a wood
block. The naturally-occurring microstructure (e.g., cell lumen
such as vessels, fibers, and tracheids) of the wood block forms an
interconnected transport network that is used to passively
transport a fluid or material therein. The wood block can be
modified to increase absorption of radiation (e.g., insolation),
for example, by coating one or more surfaces of the wood block or
by modifying a surface layer (e.g., carbonization) of the wood
block. The absorbed radiation can heat the wood block (or a portion
thereof), which can alter a property of the fluid or material. For
example, the heated wood block can cause a phase change of the
fluid or material, or can alter a transport property of the fluid
or material.
[0004] In one or more embodiments, a solar thermal device comprises
a natural wood block and a solar absorption layer. The natural wood
block can have a first surface, a second surface, an internal
fluidic transport network, and a plurality of artificial holes. The
first surface can be for receiving solar radiation thereon, while
the second surface can be opposite the first surface and can be for
contacting fluid. The solar absorption layer can be at or on at
least the first surface of the natural wood block. The internal
fluidic transport network can be comprised of microstructures of
natural wood between the first and second surfaces. The natural
wood block can pump fluid from the second surface to the first
surface by the internal fluidic transport network via capillary
action and/or nano-cavitation effects. Fluid from the internal
fluidic transport network and/or from the first surface returns to
the second surface via the artificial holes.
[0005] In one or more embodiments, a solar thermal device comprises
a natural wood block and a solar absorption layer. The natural wood
block can have a first surface, a second surface, and an internal
fluidic transport network. The first surface can be for receiving
solar radiation thereon, while the second surface can be opposite
the first surface and can be for contacting fluid. The solar
absorption layer can be at or on at least the first surface of the
natural wood block. The internal fluidic transport network can be
comprised of microstructures of natural wood between the first and
second surfaces. The natural wood block can pump fluid from the
second surface to the first surface by the internal fluidic
transport network via capillary action and/or nano-cavitation
effects. The natural wood block has cellulose-based lumen extending
along a tree growth direction that is substantially parallel to at
least one of the first and second surfaces. The internal fluidic
transport network includes spirals or pits between adjacent
lumen.
[0006] In one or more embodiments, a solar thermal device comprises
a carbonized block of natural wood having a first surface, a second
surface, and an internal fluidic transport network. The first
surface can be for receiving solar radiation thereon, while the
second surface can be opposite the first surface and can be for
contacting a material to be adsorbed. The internal fluidic
transport network can be comprised of microstructures of the
natural wood between the first and second surfaces. All internal
and external surfaces of the carbonized block have been carbonized
such that a porosity of the carbonized block is greater than that
of the natural wood. The carbonized wood is constructed to adsorb
said material into the internal fluidic transport network.
[0007] In one or more embodiments, a method includes cutting a
block of natural wood to have a first surface, a second surface
opposite the first surface, and an internal fluidic transport
network comprised of microstructures of natural wood between the
first and second surfaces. The method can further include forming a
solar absorption layer on or from at least the first surface of the
natural wood block, and forming a plurality of artificial holes
extending from the first surface to the second surface.
[0008] In one or more embodiments, a method includes providing a
wood block having a first surface, a second surface opposite the
first surface, a solar absorption layer formed at the first
surface, and a fluidic transport network formed by microstructures
of natural wood between the first and second surfaces. The fluidic
transport network can further include at least one of a plurality
of natural lumens extending from the first surface to the second
surface and a plurality of artificial holes extending from the
first surface to the second surface. Each natural lumen can have a
diameter greater than or equal to 100 .mu.m, and each artificial
hole having a diameter of 100 .mu.m to 5 mm. The method can further
include placing the second surface of the natural wood block in
contact with a fluid, and then exposing the first surface to
insolation. The wood block can pump fluid from the second surface
to the first surface via capillary action and/or nano-cavitation
effects in the fluidic transport network, and fluid from the
fluidic transport network and/or from the first surface can return
to the second surface via the plurality of natural lumens and/or
artificial holes.
[0009] In one or more embodiments, a method includes providing a
carbonized block of natural wood having a first surface, a second
surface opposite the first surface, and an internal fluidic
transport network comprised of microstructures of the natural wood
between the first and second surfaces. The carbonized block can
have a porosity greater than that of the natural wood. The method
can further include placing the second surface of the carbonized
block in contact with a material to be adsorbed, and exposing the
first surface to insolation. During the exposing to insolation, the
carbonized block heats the material contacting the second surface
such that the material has a mobility greater than that of the
material prior to exposure to insolation. The carbonized block can
adsorb the heated material into the internal fluidic transport
network.
[0010] Objects and advantages of embodiments of the disclosed
subject matter will become apparent from the following description
when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Embodiments will hereinafter be described with reference to
the accompanying drawings, which have not necessarily been drawn to
scale. Where applicable, some features may not be illustrated to
assist in the illustration and description of underlying features.
Throughout the figures, like reference numerals denote like
elements.
[0012] FIG. 1A is a simplified schematic illustrating aspects of a
solar thermal setup employing a wood-based evaporator, according to
one or more embodiments of the disclosed subject matter.
[0013] FIG. 1B is a simplified schematic of an exemplary solar
thermal device with wood-based evaporator, according to one or more
embodiments of the disclosed subject matter.
[0014] FIG. 1C is a simplified schematic of another exemplary solar
thermal device with wood-based evaporator, according to one or more
embodiments of the disclosed subject matter.
[0015] FIG. 2A is a simplified illustration of a natural piece of
wood.
[0016] FIG. 2B is a scanning electron microscope (SEM) image of a
cross-section, in a direction perpendicular to tree growth, of
natural wood.
[0017] FIG. 3A is an SEM image of natural wood showing top and side
surfaces.
[0018] FIG. 3B is an SEM image of a longitudinal cross-section of
the natural wood of FIG. 3A, illustrating vessel lumen for fluid
transport and small pits that facilitate transport to neighboring
lumen.
[0019] FIG. 3C is an SEM image showing a detailed view of the cell
wall of a lumen of FIG. 3B, where aligned cellulose microfibrils
are embedded within lignocellulosic matrices.
[0020] FIG. 4A is a simplified schematic of a wood-based evaporator
in a horizontal cut configuration with a solar absorption layer,
according to one or more embodiments of the disclosed subject
matter.
[0021] FIG. 4B is a simplified schematic illustrating an evaporator
according to the structure of FIG. 4A, with a carbonized layer as
the solar absorption layer, according to one or more embodiments of
the disclosed subject matter.
[0022] FIG. 4C is an SEM image of the top carbonized surface of a
wood-based evaporator having the structure of FIG. 4B, according to
one or more embodiments of the disclosed subject matter.
[0023] FIG. 4D is an SEM image of a cross-section of the wood-based
evaporator of FIG. 4C showing the microstructure comprised of
vessels, fiber tracheids, and pits.
[0024] FIG. 5A is a graph of experimentally measured light
absorption spectra for the fabricated wood-based evaporator of FIG.
4C (bi-layer wood) as compared to amorphous carbon and natural
wood.
[0025] FIG. 5B is a graph of groundwater extraction performance of
the fabricated wood-based evaporator of FIG. 4C when placed in wet
sand.
[0026] FIG. 5C is a graph of enhancement factor for groundwater
extraction by the fabricated wood-based evaporator of FIG. 4C when
placed in wet sand.
[0027] FIG. 5D is a graph of solar steam generation efficiency at
different light intensities for groundwater extraction by the
fabricated wood-based evaporator of FIG. 4C when placed in wet
sand.
[0028] FIG. 5E is a graph of desalinated water extraction
performance of the fabricated wood-based evaporator of FIG. 4C when
placed in seawater.
[0029] FIG. 5F is a graph of enhancement factor for desalinated
water extraction by the fabricated wood-based evaporator of FIG. 4C
when placed in seawater.
[0030] FIG. 5G is a graph of solar steam generation efficiency at
different light intensities for desalinated water extraction by the
fabricated wood-based evaporator of FIG. 4C when placed in
seawater.
[0031] FIG. 5H is a graph comparing the solar steam generation
efficiency for pure water extraction by wood-based evaporators of
FIG. 4C fabricated using different types of wood.
[0032] FIG. 6A is a simplified schematic of a wood-based evaporator
in a horizontal cut configuration with particles coated on multiple
surfaces of the wood as the solar absorption layer, according to
one or more embodiments of the disclosed subject matter.
[0033] FIG. 6B is a simplified schematic illustrating a magnified
portion of an evaporator according to the structure of FIG. 6A,
with plasmonic nanoparticles, and illustrating water transport
along microchannels of the evaporator, according to one or more
embodiments of the disclosed subject matter.
[0034] FIG. 6C is a simplified schematic illustrating additional
aspects of a wood-based evaporator according to the structure of
FIG. 6B.
[0035] FIG. 6D is an SEM image of a top surface of a wood-based
evaporator having the structure of FIG. 6C.
[0036] FIG. 6E is an SEM image showing top and side surfaces of the
wood-based evaporator of FIG. 6D.
[0037] FIG. 6F is an SEM image of a longitudinal cross-section of
the wood-based evaporator of FIG. 6D, illustrating aligned
cellulose nanofibers.
[0038] FIG. 6G is a transmission electron microscope (TEM) image of
palladium (Pd) nanoparticles on a surface of a microchannel of the
wood-based evaporator of FIG. 6D.
[0039] FIG. 7A is a graph of experimentally measured light
absorption spectra for the fabricated wood-based evaporator of FIG.
6D (plasmonic wood) as compared to natural wood.
[0040] FIG. 7B is a graph of angle resolved absorption of the
fabricated wood-based evaporator of FIG. 6D as compared to natural
wood at a wavelength of 550 nm.
[0041] FIGS. 7C-7E are graphs of steam evaporation rate,
enhancement factor, and steam generation efficiency, respectively,
for the fabricated wood-based evaporator of FIG. 6D as a function
of different solar illumination intensities.
[0042] FIG. 8A is a simplified schematic diagram of a cross-section
of a wood-based evaporator, in a horizontal cut configuration,
employing a micro-sheet top surface, according to one or more
embodiments of the disclosed subject matter.
[0043] FIG. 8B is a simplified cutaway view of an individual cell
of a wood-based evaporator according to the structure of FIG. 8A,
employing a carbon nanotube (CNT) coating as the solar absorption
layer, according to one or more embodiments of the disclosed
subject matter.
[0044] FIG. 8C is a simplified isometric view illustrating
additional aspects of a wood-based evaporator according to the
structure of FIG. 8B.
[0045] FIG. 8D is a simplified magnified view illustrating the
structure of carbon-nanotube coating on microsheet surfaces of the
wood-based evaporator of FIG. 8C.
[0046] FIGS. 9A-9B are graphs of water extraction performance and
steam generation efficiency for a fabricated wood-based evaporator
having the structure of FIGS. 8B-8C.
[0047] FIG. 10A is a simplified schematic of a cross-section of a
wood-based evaporator, in a vertical cut configuration with a solar
absorption layer, according to one or more embodiments of the
disclosed subject matter.
[0048] FIG. 10B is a simplified cutaway view of a wood-based
evaporator according to the structure of FIG. 10A, employing
graphite as the solar absorption layer, according to one or more
embodiments of the disclosed subject matter.
[0049] FIG. 10C is an SEM image of a cross-section of a wood-based
evaporator fabricated according to structure of FIG. 10B, according
to one or more embodiments of the disclosed subject matter.
[0050] FIG. 10D is an SEM image of cross-section of vessel lumens
of FIG. 10C, illustrating the pits and spirals that facilitate
cross-plane transport of fluid.
[0051] FIG. 10E is a magnified SEM image of the pits and spirals of
FIG. 10D.
[0052] FIG. 10F is another SEM image of a wood-based evaporator
fabricated according to structure of FIG. 10B, according to one or
more embodiments of the disclosed subject matter.
[0053] FIG. 11A is a graph of thermal conductivity of dry wood
along (in-plane) and across (cross-plane) the tree growth
direction.
[0054] FIG. 11B is a graph of experimentally measured light
absorption spectra for the fabricated wood-based evaporator of FIG.
10B (graphite) as compared to uncoated natural wood.
[0055] FIG. 11C is a graph of evaporation rate as a function of
time for the fabricated wood-based evaporator of FIG. 10B during 1
sun illumination.
[0056] FIGS. 11D-11E are graphs of steam evaporation rate and steam
generation efficiency for the fabricated wood-based evaporator of
FIG. 10B as a function of different solar illumination
intensities.
[0057] FIG. 12A is a simplified illustration of a wood-based
evaporator according to FIG. 10A, employing carbonization of the
wood as the solar absorption layer, according to one or more
embodiments of the disclosed subject matter.
[0058] FIG. 12B is a close-up cutaway view of the wood-based
evaporator of FIG. 12A.
[0059] FIG. 12C is a graph of experimentally measured light
absorption spectra for a wood-based evaporator of FIG. 12A (C-L
Wood) as compared to uncoated natural wood having a vertical cut
(N-L Wood).
[0060] FIG. 12D is a graph of water evaporation rates and
efficiencies of a wood-based evaporator of FIG. 12A as a function
of different solar illumination intensities.
[0061] FIG. 13A is a simplified schematic of a wood-based
evaporator, in a horizontal cut configuration with a carbonized
layer as the solar absorption layer and naturally occurring pores
that prevent salt accumulation, according to one or more
embodiments of the disclosed subject matter.
[0062] FIG. 13B is a close-up illustration of xylem lumen and pores
of a wood-based evaporator according to FIG. 13A.
[0063] FIG. 13C is an SEM image of a top surface of a wood-based
evaporator fabricated according to the structure of FIG. 13A.
[0064] FIG. 13D is a close-up SEM image illustrating one of the
pores of the wood-based evaporator of FIG. 13C.
[0065] FIG. 14A is a graph of experimentally measured light
absorption spectra for the fabricated wood-based evaporator of FIG.
13C (bilayer wood) as compared to uncoated natural wood.
[0066] FIGS. 14B-14C are graphs of steam evaporation rate and steam
generation efficiency for the fabricated wood-based evaporator of
FIG. 13C as a function of different solar illumination
intensities.
[0067] FIG. 15A is a simplified schematic of a wood-based
evaporator, in a horizontal cut configuration with artificially
introduced holes that prevent salt accumulation, according to one
or more embodiments of the disclosed subject matter.
[0068] FIGS. 15B-15C are simplified cutaway and operational
illustrations of a wood-based evaporator according to the structure
of FIG. 15A, showing fluid recirculation features offered by
artificial holes, according to one or more embodiments of the
disclosed subject matter.
[0069] FIG. 15D is an image of a wood-based evaporator fabricated
according to the structure of FIG. 15B.
[0070] FIG. 15E is an SEM image of one of the artificial holes of
the wood-based evaporator of FIG. 15D.
[0071] FIG. 15F is an SEM image of a cross-section of one of the
artificial holes of the wood-based evaporator of FIG. 15D,
illustrating pits and spirals connecting to adjacent lumen.
[0072] FIG. 16A is a graph of steam generation efficiency for the
fabricated wood-based evaporator of FIG. 15D as a function of time,
as compared to natural wood.
[0073] FIG. 16B is a graph of steam generation efficiency for the
fabricated wood-based evaporator of FIG. 15D as a function of salt
concentration, as compared to a wood-based evaporator without
artificial holes.
[0074] FIG. 17 is a simplified schematic of a wood-based
evaporator, in a vertical cut configuration with artificial holes
that prevent salt accumulation, according to one or more
embodiments of the disclosed subject matter.
[0075] FIG. 18 is a process flow diagram for use of a wood-based
evaporator for fluid extraction, distillation, or desalination,
according to one or more embodiments of the disclosed subject
matter.
[0076] FIG. 19 is a process flow diagram for forming a wood-based
evaporator or solar thermal device including the wood-based
evaporator, according to one or more embodiments of the disclosed
subject matter.
[0077] FIG. 20A is a simplified schematic illustrating fabrication
of vertical cut wood-based evaporators by rotary cutting, according
to one or more embodiments of the disclosed subject matter.
[0078] FIG. 20B is an illustration of an exemplary manufacturing
process according to the generalized process of FIG. 20A.
[0079] FIG. 21A is a simplified schematic of a scalable assembly of
unit cells of wood-based evaporators, according to one or more
embodiments of the disclosed subject matter.
[0080] FIG. 21B is an image of a panel assembled from wood-based
evaporator unit cells according to the generalized configuration of
FIG. 21A.
[0081] FIG. 22A is a simplified schematic of a wood-based thermal
adsorber, in a horizontal cut configuration, according to one or
more embodiments of the disclosed subject matter.
[0082] FIG. 22B is a simplified operational illustration of an
exemplary thermal adsorber according to the generalized
configuration of FIG. 22A to remove crude oil from water.
[0083] FIGS. 23A-23D are images of different stages in removal of
crude oil from water using the wood-based thermal adsorber.
[0084] FIG. 24 is a simplified schematic of an exemplary solar
thermal device with wood-based adsorber and a pump for periodic or
continuous refreshing of the adsorber, according to one or more
embodiments of the disclosed subject matter.
[0085] FIG. 25 is a process flow diagram for use of a wood-based
adsorber for adsorption, according to one or more embodiments of
the disclosed subject matter.
[0086] FIG. 26 is a process flow diagram for forming a wood-based
adsorber or solar thermal device including the wood-based adsorber,
according to one or more embodiments of the disclosed subject
matter.
DETAILED DESCRIPTION
[0087] Embodiments of the disclosed subject matter provide solar
thermal devices formed from a block of natural wood. The natural
microchannels (i.e., cell lumen) within the wood are used to
transport fluid and/or a material within the block and/or between
exterior surfaces of the block. In various embodiments, the block
of natural wood can be modified to improve absorption of solar
radiation (i.e., insolation). For example, the block of natural
wood can include a solar absorptive coating on one or more of the
external surfaces, and/or can have a layer thereof that is modified
(e.g., by carbonization). Heating due to the absorbed solar
radiation can induce changes in the fluid/material, for example, to
cause a phase change (e.g., evaporation) or to improve a transport
property thereof (e.g., to allow the material to flow into the
block).
[0088] FIG. 1A illustrates generalized aspects of a solar thermal
setup 100, where a block of modified natural wood is used as an
evaporator 102. Wood-based evaporator 102 can be placed into
contact with a fluid source 110, which may be a body of the fluid
(e.g., ocean or lake) or a material containing the fluid (e.g.,
soil or sand). The modified natural wood block can interact with
fluid source 110 to draw a portion of fluid 112 into the wood
block, for example, by capillary effect in the
naturally-hydrophilic microchannels of the wood block.
[0089] Wood-based evaporator 102 can receive insolation 108 that
heats the fluid 112 in the evaporator 102 to generate vapor 114.
For example, optical system 104 can be provided to direct incident
insolation 106 to evaporator 102. In some embodiments, insolation
106 can be focused by optical system 104, such that the incident
radiation 108 on the evaporator 102 has an intensity greater than 1
sun. For example, the optical system 104 can include a
transmission-based concentrator (e.g., one or more lenses) and/or a
reflection-based concentrator (e.g., one or more mirrors). The
vapor 114 that emanates from the evaporator 102 can be collected by
collector 116 for further use. For example, the setup 100 can be
used to provide desalination or distillation of a fluid (e.g.,
water). In such configurations, the collector 116 can collect and
condense the vapor 114 in order to provide the desalinated or
distilled fluid.
[0090] FIG. 1B illustrates an example of a solar thermal system 120
based on the principles of FIG. 1A. Solar thermal system 120
includes a wood-based evaporator 122 disposed with a surface
thereof in contact with fluid source 110. An insulating housing 128
is coupled to the wood-based evaporator 122 and supports
optically-transmissive plate 124 above the evaporator 122. For
example, the optically-transmissive plate 124 can be a transparent
glass or plastic plate (i.e., no focusing) or a lens (e.g., Fresnel
lens) formed of glass or plastic (i.e., focusing). In this
configuration, the optically-transmissive plate 124 serves as both
input optical system 104 and a portion of collector 116. Thus,
fluid 112 is transported through the evaporator 122 where it is
heated proximal to an upper surface of the evaporator 112 by
incident solar radiation 106 to generate vapor 114. The vapor 114
collects on plate 124, where it condenses to form fluid drops 130.
The fluid drops 130 are directed by the effect of gravity along the
sloped surface of plate 124 to be collected by basin 132.
[0091] FIG. 1C illustrates another example of a solar thermal
system 140 based on the principles of FIG. 1A. Solar thermal system
140 includes a wood-based evaporator 142 disposed with a surface
thereof in contact with fluid source 110. A capture hood 144 can be
disposed over the evaporator 142 to capture the generated vapor
114. The capture hood 144 may be constructed to allow solar
radiation 106 to pass therethrough to evaporator 142. Optionally,
the capture hood 144 can include focusing optics to increase an
intensity of the radiation incident on an absorbing surface of the
evaporator 142. The captured vapor can be directed to a condenser
146 to convert the vapor back to a fluid, which can then be stored
in a container 148 for later or immediate use.
[0092] As noted above, transport of the fluid in the wood-based
evaporator 102 can be via the natural microchannels formed by cells
of the wood. Natural wood has a unique three-dimensional porous
structure 200 with multiple channels, including lumina 202
extending in a direction 206 of wood growth, as illustrated in
FIGS. 2A-2B. Cell walls 204 in the natural wood 200 are mainly
composed of cellulose, hemicellulose, and lignin, with the three
components intertwining with each other to form a strong and rigid
wall structure.
[0093] Wood can be divided into hardwood and softwood based on its
physical structure and composition. For example, hardwoods can
include balsa, bass, cocobolo, elm, locust, maple, oak, olive,
padauk, and poplar wood. For example, softwoods include cedar,
pine, and yew. Hardwood is formed of three kinds of cells--fiber
tracheids, vessel elements, and parenchyma. Vessels in hardwood
have a large lumen diameter and are connected by perforation plates
at the cell ends to function as the main pathways for water
transport. The fiber tracheids with a smaller lumen diameter are
interconnected through pits and mainly used for structural
support.
[0094] For example, FIGS. 3A-3B show vessels 302 and interstitial
tracheids 304, formed by respective cell walls, in block of wood
300, where the cell walls are formed of aligned cellulose
microfibrils embedded within a lignocellulosic matrix as shown in
FIG. 3C. As such, the hardwoods have two peaks in pore size
distribution corresponding to the fiber tracheid and vessel
diameters. In contrast, softwood is primarily formed of highly
elongated tracheids and parenchyma. The tracheids have the function
of providing mechanical support and transferring water via bordered
pits. As such, the softwoods exhibit a more homogenous pore size
distribution.
[0095] In spite of their structural differences, both hardwood and
softwood have inherent hierarchical structures, with
vertically-aligned microchannels for transporting water, ions, and
other nutrients. Moreover, the cellulose and hemicellulose contain
a large number of hydroxyl groups and are highly hydrophilic. Thus,
the composition of the wood yields hydrophilicity of the cell walls
and a similar overall structure of the wood block, regardless of
the wood species. The hydrophilic and porous structure of
evaporators formed by natural wood of either hardwood or softwood
can provide efficient transport of fluid by capillary action.
Accordingly, embodiments of the disclosed wood-based evaporator may
be formed of any type of wood.
[0096] In some embodiments, the selection of wood may be based on a
particular application as well as the microstructure of the
underlying wood. For example, in some applications, the density of
the wood may be greater than that of the fluid, which would
otherwise cause the evaporator to sink in a body of the fluid.
Accordingly, wood for the evaporator may be selected so as to have
a lower density than the fluid, so that it naturally floats in the
body of fluid. In another example, selection of the wood for the
evaporator may be based on the porosity and/or lumen size of the
wood, as discussed elsewhere herein.
[0097] As shown in FIG. 4A, a wood-based evaporator 400 can be
formed of a block of natural wood that has been subject to a
horizontal cut, i.e., where wood is cut in a direction
perpendicular to the tree growth direction 206, such that lumen 302
extend along a direction substantially perpendicular to top surface
406 and/or bottom surface 408. Accordingly, fluid 112 is
transported by the lumen 302 (as well as any smaller diameter lumen
(e.g., fiber tracheids) formed in interstitial region 304) from the
bottom surface 408, which is in contact with a fluid source, to top
surface 406, which receives and absorbs insolation 106. The fluid
112 is transported based on the capillary effect of the hydrophilic
microstructures as well as any nano-cavitation effects resulting
from evaporation 114 of fluid at top surface 406.
[0098] The top surface 406 of the evaporator 400 is coated to form
a solar absorption region 402, or is modified to have a solar
absorption region 402. For example, the solar absorption region 402
can be a carbonized portion of the natural wood. Alternatively or
additionally, solar absorption region 402 can comprise a coating of
at least one of nanoparticles, nanowires, graphene, graphene oxide,
reduced graphene oxide, graphite, single walled carbon nanotubes,
double walled carbon nanotubes, multiwalled carbon nanotubes,
polyaniline, carbon black, amorphous carbon, hard carbon, and soft
carbon.
[0099] Thus, the evaporator 400 includes a region 404 that is
substantially natural wood (i.e., preserves the natural
microstructure of the wood) while a region 402 thereof has been
modified to increase the solar absorption of the wood. Heating of
region 402 due to absorption of solar radiation causes evaporation
of fluid at the top surface 406. The natural wood region 404 has a
relatively low thermal conductivity, and thus isolates the heating
to region 402, thereby improving the vapor generation efficiency of
the evaporator 400.
[0100] FIG. 4B shows an exemplary wood-based evaporator 420
according to the principles of FIG. 4A for water extraction,
distillation, or desalination applications. The wood-based
evaporator 420 has a carbonized layer 422 at top surface 406 and a
natural wood region 404. The top carbonized portion 422 acts as an
efficient 3D light absorber layer. Moreover, the channels 302
within portion 422 can guide the incident light via numerous
reflection in the wood mesostructures (e.g., vessels 302), thereby
improving light absorption. Thus, evaporator 420 can absorb
sunlight more effectively than a natural wood layer, as suggested
by FIG. 5A. Additionally, the low thermal conductivity of the
natural wood layer 404 (e.g., approximately 0.2 Wm.sup.-1K.sup.-1)
drastically reduces the heat dissipation from the top carbonized
surface 422, thereby concentrating the heating at the top surface
406 for more efficient steam generation.
[0101] Meanwhile, the natural wood layer 422 provides rapid and
efficient water transport. In particular, the wood-based evaporator
420 has interconnected channels (fiber tracheids 304 with an
average size dt.apprxeq.5-15 .mu.m, and vessels 302 with an average
size dv.apprxeq.50 .mu.m, as shown in FIGS. 4B-4D) within the top
light-absorbing layer 402 as well as the bottom water-pumping layer
404. Due to the hydrophilic polysaccharides (i.e., cellulose
microfibrils and hemicellulose) embedded within the lignocellulosic
walls, the pristine wood portion 404 is hydrophilic, which promotes
rapid water transport between the bottom surface 408 and the top
surface 406. The presence of vessels and/or fiber tracheids also
induces a capillary effect that draws water into evaporator
420.
[0102] Although the lignin of the cell walls reduces the
permeability of water between adjacent cells, lateral water
transport between adjacent vessels and/or tracheids 304 is possible
via pits 308 (with an average size dp.apprxeq.2 .mu.m), as
illustrated in FIG. 4D. This lateral transport can reduce the risk
of cavitation-induced embolism. Thus, the wood-based evaporator 420
has an internal fluidic transport network comprised of the vessels,
fiber tracheids, and/or pits that allow for three-dimensional
transport of water from a surface 408 in contact with water
(whether a body of water or water embedded within soil or sand) to
a solar absorption surface 406 for evaporation.
[0103] After carbonization, the top surface 406 of the wood may
become more porous, as illustrated in FIG. 4C, which is beneficial
to water transport and light absorption during solar steam
generation. The open microchannels 302 within the carbonized top
layer 422 allow water vapor/steam to escape without interference
from any crystallized salt that may build up during the evaporation
process. In some embodiments, the through-channels 302 can
dramatically reduce salt accumulation during device operation due
to highly efficient mass exchange with the salt water source. There
is also a microstructural match at the interface between the
carbonized wood section 422 and natural wood section 404, which
further facilitates efficient water transport.
[0104] A solar thermal device fabricated according to FIG. 4B was
tested to assess its performance with respect to various metrics
relevant to water extraction and desalination. In summary, the
fabricated device of FIG. 4B demonstrated (1) .apprxeq.99% light
absorption (see FIG. 5A); (2) .gtoreq.80% efficiency under 10 sun
illumination, where 1 Copt=1 kW/m.sup.2 (see FIGS. 5D and 5G); (3)
linear operation up to 10 suns (see FIGS. 5B and 5E); (4) stable
operation without corrosion or solar degradation (under 5 sun
illumination for 100 h); (5) long-term stability in seawater
without salt accumulation, and (6) successful water extraction
directly from the ground (sand or soil). FIGS. 5C and 5F illustrate
the measured enhancement factor for the fabricated solar thermal
device of FIG. 4B in groundwater extraction and desalination
applications, respectively, where the enhancement factor (E.F.) is
the ratio of evaporation rate (E.R.) with the evaporator of FIG. 4B
to the E.R. without the evaporator.
[0105] As noted above, the solar thermal device fabricated
according to FIG. 4B can exhibit continuous and stable operation
over extended use in desalination applications. In particular, the
device was tested with concentrated illumination of 5 suns for over
100 h without issue. Salt deposition was generally only apparent
when illumination intensities were greater than or equal to suns,
which indicates that at higher illumination intensities the surface
evaporated water cannot be readily replenished by the water that
refills the channels. In this case, the amount of salt that
deposits on the wood surface increases to a level that can be
observed. However, salt accumulation may not be an issue for
ambient solar irradiation (1 sun) since the relatively slow
evaporation rates at lower illumination intensities hinder the
ability of salt to reach its crystallization concentration.
[0106] Nevertheless, the salt that accumulates during operation
under 5 suns does not noticeably reduce the steam generation
performance. Furthermore, the solar thermal device fabricated
according to FIG. 4B can exhibit a unique self-regenerating
ability. At night, or other periods of reduced or no insolation,
the natural wood region 404 continues to pump water via its fluidic
transport network even though evaporation via top surface 406 is
reduced or stops. The continuous water transport allows the
precipitated salt within the wood structure to dissolve (for water
soluble salts, such as NaCl and KCl) and/or to fall (for sparingly
soluble salts, such as calcium carbonate, calcium sulfate, and
magnesium hydroxide) back to the surrounding seawater.
[0107] The differences in microstructure of different wood species
result in differences with respect to densities, porosities,
thermal conductivities, and mechanical properties, thereby
providing tunable functionalities that can be utilized in various
applications. For example, various solar thermal devices according
to FIG. 4B were fabricated using different wood materials. FIG. 5H
shows the measured evaporation rates for those solar thermal
devices under different illumination conditions. Wood having a
higher porosity (e.g., poplar) generally resulted in higher
efficiency as compared to lower porosity wood (e.g., cocobolo), due
to higher water absorption and lower thermal conductivity.
Moreover, the lower density of higher porosity wood generally
resulted in a greater increase in temperature as compared to higher
density wood, which may be attributed to the higher incident light
absorption of the carbonized layer and the light capturing
capability of the wood microchannels.
[0108] As shown in FIG. 6A, a wood-based evaporator 600 can be
formed of a block of natural wood that has been subject to a
horizontal cut similar to the wood-based evaporator 400 of FIG. 4A.
However, in contrast to evaporator 400, which has a solar
absorption layer 402 at top surface 406, evaporator 600 has a
plurality of particles 602 deposited on the natural wood structure.
The particles 602 can be disposed over at least the top surface 604
of the wood block. In some embodiments, the particles 602 can be
disposed over cell walls within the wood (e.g., surfaces of vessels
302 and/or tracheids in interstitial region 304), bottom surface
606, and/or external side surfaces of the wood.
[0109] For example, the particles can comprise one or more of
nanoparticles, nanowires, graphene, graphene oxide, reduced
graphene oxide, graphite, single walled carbon nanotubes, double
walled carbon nanotubes, multiwalled carbon nanotubes, polyaniline,
carbon black, amorphous carbon, hard carbon, and soft carbon. In
some embodiments, the particles are plasmonic metallic
nanoparticles formed of Au, Pt, Pd, Ru, Fe, Co, Ni, Sn, or Mo. The
particles 602 act to improve the solar absorbance of the natural
wood.
[0110] For example, FIGS. 6B-6C show an exemplary wood-based
evaporator 620 fabricated according to the principles of FIG. 6A
for water extraction, distillation, or desalination applications.
In particular, wood-based evaporator 620 has plasmonic
nanoparticles 602 formed over internal and external surfaces of the
wood block. Thus, unlike the bilayer structure of evaporator 420 of
FIG. 4B, evaporator 620 has a substantially monolayer
structure.
[0111] Portions of channels 302 proximal to top surface 604, which
have diameters much larger than the wavelength of the solar
radiation, can guide the incident light via numerous reflections
and scattering within the wood mesostructures (e.g., vessels 302),
thereby improving light absorption. Enhanced solar absorption of
the wood is also provided by the plasmonic nanoparticles 602, which
convert the incident light into heat based on the plasmonic effect,
i.e., the dipole resonance coupling with the incident light. As a
result, high light absorption can be achieved within a broadband
wavelength range from 400 to 2500 nm, which can harvest most of the
solar energy. Thus, evaporator 620 can absorb sunlight more
effectively than the natural wood layer, as suggested by FIG. 7A,
and with less sensitivity to light incident angle, as suggested by
FIG. 7B. Additionally, the low thermal conductivity of the natural
wood layer, which is not significantly affected by the plasmonic
nanoparticles, helps localize the heating at the top surface 604
for more efficient steam generation.
[0112] Similar to the evaporator 420 of FIG. 4B, the evaporator 620
of FIG. 6C provides rapid and efficient water transport based on
the underlying hydrophilic microstructure of vessels and/or fiber
tracheids. Moreover, the deposition of the plasmonic nanoparticles
is relatively thin compared to the dimensions of the microchannels,
as shown by FIGS. 6D-6G. Indeed, as shown in FIG. 6G, deposited Pd
nanoparticles are only about 5 nm in diameter, whereas the channel
dimensions are on the order of tens of microns. In addition, the
fluidic transport network of the wood maintains hydrophilic
properties despite the deposition of the nanoparticles. Thus, the
nanoparticles do not obstruct the flow of fluid through the fluidic
transport network of the wood block, i.e., from the bottom surface
606 to the top surface 604.
[0113] In a fabricated embodiment, the wood block of evaporator 620
had a thickness (from the bottom surface 606 to the top surface
604) of approximately 2 cm. When the wood is too thick, the water
uptake to the evaporation layer may be insufficient for solar steam
generation, which decreases the evaporation rate. When the wood is
too thin, the heat generated by absorbed solar radiation cannot be
confined to the top of the evaporator. In other words, heat
dissipates into bulk water 110 and decreases the energy at the
surface 604. Thus, a thickness for the wood block can be selected
with these competing interests in mind. For example, in any of the
disclosed embodiments, the wood block can have a thickness of 5 cm
or less.
[0114] A solar thermal device fabricated according to FIG. 6C was
tested to assess its performance with respect to various metrics
relevant to water extraction and desalination. In summary, the
fabricated device of FIG. 6C demonstrated (1) .apprxeq.99% light
absorption (see FIG. 7A); (2) .gtoreq.85% efficiency under 10 sun
illumination (see FIG. 7E); (3) linear operation up to 10 suns (see
FIG. 7C); and (4) stable operation without corrosion or solar
degradation. FIG. 7D illustrates the measured E.F. for the
fabricated solar thermal device of FIG. 6C, where the E.F. is
defined as the vapor rate of water with the device of FIG. 6C as
compared to bare water.
[0115] Similar to the solar thermal devices of FIG. 4B, the solar
thermal device of FIG. 6C also exhibits a regeneration capability
when operated in a desalination application. In particular, any
salt that accumulates during operation under concentrated
illumination (e.g., .gtoreq.5 suns) can be passively removed during
periods of no or reduced insolation. At night, or other periods of
reduced or no insolation, the evaporator 620 continues to pump
water via its fluidic transport network even though evaporation via
top surface 604 is reduced or stops. The continuous water transport
allows the precipitated salt within the wood structure to dissolve
(for water soluble salts, such as NaCl and KCl) and/or to fall (for
sparingly soluble salts, such as calcium carbonate, calcium
sulfate, and magnesium hydroxide) back to the surrounding seawater.
Thus, solar thermal devices fabricated according to FIG. 6C have
shown excellent cycling performance (e.g., 8 hours of radiation
exposure followed by 16 hours of darkness) in solar steam
generation, without any degradation in performance over 144 hours
of operation.
[0116] As shown in FIG. 8A, a wood-based evaporator 800 can be
formed of a block of natural wood that has been subject to a
horizontal cut similar to the wood-based evaporator 400 of FIG. 4A.
However, in contrast to the evaporator 400 which has a
substantially flat solar absorption layer 402 at top surface 406,
evaporator 800 has a roughened top surface 802. In particular, top
surface 802 can include rough "flower-like" protrusion or
microsheets 808. For example, the protrusions 808 can be formed by
cutting the top surface of natural wood with an electric saw. The
microsheets 808 increase the surface area and elongate the optical
path for multiple scattering, thereby enhancing the light
absorbability.
[0117] The roughened top surface 802 can include solar absorption
coating 806. For example, the coating 806 can comprise one or more
of nanoparticles, nanowires, graphene, graphene oxide, reduced
graphene oxide, graphite, single walled carbon nanotubes, double
walled carbon nanotubes, multiwalled carbon nanotubes, polyaniline,
carbon black, amorphous carbon, hard carbon, and soft carbon.
[0118] In some embodiments, the evaporator 800 may be
chemically-modified to alter physical characteristics thereof. For
example, the natural wood structure can be treated with a chemical
solution to partially remove lignin and hemicellulose, thereby
resulting in a flexible evaporator. The resulting composition of an
exemplary flexible wood evaporator is reflected below in Table 1.
The chemically treated wood can be subject to freeze drying (e.g.,
for 2 days) or critical point drying in order to maintain an
unblocked structure for the cell lumen.
TABLE-US-00001 TABLE 1 Composition of natural wood and resulting
treated wood for use in vapor generation Cellulose Hemicellulose
Lignin Natural Wood (100) 40.0% 15.9% 24.0% Treated Wood (200)
37.6% 11.6% 19.8%
[0119] For example, FIGS. 8B-8C show an exemplary wood-based
evaporator 820 fabricated according to the principles of FIG. 8A
for water extraction, distillation, or desalination applications.
In particular, the wood-based evaporator has a coating 806
comprised of carbon nanotubes (CNTs) on microsheets 808 of top
surface 802, which CNT coating 806 can act to improve the solar
absorbance of the natural wood. FIG. 8D is a magnified view of
region 815 in FIG. 8C, illustrating the coupling between CNT
coating 806 and wood surface 808. In a fabricated example, the mass
percentage of coating 806 of the CNTs was 0.3-0.5 wt %. The
flower-like surface was uniformly coated with layer 806 of CNTs,
while the inside of channels 302 remained smooth without CNT
coating. Strong interactions and connections between CNTs and the
wood matrix result from the abundant --OH and --COOH groups on the
surface of the CNTs and --OH groups on the cellulose, as
illustrated in FIG. 8D.
[0120] Thermal losses can be minimized by localizing the
photothermal generation at the air-water interface within the
thermally insulating wood matrix, in particular by restricting the
coating 808 to an upper region of the device 820. The wood itself
is also a good thermal insulator, such that the majority of the
generated heat will be localized at the top surface 802. As
illustrated in FIG. 8C, when sunlight 106 illuminates evaporator
820, the rough, coated, flower-like surface 808 will absorb the
sunlight 106 and generate localized heating at the fluid-air
interface. As a result, the local temperature increases and
evaporates the fluid. The resulting vapor 114 escapes to the
atmosphere, or can be captured for distillation purposes (e.g.,
converting salt water to freshwater, or converting contaminated
water to potable water). As water proximal to upper surface 802
continuously evaporates, water from the bottom of evaporator 820
will simultaneously be pumped through evaporator 820, via vessels
302 and other natural interconnected channels in the wood. In
particular, the negative pressure at the top of the evaporator
induces capillary forces within the substrate channels that have
smaller diameters than vessels, thereby moving fluid to the top 802
of the evaporator 820.
[0121] As noted above, in some embodiments, the natural wood may be
subjected to partial delignification by treatment with a chemical
solution. Such treatment can break some tracheid cell walls to form
larger microchannels by connecting adjacent cell lumen 302, both
vertically and tangentially, for potential transpiration of water.
There also exist nanopores (i.e., nanochannels) between the aligned
cellulose fibrils of cell walls due to the partial removal of
hemicellulose and lignin, which can improve the water transpiration
capability of the wood matrix through capillarity. Thus, fluid can
be passively pumped to top heated surface 802 from the opposing
bottom surface via capillary action and/or nano-cavitation
effects.
[0122] A solar thermal device fabricated according to FIG. 8C was
tested to assess its performance with respect to various metrics
relevant to water extraction and desalination. In summary, the
fabricated device of FIG. 8C demonstrated (1) .apprxeq.98% light
absorption for wavelengths between 300 nm and 1200 nm; (2)
.gtoreq.80% efficiency under 10 sun illumination (see FIG. 9B); (3)
linear operation up to 10 suns (see FIG. 9A); and (4) stable
operation without corrosion or solar degradation over multiple
cycles (e.g., 20 cycles under 7 sun radiation).
[0123] In further embodiments of a wood-based solar thermal device,
the direction of the lumen within the wood can be perpendicular to
a direction of fluid flow through the evaporator. For example, FIG.
10A shows a wood-based evaporator 1000 formed of a block of natural
wood that has been subject to a vertical cut, i.e., where wood is
cut in a direction parallel to the tree growth direction 206, such
that lumen 302 extend along a direction substantially parallel to
top surface 1006 and/or bottom surface 1008. Accordingly, fluid 112
is transported via smaller pores (e.g., pits and/or spirals)
between the lumen 302 (as well as any smaller diameter lumen (e.g.,
fiber tracheids) formed in interstitial region 304) from the bottom
surface 1008, which is in contact with a fluid source, to top
surface 1006, which receives and absorbs insolation 106. The fluid
112 is transported based on the capillary effect of the hydrophilic
microstructures as well as any nano-cavitation effects resulting
from evaporation 114 of fluid at top surface 1006.
[0124] Similar to the device of FIG. 4A, the top surface 1006 of
evaporator 1000 can be coated to form a solar absorption region
1002, or can be modified to have a solar absorption region 1002.
For example, the solar absorption region 1002 can be a carbonized
portion of the natural wood. Alternatively or additionally, solar
absorption region 1002 can comprise a coating of at least one of
nanoparticles, nanowires, graphene, graphene oxide, reduced
graphene oxide, graphite, single walled carbon nanotubes, double
walled carbon nanotubes, multiwalled carbon nanotubes, polyaniline,
carbon black, amorphous carbon, hard carbon, and soft carbon.
[0125] Thus, the evaporator 1000 includes a region 1004 that is
substantially natural wood (i.e., preserves the natural
microstructure of the wood) while a region 1002 thereof has been
modified to increase the solar absorption of the wood. Heating of
region 1002 due to absorption of solar radiation causes evaporation
of fluid at the top surface 1006. The natural wood region 1004 has
a relatively low thermal conductivity. Moreover, the thermal
conductivity in a cross-plane direction (i.e., perpendicular to the
tree growth direction 206) is less than the thermal conductivity in
an in-plane direction (i.e., along the tree growth direction 206),
as shown in FIG. 11A. Some lumen 302 may at least partially contain
air during operation and thus further improve the thermal
insulation characteristics in the cross-plane direction. For
example, the uppermost lumen 302, proximal to the top surface 1006,
may be disposed above the fluid surface and thus least partially
contain air during operation.
[0126] As a result, the evaporator 1000 of FIG. 10A may enjoy
improved thermal isolation of region 1002 as compared to the
evaporator 400 of FIG. 4A, thereby improving the vapor generation
efficiency of the evaporator 1000. Indeed, the evaporator of FIG.
10A may enjoy higher efficiency and be more readily scalable than
the evaporator of FIG. 4A.
[0127] FIG. 10B shows an exemplary wood-based evaporator 1020
fabricated according to the principles of FIG. 10A for a water
extraction, distillation, or desalination applications. The
wood-based evaporator 1020 has a thin coating (e.g., .about.50
.mu.m) of graphite at top surface 1006 and a natural wood region
1004, as also illustrated in FIG. 10F. The graphite coating acts as
an efficient solar radiation absorbing layer. Thus, evaporator 1020
can absorb sunlight more effectively than the natural wood layer,
as suggested by FIG. 11B.
[0128] Additionally, the low thermal conductivity of the natural
wood layer 1004 in the cross-plane direction (e.g., approximately
0.11 Wm.sup.-1K.sup.-1 versus 0.35 Wm.sup.-1K.sup.-1 in the
in-plane direction) further reduces the heat dissipation from the
top carbonized surface 1002, thereby concentrating the heating at
the top surface 1006 for more efficient steam generation.
Meanwhile, the relatively larger in-plane thermal conductivity
allows the absorbed heat to be more readily conducted along the
lumen 302, for example, to avoid hot spots and increase the amount
of fluid converted to vapor.
[0129] Despite lumen 302 being oriented perpendicular to a
direction of desired fluid flow, the natural wood layer 1004 still
provides rapid and efficient water transport. As illustrated in
FIGS. 10C-10E, smaller pores (e.g., .ltoreq.3 .mu.m in diameter),
such as pits 308 and/or nanoscale spirals 310, fluidically connect
adjacent vessels 308 and/or fiber tracheids in interstitial region
304. The hydrophilic nature of the wood microstructures, coupled
with capillary and any nano-cavitation effects, continue to pull
water into wood block. The pits 308 and spirals 310 can serve as
the backbone of the fluidic transport network in moving fluid
through evaporator 1020 to its top surface 1006.
[0130] A solar thermal device fabricated according to FIG. 10B was
tested to assess its performance with respect to various metrics
relevant to water extraction and desalination. In summary, the
fabricated device of FIG. 10B demonstrated (1) .gtoreq.95% light
absorption for wavelengths between 200 nm and 2500 nm (see FIG.
11B); (2) .gtoreq.89% efficiency under 10 sun illumination (see
FIG. 11E); and (3) linear operation up to 10 suns (see FIG. 11D).
FIG. 11C illustrates the temporal response of evaporation of the
solar thermal device fabricated according to FIG. 10B under 1 sun
illumination conditions, where the solar thermal device results in
a four-fold enhancement over pure water evaporation and a fast
warm-up time (e.g., achieving 1 kg-m.sup.-2 h.sup.-1 within 5
minutes of the start of irradiation).
[0131] FIGS. 12A-12B show another exemplary wood-based evaporator
1200 fabricated according to the principles of FIG. 10A for water
extraction, distillation, or desalination applications. Instead of
a graphite coating as in the evaporator 1020 of FIG. 10B,
wood-based evaporator 1200 has a thin top layer 1202 (e.g.,
.about.2 mm) that has been carbonized (i.e., carbon black). The
carbonized top surface 1202 acts as an efficient solar radiation
absorbing layer. Thus, evaporator 1200 can absorb sunlight more
effectively than the natural wood layer, as suggested by FIG. 12C.
The operation of the evaporator 1200 is otherwise similar to that
of evaporator 1020 of FIG. 10B.
[0132] A solar thermal device fabricated according to FIGS. 12A-12B
was tested to assess its performance with respect to various
metrics relevant to water extraction and desalination. In summary,
the fabricated device of FIGS. 12A-12B demonstrated (1) >95%
light absorption over the full wavelength range of 300 nm and 2500
nm (see FIG. 12C); (2) >96% light absorption in a narrower
wavelength range of 300-1400 nm, where solar radiation is mainly
distributed (see FIG. 12C); (3) .gtoreq.89% efficiency under 10 sun
illumination, where 1 Copt=1 kW/m.sup.2 (see FIG. 12D); and (4)
linear operation up to 10 suns (see FIG. 12D).
[0133] As noted above, when some embodiments of the wood-based
evaporator are used in salt water applications with sufficiently
high solar concentration, salt deposition can occur on the top
surface of the wood-based evaporator. While such salt deposition
does not normally affect device operation at sufficiently low solar
concentrations (e.g., .ltoreq.5 sun), the deposition at higher
solar concentrations may impede device performance. Moreover,
higher evaporation rates can cause a gradient of salt concentration
along the wood lumen, with the concentration being higher at the
top surface than the bottom surface. The salt concentration or
timing constraints of the solar cycle may further inhibit the
self-regeneration ability described above. For example, evaporation
rates that are too fast may suppress the back flow of salt solution
in the wood channel, which will cause the enrichment of salt
deposits at the solar absorption surface of the wood, thereby
decreasing efficiency.
[0134] In some embodiments, the wood can be selected to have lumens
(or modified to have holes) of sufficiently large size that allow
for dilution of fluid. For example, FIGS. 13A-13D illustrate a
wood-based evaporator where the wood has been selected to have
naturally large lumen 1306. For example, the selected species of
wood can be one of balsa, elm, and padauk. Nearly-saturated
solution within fiber tracheids in the interstitial regions 1308
and/or at the top surface 1302 can be diluted by the convection
flow through pores 1310 between the channels in the interstitial
regions 1308 and the larger vessels 1306. As with other disclosed
embodiments, the evaporator 1300 can include a top carbonized
region 1302 that improves solar absorption and a natural wood
region 1304 that transports fluid from a bottom surface 1312 to a
top surface 1308 of the carbonized region 1302.
[0135] A solar thermal device fabricated according to FIG. 13A was
tested to assess its performance with respect to various metrics
relevant to water extraction and desalination. In summary, the
fabricated device of FIG. 13A demonstrated (1) .apprxeq.99% light
absorption (see FIG. 14A); (2) .gtoreq.85% efficiency under 10 sun
illumination (see FIG. 14C); (3) linear operation up to 10 suns
(see FIG. 14B); and (4) efficient operation (e.g., >75%
efficiency) for water with salt concentration as high as 20 wt
%.
[0136] Alternatively, or in addition to the wood selection features
of FIG. 13A, the natural wood can be modified to have holes of
sufficiently large size (e.g., 100 .mu.m to 5 mm in diameter,
inclusive) that allow for further dilution of fluid. For example,
as shown in FIG. 4A, a wood-based evaporator 1500 can be formed of
a block of natural wood that has been subject to a horizontal cut,
such that lumen 1508 extend along a direction substantially
perpendicular to top surface 1516 and/or bottom surface 1518.
Accordingly, fluid 112 is transported by the lumen 1508 (as well as
any smaller diameter lumen (e.g., fiber tracheids) formed in
interstitial region 1510) from the bottom surface 1518, which is in
contact with a fluid source, to top surface 1516, which receives
and absorbs insolation 106. The fluid 112 is transported based on
the capillary effect of the hydrophilic microstructures as well as
any nano-cavitation effects resulting from evaporation 114 of fluid
at top surface 1516.
[0137] As with previously described embodiments, the top surface
1516 of the evaporator 1500 can be coated to form a solar
absorption region 1502, or can be modified to have a solar
absorption region 1502. For example, the solar absorption region
1502 can be a carbonized portion of the natural wood. Alternatively
or additionally, solar absorption region 1502 can comprise a
coating of at least one of nanoparticles, nanowires, graphene,
graphene oxide, reduced graphene oxide, graphite, single walled
carbon nanotubes, double walled carbon nanotubes, multiwalled
carbon nanotubes, polyaniline, carbon black, amorphous carbon, hard
carbon, and soft carbon.
[0138] Thus, the evaporator 1500 includes a region 1504 that is
substantially natural wood (i.e., preserves the natural
microstructure of the wood) while a region 1502 thereof has been
modified to increase the solar absorption of the wood. Heating of
region 1502 due to absorption of solar radiation causes evaporation
of fluid at the top surface 1516. The natural wood region 1504 has
a relatively low thermal conductivity, and thus isolates the
heating to region 1502, thereby improving the vapor generation
efficiency of the evaporator 1500. In addition to vessel lumen
1508, one or more artificial holes 1506 (e.g., formed by drilling,
punching, or any other fabrication technique) can be formed in the
wood so as to extend between top surface 1516 and bottom surface
1518. The artificial hole 1506 can have a larger size (e.g., 100
.mu.m-5 mm in diameter) than that of the vessel lumen (e.g.,
<100 .mu.m in diameter). Fluid 1512 from within lumens 1508
and/or smaller lumen within interstitial region 1510 can be
transported into artificial hole 1506 so as to return to the bulk
fluid. Similarly, any excess fluid at top surface 1516 can also
return to the bulk fluid via artificial hole 1506.
[0139] Artificial holes 1506 can provide a region of relatively
lower salt concentration, as compared to the salt concentrations
within lumen 1508 and lumens within interstitial region 1510. As a
result, a concentration convection flow between the artificial
holes 1506 and the cell lumens can be established, which can dilute
the salt solution in the channels prior to precipitation. This
concentration convection flow may thus help to eliminate
precipitation of salt within the cell lumen and/or on top surface
1516 of evaporator 1500.
[0140] FIGS. 15B-15F shows an exemplary wood-based evaporator 1520
fabricated according to the principles of FIG. 15A for water
extraction, distillation, or desalination applications. As with
other disclosed embodiments, the evaporator 1520 can include a top
carbonized region 1502 that improves solar absorption and a natural
wood region 1504 that transports fluid from bottom surface 1518 to
top surface 1516 of the carbonized region 1502.
[0141] A solar thermal device fabricated according to FIG. 15B was
tested to assess its performance with respect to various metrics
relevant to water extraction and desalination. In summary, the
fabricated device of FIG. 15B demonstrated (1) an efficiency that
did not decrease over time despite continuous operation in water
with a high salt content (see FIG. 16A); and (2) an efficiency that
exhibited only a mild decrease despite increasing salt content (see
FIG. 16B). Indeed, the fabricated solar thermal device was able to
operate at high efficiency (e.g., .gtoreq.70%) in salt
concentrations of 20%.
[0142] Although the embodiments of FIG. 15A-15F have been
illustrated using wood having a horizontal cut, embodiments of the
disclosed subject matter are not limited thereto. Rather, in
further embodiments of a wood-based solar thermal device, the
direction of the lumen within the wood can be perpendicular to a
direction of fluid flow through the evaporator, similar to FIG.
10A, and can include one or more artificial holes, similar to FIG.
15A.
[0143] For example, FIG. 17 shows a wood-based evaporator 1700
formed of a block of natural wood that has been subject to a
vertical cut, i.e., where wood is cut in a direction parallel to
the tree growth direction 206, such that lumen 1508 extend along a
direction substantially parallel to top surface 1710 and/or bottom
surface 1712. Accordingly, fluid 112 is transported via smaller
pores (e.g., pits and/or spirals) between lumen 1508 (as well as
any smaller diameter lumen (e.g., fiber tracheids) formed in
interstitial region 1510) from bottom surface 1712, which is in
contact with a fluid source, to top surface 1710, which receives
and absorbs insolation 106. The fluid 112 is transported based on
the capillary effect of the hydrophilic microstructures as well as
any nano-cavitation effects resulting from evaporation 114 of fluid
at top surface 1710.
[0144] Similar to the devices of FIG. 10A and FIG. 15A, top surface
1710 of evaporator 1700 can be coated to form a solar absorption
region 1702, or can be modified to have a solar absorption region
1702. For example, the solar absorption region 1702 can be a
carbonized portion of the natural wood. Alternatively or
additionally, solar absorption region 1702 can comprise a coating
of at least one of nanoparticles, nanowires, graphene, graphene
oxide, reduced graphene oxide, graphite, single walled carbon
nanotubes, double walled carbon nanotubes, multiwalled carbon
nanotubes, polyaniline, carbon black, amorphous carbon, hard
carbon, and soft carbon.
[0145] Thus, evaporator 1700 includes a region 1704 that is
substantially natural wood (i.e., preserves the natural
microstructure of the wood) while region 1702 thereof has been
modified to increase the solar absorption of the wood. Heating of
region 1702 due to absorption of solar radiation causes evaporation
of fluid at top surface 1710. Moreover, as described above with
respect to FIG. 10A, the orientation of lumen 1508 may contribute
to improved thermal isolation of the top surface 1710, thereby
improving the vapor generation efficiency of the evaporator 1000.
In addition, the natural wood of evaporator 1700 can be modified to
have artificial holes 1706 of sufficiently large size (e.g., 100
.mu.m to 5 mm in diameter, inclusive) that allow for further
dilution of fluid, with operational advantages similar to those
described above with respect to FIG. 15A.
[0146] FIG. 18 illustrates a generalized process 1800 for use of a
wood-based evaporator in a solar thermal application that utilizes
generation of a vapor from fluid, such as, but not limited to fluid
extraction, distillation, and desalination. The process 1800 can
begin at 1802 where a wood-based evaporator is provided. In
embodiments, any of the wood-based evaporators disclosed herein can
be provided at 1802. Alternatively or additionally, 1802 can
include the fabrication process 1900 of FIG. 19, which forms a
wood-based evaporator.
[0147] The process 1800 can proceed to 1804, where the wood-based
evaporator is placed in fluid communication with a fluid source,
for example, by contacting a bottom surface of the wood-based
evaporator with the fluid source. The fluid can be water or any
other type of fluid, and the fluid source can be a body of the
fluid (e.g., lake or ocean) or a ground material containing the
fluid (e.g., soil or sand). In some embodiments, the wood-based
evaporator can be constructed to float on the body of fluid, with
the bottom surface within the body of fluid.
[0148] The process 1800 can proceed to simultaneous steps 1806,
which include solar radiation exposure 1808, natural transport of
fluid through the evaporator 1810, and optional transport of fluid
back to the fluid source 1812. For example, 1808 can include
exposing a top surface of the wood-based evaporator to insolation.
The top surface can include a solar absorption coating or region
that increase absorption of the insolation by the evaporator,
thereby heating any fluid at the top surface of the evaporator. In
some embodiments, the exposing 1808 can include concentrating the
insolation, such that the solar radiation incident on the top
surface of the evaporator is greater than 1 sun.
[0149] For example, 1810 can include transporting fluid from the
bottom surface of the evaporator to the top surface of the
evaporator via an internal fluidic transport network of the
evaporator. In particular, the fluidic transport network is formed
by microstructures of the natural wood of the evaporator. The
fluidic transport network can naturally pump fluid through the
network via capillary action and/or nano-cavitation effects.
[0150] For example, optional 1812 can include recirculating fluid
from the top surface or within the fluidic transport network back
to the bottom surface of the evaporator. In such optional
configurations, the evaporator may include natural lumens having a
diameter greater than or equal to 100 .mu.m, or artificial holes
having a diameter of 100 .mu.m-5 mm. As discussed above, such
recirculation can aid in eliminating, or at least reducing, salt
deposits by providing a concentration convection flow between
regions of high salt concentration (e.g., natural lumen having
diameter <100 .mu.m) and low salt concentration (e.g., natural
lumen having diameters .gtoreq.100 .mu.m or artificial holes). For
example, during transport of the fluid between the top and bottom
surfaces 1810/1812, a salinity can be lower in the artificial holes
and/or natural lumens (>100 .mu.m diameter) than other portions
of the fluidic transport network (<100 .mu.m diameter).
[0151] The process 1800 can proceed to 1814, where vapor emanating
from the top surface of the wood-based evaporator is captured, and
the captured vapor is condensed at 1816. The resulting condensed
fluid may thus be considered distilled or desalinated with respect
to the original fluid. Although shown as separate from simultaneous
steps 1806, it is contemplated that the capturing 1814 and/or
condensation 1816 may be concurrent with simultaneous steps 1806.
Moreover, although illustrated separately, it is also possible for
the capturing 1814 and condensation 1816 to happen simultaneously,
for example, by using a structure that simultaneously captures and
condenses, such as the structure 124 illustrated in FIG. 1B.
[0152] FIG. 19 illustrates a generalized process 1900 for forming a
wood-based evaporator. The process 1900 can optionally begin at
1902, where a piece of natural wood is supplied, for example, by
cutting from an existing tree or block of natural wood. The cut may
be a horizontal cut (i.e., perpendicular to the tree growth
direction), a vertical cut (i.e., parallel to the tree growth
direction), or a cut in between a pure horizontal and pure vertical
cut. For a horizontal cut, the wood has cellulose-based lumen
extending along a tree growth direction that is parallel to at
least one of top and bottom surfaces of the wood. For a vertical
cut, the wood has cellulose-based lumen extending along a tree
growth direction that is orthogonal to at least one of the top and
bottom surfaces. For an intermediate cut (between horizontal and
vertical), the wood has cellulose-based lumen extending a tree
growth direction that is at a non-zero, non-orthogonal angle with
respect to at least one of the top and bottom surfaces.
[0153] The natural wood can be any type of hardwood or softwood,
such as, but not limited to, basswood, oak, poplar, ash, alder,
aspen, balsa wood, beech, birch, cherry, butternut, chestnut,
cocobolo, elm, hickory, maple, oak, padauk, plum, walnut, willow,
yellow poplar, bald cypress, cedar, cypress, douglas fir, fir,
hemlock, larch, pine, redwood, spruce, tamarack, juniper and yew.
Selection of the natural wood may be based on desired porosity,
density, mechanical strength, and/or lumen size for a particular
solar thermal application. For example, in some applications, the
density of the wood may be greater than that of the fluid, which
would otherwise cause the evaporator to sink in a body of the
fluid. Accordingly, wood for the evaporator may be selected so as
to have a lower density than the fluid, so that it naturally floats
in the body of fluid. In another example, selection of the wood for
the evaporator may be based on the porosity and/or lumen size of
the wood to provide a recirculating flow, as discussed above.
[0154] After the cutting 1902, the process 1900 proceeds to 1904,
where it is determined if the wood should be chemically treated to
at least partially remove lignin therefrom. The partial
delignification may be used to increase a porosity of the wood
and/or to increase a flexibility of the wood. If it is determined
at 1904 that delignification is desirable, the process 1900
proceeds to 1906. Otherwise the process 1900 proceeds to 1908.
[0155] At 1906, the cut piece of natural wood is subjected to
treatment with a chemical solution to partially (but not fully)
remove lignin and/or hemicellulose therefrom. The treatment is such
that between 5% and 95% of the lignin in the original natural wood
has been removed, while retaining at least some of the cellulose of
the natural wood. The piece of natural wood may be immersed in the
chemical solution and subject to vacuum, so that the chemical
solution can better infiltrate the structure and channels of the
natural wood.
[0156] The chemical solution can include at least one of NaOH,
Na.sub.2SO.sub.3, (NH.sub.4).sub.2SO.sub.3, p-TsOH,
NH.sub.3.H.sub.2O, NaOH+Na.sub.2S, Na.sub.2CO.sub.3,
NaOH+Na.sub.2SO.sub.3, NaOH+(NH.sub.4).sub.2SO.sub.3,
NH.sub.4OH+(NH.sub.4).sub.2SO.sub.3, NH.sub.4OH+ Na.sub.2SO.sub.3,
NaOH+Na.sub.2CO.sub.3, NaOH+AQ, NaOH/Na.sub.2S+AQ,
NaOH+Na.sub.2SO.sub.3+AQ, Na.sub.2SO.sub.3+AQ,
NaOH+Na.sub.2S+Na.sub.2S.sub.n,
Na.sub.2SO.sub.3+NaOH+CH.sub.3OH+AQ, C.sub.2H.sub.5OH+NaOH,
C.sub.2H.sub.8N.sub.2, C.sub.2H.sub.7NO+NH.sub.3--H.sub.2O,
N.sub.2H.sub.4-H.sub.2O, and NaHCO.sub.3, where n in an integer and
AQ is Anthraquinone. However, the mechanical properties of the
treated wood substrate may depend on the pH of the chemical
solution used for the treatment. In particular, solutions having a
pH value greater than 7 may be used in order to produce a treated
wood substrate with improved flexibility.
[0157] For example, NaOH can be used to selectively degrade lignin
and hemicellulose in the wood materials while having little effect
on the cellulose components. The addition of Na.sub.2SO.sub.3 can
help further remove the lignin component and reduce the reaction
time by increasing sulphite groups (SO.sub.3.sup.2-) in the lignin
side chains via sulphonation, thereby allowing the lignin to more
readily dissolve in alkaline solution. The interaction between the
NaOH/Na.sub.2SO.sub.3 and cellulose, hemicellulose, and lignin
molecules can also swell the cell wall, making it softer for
subsequent manipulations (e.g., bending, folding, or twisting).
Accordingly, in some embodiments, an aqueous solution of 2.5M NaOH
and 0.4M of Na.sub.2SO.sub.3 mixed together can be used for as the
chemical solution for the treatment of 1906, although other
solution compositions selected from the above list or otherwise
that satisfy the pH requirement are also contemplated for 1906.
[0158] After delignification 1906, or if it was determined that no
delignification was necessary at 1904, the process 1900 can proceed
to 1908, where it is determined if the wood should include
artificial holes. The artificial holes may be used to provide
recirculation features in the wood that mitigate the effects of
salts in the fluid by allowing for a concentration convection flow.
However, such artificial holes may be unnecessary if the evaporator
will operate in a salt-free fluid, or if the evaporator will
operate under lower insolation conditions (e.g., <5 suns) where
intermittent periods of darkness allow the evaporator to naturally
renew itself by continued pumping of fluid to remove accumulated
salt deposits, or if the wood already has a sufficient number of
large pores (e.g., .gtoreq.100 .mu.m in diameter). If it is
determined at 1908 that artificial holes are desirable, the process
1900 proceeds to 1910. Otherwise the process 1900 proceeds to
1912.
[0159] At 1910, one or more artificial holes are formed in the
piece of wood. The artificial holes can extend from the top surface
of the wood (e.g., the incident surface for solar radiation) to the
bottom surface of the wood (e.g., the surface in contact with the
fluid source). The artificial holes can have diameters of 100 .mu.m
to 5 mm. The artificial holes can extend straight through the
thickness of the wood (i.e., with a direction of extension
perpendicular to the top or bottom surface of the wood) or can be
slanted (i.e., with a direction of extension at a nonorthogonal
angle with respect to the top or bottom surface of the wood). The
artificial holes can be formed by any known technique, including,
but not limited to, drilling, punching, waterjet cutting, and laser
cutting.
[0160] After forming artificial holes 1910, or if it was determined
that no artificial holes were necessary at 1908, the process 1900
can proceed to 1912, where an optional surface preparation is
performed. The optional surface preparation 1912 can prepare the
top surface of the wood for formation of the solar absorption
region in 1914. For example, the surface preparation 1912 can
include cutting the wood to form a roughened top surface. Such
roughened surface may have "flower-like" microsheets extending
therefrom, for example, as described above with respect to FIGS.
8A-8D. Alternatively, surface preparation 1912 can include
polishing the top surface to form a substantially flat surface in
preparation for deposition of a radiation absorbing material.
[0161] The process 1900 can proceed to 1914, where a solar
absorption layer or region is formed at the top surface of the
wood. In some embodiments, 1914 includes coating to form a separate
solar absorption layer on at least the top surface of the wood. For
example, the coating can include at least one of nanoparticles,
nanowires, graphene, graphene oxide, reduced graphene oxide,
graphite, single walled CNTs, double walled CNTs, multiwalled CNTs,
polyaniline, carbon black, amorphous carbon, hard carbon, and soft
carbon.
[0162] When the coating comprises nanoparticles, the coating can be
formed over most internal and external surfaces of the wood, rather
than being isolated to a region at the top surface of the wood. The
nanoparticles can include plasmonic metallic nanoparticles, such as
Au, Pt, Pd, Ru, Fe, Co, Ni, Sn, or Mo. For example, to deposit Pd
nanoparticles, the wood can be immersed in an aqueous solution of
PdCl.sub.2 (0.01 m) and heated at 80.degree. C. In another example,
to deposit Ag or Au nanoparticles, Sn.sup.2+ can be used to reduce
Ag.sup.+ or Au.sup.3+. The wood can be treated with 0.044 m
SnCl.sub.2 and then transferred to 0.01 m AgNO.sub.3 or
HAuCl.sub.4.3H.sub.2O under ultrasonic bath at room temperature.
After 10 minutes, the Ag or Au nanoparticles can be deposited on
the surface of the wood.
[0163] When the coating comprises graphite, the coating can be
formed by flakes of graphite (e.g., having an average size of
.about.0.5 .mu.m). For example, a spray-on graphite solution may be
used to coat the top surface, where a uniform layer of the graphite
flakes is formed after drying. When the coating comprises CNTs, the
top surface of the wood can be immersed in an aqueous solution of
the CNTs and then allowed to dry in air. Repeated immersions and
dryings can be used to build up a layer of the CNTs on the top
surface.
[0164] In some embodiments, 1914 includes forming a solar
absorption region from a region of the wood proximal the top
surface, for example, by carbonizing the top surface of the wood.
For example, the carbonizing can include pressing the top surface
of the wood into contact with a hot surface (e.g., 500.degree. C.).
The thickness of the carbonized solar absorption region can be
controlled based on the amount of time the top surface remains in
contact with the hot surface. For example, a 30-second contact time
of the wood can result in a 3 mm thick carbonized region of the
wood block.
[0165] After forming the solar absorption layer/region 1914, the
process 1900 can proceed to 1916, where another optional surface
preparation is performed. The optional surface preparation 1916 can
adjust for any effects introduced by the formation of 1914. For
example, the surface preparation 1916 can include polishing the
carbonized solar absorption region (e.g., with 2000 grit sandpaper)
and removing any residual or loose carbon (e.g., via compressed
air).
[0166] The process 1900 can proceed to 1918, where the wood-based
evaporator is assembled with other components into a solar thermal
device. For example, the evaporator may be assembled with an
optical system that directs or focuses solar radiation onto the top
surface of the evaporator, a collector that collects vapor
emanating from the evaporator, or a condenser that condenses vapor
from the evaporator. The assembly may be such that the top surface
of the evaporator will be exposed to radiation while the bottom
surface (which is opposite the top surface) will be in contact with
the fluid source.
[0167] It is noted that the order of 1902-1918 in the process of
1900 is meant to be exemplary only, and that other orders are also
possible according to one or more contemplated embodiments. For
example, the determination 1908 and formation of artificial holes
1910 may occur before determination 1904 and delignification 1906,
or after surface preparation 1912, or after surface preparation
1916.
[0168] Embodiments of the disclosed subject matter also provide for
scalability of the disclosed wood-based evaporators to provide
processing of useful quantities of fluid. For example, by employing
vertical cut configurations, large wood-sheets can be formed for
the evaporator, thereby providing a large continuous area for solar
radiation absorption and fluid processing. FIG. 20A illustrates a
vertical cut fabrication setup 2000. The natural wood 2002 may be
in the form of a log or cylindrical bar, with lumina extending in a
direction perpendicular to the page. The natural wood 2002 can be
cut using a rotary lathe 2004, for example, to separate a thin
continuous layer 2006 of natural wood for subsequent processing.
The natural wood layer 2006 can be conveyed to the next step 2008
in the fabrication process, e.g., forming solar absorption
layer/region 2010, for example, by carbonization the wood surface
by heating for 30 s at 500.degree. C. or by coating the wood
surface, as described above with respect to 1914 of process 1900,
to form the final evaporator 2012.
[0169] FIG. 20B shows an exemplary setup 2020 according to the
principles of FIG. 20A. The natural wood 2002 is cut along the wood
growth direction 206, which is compatible with existing large-scale
wood cutting processes (e.g., where a layer is peeled from the wood
with a desired thickness and then pressed to yield a flat board). A
spray 2028 can then be used to deposit a solar absorption layer
2032 (e.g., of 50 .mu.m thickness) of graphite atop the natural
wood 2034 (e.g., of 1.5 cm thickness) to form the final evaporator
structure 2030.
[0170] Alternatively or additionally, scalability can be achieved
by coupling together multiple separate wood-based evaporators,
whether horizontal or vertical cut, into a single structure. For
example, FIG. 21A illustrates an array 2100 of individual
evaporator cells 2102 that have been coupled together using frame
2104, thereby allowing a larger solar absorption and fluid contact
area. The frame 2104 can be formed of wood, which may be the same
or different than the wood used to form the individual evaporator
cells 2102, or of another insulating material. In some embodiments,
the frame 2104 may only be provided around the border of the array
2100, without frame portions between adjacent evaporator cells
2102, in order to maximize the usable area. In other embodiments,
the frame 2104 may be omitted, such that the evaporator cells 2102
are directly coupled to each other. FIG. 21B shows such an
exemplary setup 2110, where the evaporator unit cells 2114 contact
adjacent cells along their side faces.
[0171] Embodiments of the disclosed subject matter also provide for
the temporary or permanent removal of substances or materials from
the fluid, which materials may be adsorbed into the internal
transport network formed by the natural lumen of the wood. As noted
above, when the evaporator is operated in a fluid containing a
salt, the salt can form on the top surface and within the transport
network of the evaporator. By appropriate design of the evaporator,
e.g., by selecting wood having a particular porosity, appropriate
control of the operation of the evaporator (e.g., insolation
level), and removing the evaporator from the fluid prior to renewal
during night or low-insolation periods, salt may be removed from
the fluid by the evaporator.
[0172] In alternative configurations, the wood for the solar
thermal device can be specifically adapted to adsorption of a
particular substance or material. For example, as shown in FIG.
22A, a wood-based adsorber 2200 can be formed of a block of natural
wood that has been subject to a horizontal cut, i.e., where wood is
cut in a direction perpendicular to the tree growth direction 206,
such that lumen 2202 extend along a direction substantially
perpendicular to top surface 2206 and/or bottom surface 2208. As
with the evaporator embodiments, top surface 2206 receives and
absorbs insolation 106, which heats the adsorber 2200. However,
unlike some of the evaporator embodiments, the entirety of the
adsorber 2200 may be subject to formation of the solar absorption
coating/region. For example, the adsorber 2200 can be subjected to
carbonization, such that all internal (e.g., surfaces of the cell
lumen) and external (e.g., top 2206 and bottom 2208 surfaces) are
carbonized, which may increase a porosity of the wood and/or
convert surfaces from hydrophilic to hydrophobic while
substantially maintaining the aligned channel structure of the
natural wood.
[0173] Thus, heating due to solar radiation absorption is not
isolated to the top surface 2206. Rather, the adsorber is heated
throughout its thickness such that any material in contact with the
bottom surface 2208 is also heated. This heating can increase a
mobility of the material 2212, thereby allowing it to enter
adsorber 2200. In particular, material 2212 can be transported via
the capillary effect into the lumen 2202 (as well as any smaller
diameter lumen (e.g., fiber tracheids) formed in the interstitial
region between lumen 2202) from the bottom surface 2208, which is
in contact with a source of the material (e.g., material disposed
on a substrate or within a fluid).
[0174] FIG. 22B shows an exemplary wood-based adsorber 2220
fabricated according to the principles of FIG. 22A for removing
crude oil from water. FIGS. 23A-23D show operation of a fabricated
device according to FIG. 22B to remove crude oil from water. The
adsorber 2220, including top surface 2206, has been carbonized so
as to increase absorption of solar radiation (e.g., >97%
absorbance in the solar spectrum). As a result, the adsorber 2220
is heated by the radiation and also transmits heat to the crude oil
2302 in body of water 110.
[0175] Compared to light oil (e.g., having a viscosity less than 10
mPas), the cleaning of crude oil 2302 at room temperature can be
difficult and relatively inefficient due to its high viscosity
(i.e., over 1000 mPas). But the heating introduced by adsorber 2220
decreases surface tension, apparent viscosity, and/or dynamic
contact angle of the crude oil 2302, thereby leading to
significantly improved mobility of the crude oil 2302. This
enhanced mobility, coupled with the internal microstructure of the
wood, allows the crude oil to be pulled into adsorber 2220 by
capillary action while leaving behind the fluid 110 due to the
hydrophobic nature of the carbonized wood.
[0176] Thus, adsorber 2220 adsorbs the crude oil 2320 from water
110. Once adsorption of the crude oil 2302 is complete, or when the
capacity of the adsorber 2220 has been reached, the adsorber 2220
can be removed from the water 110. Alternatively or additionally,
the crude oil adsorbed into the wood microstructure can be
continuously or periodically removed, thereby renewing the adsorber
2220 for removal of additional crude oil. For example, FIG. 24
illustrates a system 2400 including a pump 2404, which removes
adsorbed material 2412 from the wood-based adsorber 2220 and stores
it in container 2408. As a result, the system 2400 may be capable
of longer duration or continuous operation.
[0177] Although not illustrated in FIGS. 22A-24, it is also
possible for the wood-based adsorber to be formed of wood having a
vertical cut configuration, similar to that of FIG. 10A but with
all surfaces being carbonized or coated. However, in such
configurations, one or more artificial holes may be provided, such
as in FIG. 17, to aid the ingress of the material into the
wood-based adsorber.
[0178] FIG. 25 illustrates a generalized process 2500 for use of a
wood-based adsorber in a solar thermal application that utilizes
heating to improve mobility of a material to be adsorbed, such as,
but not limited to crude oil. The process 2500 can begin at 2502
where a wood-based adsorber is provided. In embodiments, any of the
wood-based adsorbers disclosed herein (or a disclosed wood-based
evaporator appropriately modified to be an adsorber) can be
provided at 2502. Alternatively or additionally, 2502 can include
the fabrication process 2600 of FIG. 26, which forms a wood-based
adsorber.
[0179] The process 2500 can proceed to 2504, where the wood-based
adsorber is placed into contact with a material to be adsorbed, for
example, by contacting a bottom surface of the wood-based adsorber
with a material floating in a fluid source. The material to be
adsorbed can be crude oil or any other type of material, the fluid
can be water or any other type of fluid, and the fluid source can
be a body of the fluid (e.g., lake or ocean) or a ground material
containing the fluid (e.g., soil or sand). In some embodiments, the
wood-based adsorber can be constructed to float on the body of
fluid, with the bottom surface contacting the material within the
body of fluid.
[0180] The process 2500 can proceed to simultaneous steps 2506,
which include solar radiation exposure 2508, transport of material
into the adsorber 2510, and optional removal of material from the
adsorber 2512. For example, 2508 can include exposing at least a
top surface of the wood-based adsorber to insolation. The adsorber
can include a solar absorption coating or region that increases
absorption of the insolation by the adsorber, thereby heating the
adsorber and any material in contact with the adsorber. In some
embodiments, the exposing 2508 can include concentrating the
insolation, such that the solar radiation incident on the adsorber
is greater than 1 sun.
[0181] For example, 2510 can include transporting material from the
bottom surface of the adsorber into the internal fluidic transport
network of the adsorber. In particular, the fluidic transport
network is formed by microstructures of the wood of the adsorber.
In embodiments, the surfaces of the fluidic transport network have
been coated or modified at a same time as the external surfaces
(i.e., top surface). The coating or modification may cause the
surfaces of the fluidic transport network to be converted from
hydrophilic to hydrophobic, thereby resisting entry of fluid into
the adsorber. At the same time, the heating by the adsorber
increases a mobility of the material, thereby allowing the material
to enter the fluidic transport network of the adsorber via
capillary action.
[0182] For example, optional 2512 can include removing the adsorbed
material from the adsorber. In such optional configurations, a pump
may be provided to periodically or continuously remove the
increased-mobility material from the internal fluidic transport
network of the adsorber, thereby freeing space within the internal
fluidic transport network for adsorption of additional material
from the fluid source.
[0183] The process can proceed to 2514 when a period of no or
reduced insolation occurs, when the adsorber has reached its
adsorption capacity, or when there is no more material for
adsorption. If adsorbed material has not been removed from the
adsorber at 2512, then the removal of the adsorber at 2514 with
adsorbed material therein effects removal of the material from the
fluid source.
[0184] FIG. 26 illustrates a generalized process 2600 for forming a
wood-based adsorber. The process 2600 can optionally begin at 2602,
where a piece of natural wood is supplied, for example, by cutting
from an existing tree or block of natural wood. The cut may be a
horizontal cut (i.e., perpendicular to the tree growth direction),
a vertical cut (i.e., parallel to the tree growth direction), or a
cut between a pure horizontal and pure vertical cut. For a
horizontal cut, the wood has cellulose-based lumen extending along
a tree growth direction that is parallel to at least one of top and
bottom surfaces of the wood. For a vertical cut, the wood has
cellulose-based lumen extending along a tree growth direction that
is orthogonal to at least one of the top and bottom surfaces. For
an intermediate cut (between horizontal and vertical), the wood has
cellulose-based lumen extending a tree growth direction that is at
a non-zero, non-orthogonal angle with respect to at least one of
the top and bottom surfaces.
[0185] The natural wood can be any type of hardwood or softwood,
such as, but not limited to, basswood, oak, poplar, ash, alder,
aspen, balsa wood, beech, birch, cherry, butternut, chestnut,
cocobolo, elm, hickory, maple, oak, padauk, plum, walnut, willow,
yellow poplar, bald cypress, cedar, cypress, douglas fir, fir,
hemlock, larch, pine, redwood, spruce, tamarack, juniper and yew.
Selection of the natural wood may be based on desired porosity,
density, mechanical strength, and/or lumen size for a particular
solar thermal application.
[0186] After the cutting 2602, the process 2600 proceeds to 2604,
where it is determined if the wood should be chemically treated to
at least partially remove lignin therefrom. If it is determined at
2604 that delignification is desirable, the process 2600 proceeds
to 2606. At 2606, the cut piece of natural wood is subjected to
treatment with a chemical solution to partially (but not fully)
remove lignin and hemicellulose therefrom, for example, as
described above with respect to FIG. 19. For example,
delignification at 2606 may be used to increase porosity of the
final adsorber, which may aid infiltration of the material into
internal structures of the adsorber. Otherwise the process 2600
proceeds to 2608.
[0187] After delignification 2606, or if it was determined that no
delignification was necessary at 2604, the process 2600 can proceed
to 2608, where it is determined if the wood should include
artificial holes. If it is determined at 2608 that artificial holes
are desirable, the process 2600 proceeds to 2610. At 2610, one or
more artificial holes are formed in the piece of wood, for example,
as described above with respect to FIG. 19. The artificial holes
may be used to increase a porosity of the wood, thereby aiding
infiltration of the material into internal structures of adsorber.
Otherwise the process 2600 proceeds to 2612.
[0188] After forming artificial holes 2610, or if it was determined
that no artificial holes were necessary at 2608, the process 2600
can proceed to 2612, where an optional surface preparation is
performed. The optional surface preparation 2612 can provide
features that further enhance solar absorption. For example, the
surface preparation 2612 can include cutting the wood to form a
roughened top surface. Such roughened surface may have
"flower-like" microsheets extending therefrom, for example, as
described above with respect to FIGS. 8A-8D. Alternatively, surface
preparation 2612 can include polishing the top surface to form a
substantially flat surface.
[0189] The process 2600 can proceed to 2614, where the piece of
wood is subjected to carbonization. In particular, the
carbonization may be such that all (or at least most) internal
(i.e., cell lumen) and external (i.e., top and bottom surfaces)
surfaces of the wood are carbonized. The carbonized external
surfaces can help improve absorption of the solar radiation, while
the carbonized internal surfaces are converted from hydrophilic to
hydrophobic, thereby resisting the infiltration of water into the
adsorber. For example, the carbonizing can include heating the wood
in hot furnace (e.g., .gtoreq.500.degree. C.). The thickness of the
carbonized regions can be controlled based on the amount of time
the wood remains in the furnace.
[0190] Moreover, in some embodiments, the carbonization may be
effective to at least partially decompose the cell walls, thereby
increasing the porosity of the wood. For example, the porosity of
the wood can increase from .about.57% (with 28.2% being small pores
(i.e., less than 20 .mu.m, .mu.6 .mu.m) and 29.2% being big pores
(i.e., 20-70 nm, .about.43 .mu.m)) before carbonization to
.about.74% (with 38.1% being small pores and 35.7% being big pore)
after carbonization. Optionally, further increases in porosity may
be attained by introducing CO.sub.2 activation during the
carbonization.
[0191] After carbonization 2614, the process 2600 can proceed to
2616, where another optional surface preparation is performed. The
optional surface preparation can adjust for any effects introduced
by the carbonization 2614. For example, the surface preparation
2616 can include polishing at least the top surface of the adsorber
(e.g., with 2000 grit sandpaper) and removing any residual or loose
carbon (e.g., via compressed air).
[0192] The process 2600 can proceed to 2618, where the wood-based
adsorber is assembled with other components into a solar thermal
device. For example, the adsorber may be assembled with an optical
system that directs or focuses solar radiation onto the top surface
of the adsorber, a pump that extracts adsorbed material from the
adsorber, and/or a container that stores the extracted material.
The assembly may be such that the top surface of the adsorber will
be exposed to radiation while the bottom surface (which is opposite
the top surface) will be in contact with the
to-be-adsorbed-material.
[0193] It is noted that the order of 2602-2618 in the process of
2600 is meant to be exemplary only, and that other orders are also
possible according to one or more contemplated embodiments. For
example, the determination 2608 and formation of artificial holes
2610 may occur before determination 2604 and delignification 2606,
or after surface preparation 2612, or after surface preparation
2616.
[0194] Although the discussion above focuses on particular
applications of the modified natural wood (e.g., as an evaporator
for water and as an adsorber for crude oil), embodiments of the
disclosed subject matter are not limited thereto. Rather, the
modified natural wood can be applied to other fluids to be
evaporated or other materials to be adsorbed, according to one or
more contemplated embodiments.
[0195] Moreover, although the discussion above focuses on the use
of solar radiation, embodiments of the disclosed subject matter are
not limited thereto. Rather, radiation having different wavelength
ranges from solar radiation could also be used, with the
appropriate modification of the surface absorption layer/region,
according to one or more contemplated embodiments.
[0196] Embodiments of the enclosed subject matter can include a
natural wood material with at least a top surface having been
modified by at least one of surface carbonization to form carbon
black, and coating with graphite, carbon nanotubes (CNTs), metallic
particles (e.g., plasmonic nanoparticles), nonmetallic particles,
polymer, and/or light absorbing materials (e.g., carbon black,
graphene, metal oxide, etc.). The type of wood can be any type of
hardwood or softwood, and may be selected based on porosity, cost,
density, weight, application or any other characteristic. For
example, in those applications where it is desirable to avoid salt
accumulation, the wood may be balsa elm, padauk, or any other wood
having naturally formed lumina of at least 100 .mu.m in
diameter.
[0197] Moreover, in any of the disclosed embodiments, the wood may
be chemically modified. For example, the wood may be subjected to
partial delignification in order to increase porosity or
flexibility of the wood. Alternatively or additionally, the wood
can be chemically treated to alter its hydrophilicity (e.g.,
increase hydrophilicity or increase hydrophobicity) and/or solar
energy absorptivity.
[0198] As noted above, the wood may be vertical cut (i.e., cut
along the tree growth direction, such that the solar absorption
surface is substantially parallel to a direction of extension of
the lumen), horizontal cut (i.e., cut perpendicular to the tree
growth direction, such that the solar absorption surface is
substantially perpendicular to a direction of extension of the
lumen), or an angled cut (i.e., in between horizontal and vertical
cuts, where the solar absorption surface is at a non-zero,
non-orthogonal angle with respect to a direction of extension of
the lumen).
[0199] Moreover, although particular wood shapes have been
discussed herein, embodiments of the disclosed subject matter are
not limited thereto. Other shapes, such as but not limited to bar,
sheet, thin film, and rod, are also possible according to one or
more contemplated embodiments. In addition, the wood can be formed
of composite layers of individual wood shapes. For example,
embodiments of the disclosed subject matter can be formed of
plywood (i.e., sheet with thin layers of wood plies) or other types
of wood board with a well-defined internal fluidic transport
network.
[0200] Indeed, although the term "block" has been used extensively
herein, "block" is not intended to be limiting to any particular
shape or configuration of wood. Rather, where "block" of wood is
specified, any shape of wood would apply, including, but not
limited to a thin sheet (e.g., having a thickness less than or
equal to 5 mm).
[0201] In this application, unless specifically stated otherwise,
the use of the singular includes the plural, and the separate use
of "or" and "and" includes the other, i.e., "and/or." Furthermore,
use of the terms "including" or "having," as well as other forms
such as "includes," "included," "has," or "had," are intended to
have the same effect as "comprising" and thus should not be
understood as limiting.
[0202] In this application, the terms "horizontal" and "vertical"
have been used to define particular cut directions (i.e.,
perpendicular to the tree growth direction and parallel to the tree
growth direction, respectively) or to describe the relative
locations of different components of the disclosed embodiments.
However, the embodiments are not limited to strictly horizontal and
vertical directions. Where such descriptive terms are used, they
are to include deviations therefrom. For example, "horizontal" can
include directions that have a minor vertical component (e.g., up
to 10%) and "vertical" can include directions that have a minor
horizontal component (e.g., up to 10%).
[0203] Moreover, the terms "horizontal," "vertical," "top,"
"bottom," and "side" have been used herein for convenience to
described relative orientations of components and are not intended
to limit an arrangement of the wood with respect to gravity.
Indeed, it is contemplated that in some embodiments of the
disclosed subject matter, the vertical direction may extend
perpendicular to the direction of gravity and the horizontal
direction may extend parallel to the direction of gravity.
[0204] Any range described herein is intended to include the
endpoints and all values between the endpoints. Whenever
"substantially," "approximately," "essentially," "near," or similar
language is used in combination with a specific value, variations
up to and including 10% of that value are intended, unless
explicitly stated otherwise.
[0205] The foregoing descriptions apply, in some cases, to examples
generated in a laboratory, but these examples can be extended to
production techniques. Thus, where quantities and techniques apply
to the laboratory examples, they should not be understood as
limiting. In particular, where specific chemicals or materials have
been disclosed herein, other chemicals and materials may also be
employed according to one or more contemplated embodiments.
[0206] It is thus apparent that there is provided in accordance
with the present disclosure, wood-based solar thermal devices, and
methods for fabrication and use thereof. Many alternatives,
modifications, and variations are enabled by the present
disclosure. While specific examples have been shown and described
in detail to illustrate the application of the principles of the
present invention, it will be understood that the invention may be
embodied otherwise without departing from such principles. For
example, disclosed features may be combined, rearranged, omitted,
etc. to produce additional embodiments, while certain disclosed
features may sometimes be used to advantage without a corresponding
use of other features. Accordingly, Applicant intends to embrace
all such alternative, modifications, equivalents, and variations
that are within the spirit and scope of the present invention.
* * * * *