U.S. patent application number 12/943912 was filed with the patent office on 2011-05-26 for device for harnessing solar energy with vapor insulating heat transfer core.
Invention is credited to Mark W. Miles.
Application Number | 20110120451 12/943912 |
Document ID | / |
Family ID | 44061164 |
Filed Date | 2011-05-26 |
United States Patent
Application |
20110120451 |
Kind Code |
A1 |
Miles; Mark W. |
May 26, 2011 |
DEVICE FOR HARNESSING SOLAR ENERGY WITH VAPOR INSULATING HEAT
TRANSFER CORE
Abstract
A solar collector is provided, in one embodiment. The solar
collector comprises a heat core to convert incident radiation into
heat; a wicking layer spaced from the heat core to absorb infrared
radiation emitted by the heat core due to the conversion of
incident radiation into heat; an inlet to introduce a heat transfer
fluid into the wicking layer; wherein the absorption of the
infrared radiation is by the heat transfer fluid in the wicking
layer and causes a portion of the heat transfer fluid to enter into
a vapor phase thereof which propagates into the heat core where it
undergoes heating; and an outlet to transport the heated vapor
phase of the heat transfer fluid out of the collector.
Inventors: |
Miles; Mark W.; (Atlanta,
GA) |
Family ID: |
44061164 |
Appl. No.: |
12/943912 |
Filed: |
November 10, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12623337 |
Nov 20, 2009 |
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12943912 |
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12830273 |
Jul 2, 2010 |
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12623337 |
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Current U.S.
Class: |
126/635 ;
126/714 |
Current CPC
Class: |
F28D 15/0266 20130101;
Y02B 10/20 20130101; Y02E 10/44 20130101; F24S 10/95 20180501; F24S
2080/01 20180501; F24S 2080/013 20180501; F28D 15/04 20130101; F24S
70/30 20180501; F24S 70/12 20180501; F24S 70/10 20180501 |
Class at
Publication: |
126/635 ;
126/714 |
International
Class: |
F24J 2/32 20060101
F24J002/32; F24J 2/00 20060101 F24J002/00 |
Claims
1. A method for heating a heat transfer fluid, comprising: exposing
a heat core to incident radiation to cause heating of said heat
core, whereupon the heat core emits infrared radiation; introducing
a heat transfer fluid into a wicking layer spaced from the heat
core to absorb the infrared radiation emitted by the heat core,
whereupon at least some of the heat transfer fluid is converted
into a vapor that enters the heat core; heating the vapor in the
heat core; and extracting the heated vapor to perform work.
2. The method of claim 1, wherein heating the vapor comprises
superheating the vapor.
3. The method of claim 1, further comprising controlling a rate at
which the heat transfer fluid is introduced into the wicking layer
to ensure wetness of all portions of the wicking layer.
4. A solar collector, comprising: a heat core to convert incident
radiation into heat; a wicking layer spaced from the heat core to
absorb infrared radiation emitted by the heat core due to the
conversion of incident radiation into heat; an inlet to introduce a
heat transfer fluid into the wicking layer; wherein the absorption
of the infrared radiation is by the heat transfer fluid in the
wicking layer and causes a portion of the heat transfer fluid to
enter into a vapor phase thereof which propagates into the heat
core where it undergoes heating; and an outlet to transport the
heated vapor phase of the heat transfer fluid out of the
collector.
5. The solar collector of claim 4, wherein heat transfer fluid lost
from the wicking layer through conversion into the vapor phase is
replaced through a capillary action that pumps more heat transfer
fluid into the wicking layer through the inlet.
6. The solar collector of claim 5, which is tuned in terms of
ability of the heat core to convert incident radiation into heat,
wicking capacity of the wicking layer, properties of the heat
transfer fluid, separation distance between the heat core and the
wicking layer, and cross-section of the inlet to ensure that all
portions of the wicking layer remain wet with heat transfer fluid
during operation.
7. The solar collector of claim 4, further comprising a housing for
the heat core, and the wicking layer lines an internal surface of
the housing.
8. The solar collector of claim 7, wherein the housing is
planar.
9. The solar collector of claim 7, wherein the housing is
cylindrical.
10. The solar collector of claim 7, wherein a portion of the
housing that is operatively exposed to incident radiation in the
form of solar flux is transparent to the incident radiation thereby
to define a window.
11. The solar collector of claim 10, wherein said window is treated
with an anti-reflective material.
12. The solar collector of claim 4, wherein the wicking layer
comprises a porous material.
13. The solar collector of claim 12, wherein the porous material
comprises film laced with a network of continuous interconnected
passages to create a wicking action through capillary forces.
14. The solar collector of claim 4, wherein the wicking layer
comprises a surface structured material.
15. The solar collector of claim 14, wherein the surface structured
material comprises surface grooves to facilitate a capillary
pumping action.
16. The solar collector of claim 5, wherein the wicking material
facing the housing is transparent to visible light and has an index
of refraction that is matched to that of the heat transfer
fluid.
11. The solar collector of claim 4, wherein the heat core comprises
a thermally conducting metal or a carbon foam matrix.
18. The solar collector of claim 17, wherein the heat core is
treated to make it light absorbing.
19. The solar collector of claim 4, wherein the heat core comprises
a thermally conductive fill material having interstitial spaces to
promote conductive heat transfer to the vapor phase of the heat
transfer fluid.
20. The solar collector of claim 17, wherein the heat core
comprises an axial passage extending through the fill material.
21. The solar collector of claim 18, wherein the heat core
comprises a pair of metal plates each comprising interstitial
spaces to promote conductive heat transfer to the vapor phase of
the heat transfer fluid, the fill material being located within the
metal plates.
22. The solar collector of claim 4, wherein the heat core comprises
a non-porous hollow cylinder filled with a porous material having
interstitial spaces to promote conductive heat transfer to the
vapor phase of the heat transfer fluid.
23. The solar collector of claim 22, wherein the hollow cylinder is
metallic and is able to withstand pressures at least 20 bar.
24. The solar collector of claim 23, wherein the heat core
comprises an egress end that is hermetically sealed with the
outlet.
25. The solar collector of claim 23, wherein the heat core
comprises an ingress end through which the vapor phase of the heat
transfer fluid enters the heat core, said ingress end being plugged
by a capillary pump.
26. The solar collector of claim 25, wherein the capillary pump
comprises a porous material designed to perform a pumping action on
the heat transfer fluid due to variations in pore size.
27. The solar collector of claim 24, wherein the porous material
comprises at least two layers in contact with each other, each
layer having pores of a different size.
28. An energy system, comprising: an array of solar collectors; a
first heat transfer loop coupled to the array to provide a
recirculation path for heated heat transfer fluid from and to the
array; and a second heat transfer loop comprising at least one heat
exchanger to extract heat from the heated heat transfer fluid in
the first heat transfer loop to perform work; wherein at least one
solar collector, comprises: a heat core to convert incident
radiation into heat; a wicking layer spaced from the heat core to
absorb infrared radiation emitted by the heat core due to the
conversion of incident radiation into heat; an inlet to introduce a
heat transfer fluid `into the wicking layer; wherein the absorption
of the infrared radiation is by the heat transfer fluid in the
wicking layer, and causes a portion of the heat transfer fluid to
enter into a vapor phase thereof which propagates into the heat
core where it undergoes heating; and an outlet to transport the
heated vapor phase of the heat transfer fluid out of the
collector.
29. The energy system of claim 28, wherein the first heat transfer
loop comprises an energy accumulation device to store heat from the
heated heat transfer fluid in the first heat transfer loop.
30. The energy system of claim 28, wherein the energy accumulator
selectively adds heat to the heated heat transfer fluid in the
first heat transfer loop.
31. An energy system, comprising: an array of solar collectors; a
heat transfer loop coupled to the array to provide a recirculation
path for heated heat transfer fluid from and to the array; and at
least one heat exchanger positioned within the heat transfer loop
to extract heat from the heated heat transfer fluid; wherein at
least one solar collector in said array comprises: a heat core to
convert incident radiation into heat; a wicking layer spaced from
the heat core to absorb infrared radiation emitted by the heat core
due to the conversion of incident radiation into heat; an inlet to
introduce a heat transfer fluid into the wicking layer; wherein the
absorption of the infrared radiation is by the heat transfer fluid
in the wicking layer, and causes a portion of the heat transfer
fluid to enter into a vapor phase thereof which propagates into the
heat core where it undergoes heating; and an outlet to transport
the heated vapor phase of the working fluid out of the
collector.
32. The energy system of claim 31, wherein the heat transfer loop
comprises an energy accumulation device to store heat from the
heated working fluid in the first heat transfer loop.
33. The energy system of claim 31, wherein the energy accumulator
selectively adds heat to the heated working fluid in the heat
transfer loop.
Description
[0001] This application is a continuation-in-part of U.S. Ser. No.
12/623,337 and U.S. Ser. No. 12/830,273.
FIELD
[0002] Embodiments of the invention relate to devices and methods
to harness solar radiation as an energy source.
BACKGROUND
[0003] Solar collectors are devices designed to convert solar
radiation into heat that can be used to perform work.
[0004] One new design of a solar collector was described in
co-pending U.S. patent application Ser. No. 12/623,337, and U.S.
Ser. No. 12/830,273 the specifications of which are hereby
incorporated by reference. The improved performance of this
collector derives from the fact that a light absorbing heat
transfer core (HTC) resides within the volume of an infrared
absorbing heat transfer or working fluid, including but not limited
to water or other synthetic fluids similar in composition to the
"Dowtherm" line of heat transfer fluids manufactured Dow Chemical
Corporation. A primary requirement of the fluid is that it be
substantially transparent in the visible region of light, and
highly absorbing in the infrared region. The HTC includes a light
absorption component that converts incident solar flux into heat,
which is transferred to the heat transfer or working fluid as it
passes towards and through the body of the HTC. Heat that radiates
from the HTC in the form of infrared radiation is absorbed by the
working fluid and thus prevented from escaping to the ambient
environment. The lower radiative losses result in overall improved
performance of the collector. A design for a solar thermal energy
conversion system was described in co-pending U.S. patent
application Ser. No. 12/396,336 which is hereby also incorporated
by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 of the drawings shows two plots which illustrate the
infrared absorption properties of water.
[0006] FIG. 2 of the drawings illustrates a prior art embedded
absorber solar collector, and a side view of an embedded absorber
solar collector integrated with a regenerator and a condenser.
[0007] FIG. 3 of the drawings shows a side view of both a planar
and a cylindrical solar collector containing a vapor insulated heat
transfer core with low pressure vapor output in accordance with
embodiments of the invention.
[0008] FIG. 4 of the drawings shows a side view of both a planar
and a cylindrical solar collector containing a vapor insulated heat
transfer core with high pressure vapor output, in accordance with
embodiments of the invention.
[0009] FIG. 5 of the drawings shows a schematic diagram for a
thermal energy conversion system incorporating a solar collector
array with low pressure vapor output.
[0010] FIG. 6 of the drawings shows a schematic diagram for a
thermal energy conversion system incorporating a solar collector
array with high pressure vapor output, in accordance with one
embodiment of the invention.
[0011] FIG. 7 of the drawings shows a schematic diagram for a data
processing facility supplied by cooling and heating resource from a
solar thermal energy conversion system, in accordance with one
embodiment of the invention.
[0012] FIG. 8 of the drawings show a schematic diagram for a solar
thermal application dedicated solely to the generation of a cooling
resource, a heating resource, or a combined cooling and heating
resource, in accordance with one embodiment of the invention.
DETAILED DESCRIPTION
[0013] In the following description, for purposes of explanation,
numerous specific details are set forth in order to provide a
thorough understanding of the invention. It will be apparent,
however, to one skilled in the art that the invention can be
practiced without these specific details.
[0014] Reference in this specification to "one embodiment" or "an
embodiment" means that a particular feature, structure, or
characteristic described in connection with the embodiment is
included in at least one embodiment of the invention. The
appearances of the phrase "in one embodiment" in various places in
the specification are not necessarily all referring to the same
embodiment, nor are separate or alternative embodiments mutually
exclusive of other embodiments. Moreover, various features are
described which may be exhibited by some embodiments and not by
others. Similarly, various requirements are described which may be
requirements for some embodiments but not others.
[0015] Plot 100 of FIG. 1 shows the spectrum of radiation emitted
by the sun that strikes the earth's surface. In general it is
useful to absorb and convert as much of this energy as possible.
Plot 100 illustrates that the bulk of the received energy from the
sun resides between the wavelengths of 200 nm to 2400 nm. Plot 102
illustrates the absorption spectrum of water, which is one
candidate heat transfer fluid. As can be seen, water is extremely
transparent to light in the wavelengths from 200 nm to 1000 nm. As
the wavelength increases, the absorption of incident light
increases dramatically. This property may be used to advantage, and
there is evidence to suggest that other heat transfer fluids
exhibit similar performance.
[0016] Referring now to FIG. 2, solar collector 202 is shown being
illuminated by incident solar flux 200. This light is transmitted
into the interior where it is absorbed by porous heat transfer core
204. The heat transfer core 204, because it has a light absorption
component on its surface, subsequently rises in temperature due to
absorption of the incoming light. Incoming heat transfer fluid 214,
which could be water, for example, flows along the exterior of the
heat transfer core 204 in the direction indicated by the solid
arrows 207 and 210. As it passes through the body heat transfer
core 204, it rises in temperature via conduction of heat from the
heat transfer core 204. The heated fluid 214 then passes out of the
solar collector 202 through the interior of the heat transfer core
204 indicated by dashed arrows 212. The output heated fluid 216,
can be used to provide useful heat to external components which are
in fluid communication with the collector 202.
[0017] FIG. 2 also shows a conceptual view another collector 220.
The collector 220 includes an exterior housing 238 which contains a
heat transfer core 236, and is mechanically and thermally bonded to
regenerator/condenser assembly 228. In operation, cooled vapor 222,
from an exterior energy thermal energy conversion system,
propagates in the direction indicated by dashed arrow 224. As it
passes through this passage it gives up heat to the assembly and is
cooled. After it makes the turn at 226, it continues to propagate
along in the direction indicated by line 230, which represents
condensed fluid. The bottom exterior surface of
regenerator/condenser assembly 228 is exposed to the ambient
environment. This provides a means to condense the incoming vapor
222 by providing a thermally conducting path to the environment.
Thus heat is rejected to the environment enabling the condensation.
Gap 240 provides thermal isolation between the incoming vapor 222,
and the condensed fluid 230. Capillary pump 232 provides a means
for pumping the condensed fluid 230 along path 234, into the body
of the heat transfer core 236, where it is subsequently heated into
a vapor 242, which can then be utilized by an external thermal
energy conversion system.
[0018] FIG. 3 shows a planar solar thermal collector 300,
containing a heat transfer core (HTC) 310 similar in structure to
that which was described in U.S. patent application Ser. No.
12/623,337, and shown in FIG. 2. In one embodiment, the HTC 310 may
comprise a monolithic thermally conducting metal (copper or
aluminum for example) or carbon foam matrix whose outer surface, or
entire surface, has been coated or treated with a thin film or
stack of thin films such that light that is incident on the outer
surface is completely or substantially absorbed. In this embodiment
the material may be substantially porous with a pore size and
density to optimize the transfer of heat via conduction from the
material of the HTC 310 to any vapor which is passing through it,
while optimizing the pressure drop through the HTC 310. The light
absorbing surface treatment may also be in the form of a chemical
etching process which produces a microscopically textured or
roughened surface whose geometry encourages the absorption of
incident light. In another embodiment the core may be in the form
of a bonded pair of plates whose surface has been perforated via
machining or chemical means, to produce a network of through holes,
and whose interior is filled with a highly thermally conductive
foam material, as described above, or with a metal wire or fiber
mesh, or a structured metal fin array which is substantially
porous. Many alternative fill materials and structures may be
utilized. The porosity of the core and its fill material is
determined by the desired heat transfer coefficient, between the
core and vapor propagating inside, and the desired characteristics
including pressure drop and velocity of any vapor transported
through the core. The porosity may vary in the range of 20-80% more
or less. The pore size has a similar impact on these
characteristics and may vary in the range of tens to hundreds of
microns. The interior of the core may be hollow and provide a space
which could be at least several times the size of the pores in the
core. The light absorbing coating on the HTC should serve to
minimize emission in the near and mid infrared regions as well. HTC
310, is illuminated by solar flux 302 emitted by the sun.
Transparent front plate 304 allows for the passage of solar flux
302, so that it may be absorbed by the HTC 310. It comprises a
material which is highly transparent to visible light, such as
glass or other suitably transparent and environmentally robust
material. Transparent front plate 304 is hermetically bonded to
housing 306 such that it can sustain a vacuum and prevents the
passage of gasses in the environment into the housing 306, and the
passage of gasses from the interior of the housing 306 to the
environment. The primary characteristics of the housing 306 are
that it preclude the passage of such gasses and vapors, be
mechanically robust for exposure to an external environment, and be
thermodynamically compatible with the transparent front plate 304.
Transparent front plate 304 may also have resident on one or both
of its surfaces an antireflective coating one type or another, of
which there are many designs known to those skilled in the art of
designing and manufacturing antireflective coatings. Many materials
including metals, and fiberglass or carbon composites suitably
coated with barrier materials, can provide this function. The
transparent front plate 304 and housing 306 have external conduits
318 and 312 which provide a means for the input of condensed heat
transfer/working fluids (HTF) 322, and output of heated vaporized
HTF 320, respectively. Additionally the transparent front plate 304
and housing 306 have a porous or surface structured wicking
material 308, resident on the entire extent of their interior
surface. This material is dimensioned and structured so as to act
like a capillary wick for the HTF which resides within it.
[0019] A porous wicking material means a film whose interior is
laced with a network of continuous interconnected passages to allow
for the pumping, via capillary forces, and propagation of the HTF.
A surface structured wicking material has a surface (an array of
microscopic grooves for example) which has been defined to promote
the capillary pumping and propagation of HTF along the interior
surface. Many variations on porous and surface wicks are possible
and well understood by those skilled in the art of fabricating
capillary wicks, especially for use in heat pipes. Characteristics
of the wick on the interior surface of the front plate include high
transparency to visible light, and a refractive index close to that
of the HTF to be utilized. One candidate is Teflon, but there are a
variety of plastics and oxide materials which may suffice.
Characteristics of the wick on the interior surface of the housing
do not require transparency to visible light. The transparent front
plate 304, housing 306, HTC 310, surface structured wicking
material 308, and conduits 312,318 collectively define a planar
solar collector. Planar means that the lateral dimensions (as
extending left to right on the page, and into the page) are
substantially larger than the vertical (thickness) dimension
(extending top to bottom on the page). Typical dimension are in the
range of several to tens of centimeters for the thickness, and 0.5
to 1 meter for the lateral dimension. As described within the
aforementioned patent applications, some kind of interior support
structure array may be required if the collector is to operate at
interior pressures which are sub-atmospheric. The overall design
goal of such supports is to minimize the transfer of heat via
conduction from the core to the transparent front plate, and
housing 306, while providing mechanical support between these two
components to withstand the pressure of the external
atmosphere.
[0020] The light from the solar flux 302, which is absorbed by the
HTC 310, is subsequently converted into heat, thus the temperature
of the core rises. Subsequently heat radiated from the core in the
form of infrared radiation 314, is incident on the HTF which is
resident within or on the surface of the interior wick. Because the
heat HTF absorbs in the infrared, the temperature of the HTF is
subsequently increased and results in evaporation of the HTF. HTF
input conduit 318, is in fluid communication with the wick. Thus as
the HTF is evaporated it is replaced by additional HTF supplied via
the capillary forces which act on the HTF to pump it through the
wick. The wick is designed to have a pumping capacity which is at
least equal to, though nominally somewhat exceeds, the rate at
which evaporation extracts the fluid under normal operating
conditions. The rate of evaporation is determined by a number of
factors including the initial collector internal pressure, the
characteristics of the core and the wick, the intensity of the
solar flux, as well as the temperature of the condensed HTF
entering the collector among others. As a consequence it may be
necessary to constantly modify the incoming flow rate of HTF 322,
in order to prevent surface structured wicking material 308 from
drying out (at high input energy levels) or flooding (at low input
energy levels), or if other internal or external characteristics of
the collector change over time.
[0021] The HTF vapor 316 emerges from the wick at a temperature
which is slightly above the saturation temperature of the HTF. Due
to the resulting increase in pressure the HTF vapor flows towards
the HTC 310. The vapor undergoes a small amount of superheat due to
the infrared radiation 314 it absorbs, and as it passes through the
body of the core undergoes more substantial superheating due to
further absorption of radiation and conduction to body of the core.
The result is a superheated vapor 320, which is output via conduit
312, and which can be subsequently utilized in a solar thermal
energy conversion system to be described later in the
specification. Typical pressure of the superheated vapor 320 is
less than 1 bar under normal external environmental
temperatures.
[0022] Overall this collector exhibits superior operation and lower
thermal losses because the heat, absorbed by the HTF in the wick,
is transferred to the wick via evaporation. In the aforementioned
applications, and the collector 202 shown in FIG. 2, this heat
transfer is done via fluidic transfer from the wick to the core.
Because HTF vapor has a much lower thermal conductivity, lower
thermal losses can be sustained at lower flow rates. The end result
is the collector is capable of achieving higher outlet temperatures
for a given amount of incident solar flux.
[0023] Referring again to FIG. 3, another solar collector 330 is
shown which is identical in function and operation to the collector
200. In this case, however, a cylindrical geometry is shown which
can be useful for applications wherein concentrating optics is used
to increase the total flux incident on the collector. Transparent
cylinder 334, like the transparent front plate of collector 300, is
made from a material such as glass which could be strengthened by
chemical or thermal treatment, and may have antireflective coatings
on its surfaces. For purposes of this illustration one end of the
cylinder is shown to be hermetically sealed. In certain
applications one or both ends of the cylinder may not be sealed as
the cylinders may be connected in a series fashion to create a
collectively longer cylinder. The interior of cylinder 334 is also
lined with a transparent wicking material 336, which is in fluidic
communication to incoming condensed HTF 332. Suspended in the
center of the cylinder is porous absorber core 338 which comprises
materials which are highly thermally conductive, have internal pore
sizes ranging from tens to hundreds of microns, and are also
treated so that the exposed surface, or perhaps the entire porous
matrix, is highly absorbing to visible light as in collector 300.
Alternative means for achieving porosity, such as the perforation
described in collector 300, may also apply in this configuration.
The core may be hollow to provide supplemental space for vaporized
HTF 342, to be output with relative ease. Similarly the interior
may also contain a heat conducting fill material as described in
collector 300. Similarly the interior may also contain a heat
conducting fill material as described in collector 300. Sunlight
passes through the cylinder and is incident on the core 338 where
it is subsequently turned into heat. The resulting radiation 344
drives evaporation of the HTF resident in the wick, which is
sustainably replaced by the pumping properties of the wick by
incoming fluid 332. This evaporated heat transfer fluid 340, is
forced via pressure differences to propagate into the absorbing
core 338, where it undergoes superheating via some combination of
conductive and radiant heat transfer from the core 338. The
resulting vapor 342, is output to be subsequently used in a thermal
energy conversion system or other system process which can make use
of heat.
[0024] Referring now to FIG. 4, another variation of the planar
collector 400 is shown. In many ways this design is also similar to
the collector shown in FIG. 1. Transparent front plate 404 is
bonded to hermetically sealed housing 410. The interior surfaces of
both are coated with a wick medium 408, which is in fluid
communication with inlet conduits 420. Absorber core or core 412
has a surface which has been treated or coated in a way to maximize
the absorption of visible light and minimize it's emission of
infrared radiation.
[0025] In this case the core 412, is not porous but is a solid
hollow metal cylinder which is capable, due to its material
properties and dimensions, of withstanding high internal pressure.
The bulk of the interior of the absorber core is filled with a
porous material, the superheat matrix 414, nominally a highly
thermally conductive metal, with a pore size and porosity similar
to the cores described in FIG. 3.
[0026] One end of the core is in fluidic communication with and
hermetically sealed too, outlet conduit 424. Thus superheated HTF
vapor 426, may only be output via conduit 424. The absorber core is
plugged on one end by high pressure capillary pump 416. Capillary
pump 416 is a porous material construct of high mechanical
strength. It may be comprised of any one or a combination of
materials including metals, metallic oxides, and carbon which have
been produced in the form of a foam or perhaps, via a sintering
process, into a porous network. There are a variety of other
techniques for producing such materials as known by those who are
skilled in the art, especially the art of manufacturing porous
filtration components. It may comprise materials of different
porosities and pore sizes. High pressure capillary pump 416, is
shown in greater detail in 428. In this example the pump has two
regions of porosity and pore size, regions 430, and 432, though it
may have more. Porous region 430 has a pore size on the order of
tens to hundreds of microns and a porosity nominally exceeding 40%.
Porous region 432 has a pore size of microns or less and a porosity
nominally exceeding 50%. Due to its pore size, region 430 performs
the function of pumping a fluid at relatively low pressure, perhaps
in the range of 0.1 to 5 bar, in addition to providing mechanical
support to region 432. This mechanical support is required because
of the high pressure differential which must be sustained between
the interior of the core and its exterior. Due to its pore size,
region 432 is capable of pumping fluids at higher pressures ranging
from 10 bar to 50 bar or more.
[0027] The transparent front plate 404, housing 410, wick 408, the
core 310 and its components 416 and 414, and the conduits 424 and
420, collectively comprise a high pressure planar collector. Planar
refers to the same dimensional constraints as described in FIG.
3.
[0028] Transparent front plate 404, allows incident light 402, to
be absorbed by the core 412. As the core heats up due to the
incident solar flux, it begins to radiate thus heating the HTF
within the wick 408. Proper design of both the wick 408, and the
high pressure capillary pump 416, as well as proper maintenance of
the internal pressure, among other factors, prevents or inhibits
evaporation of the HTF which flows towards capillary pump 416.
Capillary pump 416, due to its porosity and pore size is capable of
pumping the heated HTF into the superheat matrix 414 against high
pressure. Heat which is conducted from the body of the core to the
capillary plug causes the fluid to vaporize inside the core and
propagate into superheat matrix 414. This drives the pumping of
additional fluid, from wick 408, to replace it. Pressure
differences within the superheat matrix 414, drive the vapor to
propagate towards the other end of the core, and the HTF vapor
absorbs heat via radiative and conductive processes as it does so.
Because of the mechanical properties of the superheat matrix 414,
and the pumping properties of the capillary pump 416, this vapor
may be achieve high pressures exceeding 10 bar without damage to
the collector. The advantage of being able to sustain high output
pressures will be detailed later in this specification.
[0029] Referring again to FIG. 4, a cylindrical solar collector 440
is shown which is identical in function and operation to planar
collector 400 of the same Figure. A transparent cylinder 444 has a
transparent wick 446, resident on its interior surface. Core 450,
is sealed by capillary pump 452 at one end, and the bulk of its
interior occupied by superheat matrix 454.
[0030] Similar in operation to the planar collector 400, sunlight
passes through the cylinder wall of the transparent cylinder 444
where it is incident on core 450, and subsequently converted into
heat. The radiation from the core heats up the HTF 456, which is
propagating in wick 446, and is finally pumped via capillary pump
512, into the interior of the absorber core. There it is turned
into a vapor, then superheated by passage through superheat matrix
454, and output in the form of high pressure superheated vapor 458.
Output temperatures from the collectors described in FIGS. 3 and 4
can theoretically achieve temperatures exceeding 300 C without the
need for mechanisms for tracking the sun or optics for
concentrating the solar flux. With concentration, which can take
the form of parabolic troughs, Fresnel arrays, parabolic dishes,
and other techniques well known and demonstrated commercially,
output temperatures can reach even higher values.
[0031] Referring now to FIG. 5, two heat transfer loops are
illustrated. The first, the heat transfer fluid loop, comprises
vapor and fluid loop sections 504 and 506 respectively, which
collectively form a continuous hermetically sealed conduit loop
through which heat transfer vapor and fluid may flow. The second
loop, the working fluid loop, comprises vapor and fluid loop
sections 518 and 520 respectively which collectively form a
separate hermetically sealed conduit loop. The loops are coupled
via heat exchangers 510, 512, and 514. In general, heat exchangers
510, 512, and 514, provide a means for transferring heat from one
conduit to another without mixing the two fluids between which the
heat is exchanged. The overall goal is to effectively transfer heat
from the heat transfer loop, to the working fluid loop.
[0032] During operation, low pressure solar collector array 502
(which could comprise planar and/or cylindrical collectors as
described earlier), is illuminated by the sun 500 and the resulting
heat in the form of a superheated low pressure vapor is carried
away via vapor conduit 504.
[0033] Some portion of this heat may be stored in thermal energy
storage unit 508 which is connected to conduit 504. Thermal energy
storage unit 506, is a sealed tank capable of supporting high
internal pressures and filled with a quantity of water and/or water
vapor at saturation. Input and extraction of thermal energy may be
accomplished by a number of means including those described by the
aforementioned U.S. patent application Ser. No. 12/396,336. The
heat from conduit 504 passes through superheater heat exchanger 510
which lowers the temperature of the vapor, and provides a means for
transferring heat from the vapor in conduits 504 to the vapor in
conduits 516. The vapor continues to flow to boiler heat exchanger
512, which lowers the temperature of the vapor further,
transferring additional heat to the fluid passing through the heat
exchanger via conduit 518. Finally the vapor passes through preheat
heat exchanger 512, where it is condensed into a liquid. This
liquid passes into fluid conduit 506 where it is pumped via pump
516, back into the collector array 502 where it can be reheated.
This represents a typical solar thermal heat transfer loop though
in this case the pump, 516, may not be necessary or its required
pumping capacity lowered due to the inherent capillary pumping
capacity of the solar collector array.
[0034] The temperature of evaporation in the collector is
determined in part by the total volume of HTF and vapor which
exists in the HTF loop. This combined volume contributes to the
internal operating pressure of the system or the saturation
pressure. The volume and therefore operating pressure of the HTF
loop, can be determined when the system is assembled and/or changed
dynamically during operation to minimize the temperature difference
between the environment and the condensed HTF inside the wick. One
simple means for achieving this dynamic control would be to
incorporate a hermetically sealed reservoir 526, which is coupled
to the system via a pump and valve mechanism. The pump could be
used to decrease the operating pressure of the system by pumping
excess vapor or fluid into the reservoir, and the valve could be
used to release the vapor/fluid from the reservoir into the system.
The pump and valve mechanisms would operate under electronic or
computer control to keep the internal system operating pressure at
a level which relates to the environmental conditions including but
not limited too ambient temperature, solar flux intensity, and wind
conditions. Many means exist for controlling internal pressure
which are well known to those skilled in the art of pressurized
network design. In general, keeping the temperature difference
between the environment and the HTF in the wick further reduces
heat losses to the environment and is the goal of the computer
control system.
[0035] With respect to the working fluid loop, condensed working
fluid is pumped via pump 522 through fluid conduit 520 into heat
exchanger 514 and receives sufficient-heat so that its temperature
is raised to the boiling point. After the heated working fluid
passes through heat exchanger 512, the additional heat boils it and
produces a vapor stream which flows into vapor conduit 518. The
resulting working fluid vapor stream passes through heat exchanger
518 where it is superheated. After this stage the superheated vapor
then passes through utility generation unit (UGU) 524, where it is
converted into various utilities comprising some combination of
electricity, heat and cooling resources for industrial, residential
or other uses. Because the generation of electricity from a heat
source generally requires a working fluid vapor under high
pressure, two separate loops are required in order to maintain low
pressure on the heat transfer loop side, and high pressure on the
working fluid loop side. If the suite of utilities supplied by UGU
524, does not include electricity, then only one loop is required
and heat exchangers 510, 512, and 514, can be eliminated.
[0036] Referring now to FIG. 6, a single working fluid heat
transfer loop is shown comprising vapor loop sections 604, and
fluid loop sections 614. During operation solar flux incident on
high pressure collector array 602, results in a high pressure
superheated vapor stream which flows into vapor conduit 604. In a
fashion similar to that described for FIG. 5, heat may be added to
or extracted from thermal energy storage unit 606 as conditions of
operation merit. The superheated vapor is transported to expander
608 which is in the form of one of many designs for expansion units
(turbines, tesla engines, screw expanders, etc.) which are
manufactured commercially. The function of the expander is to
convert the energy of the expanding vapor into mechanical work
which can be used to drive electric generator 610 to generate
electricity. The expanded vapor emerging from the expander still
has useful heat, thus it flows to UGU 612, which converts and/or
transfers this heat into heating/cooling resources as described
above. The UGU 612, extracts sufficient heat so that the vapor is
condensed and flows into fluid conduit 614. Pump 616 then
transports the fluid back to the collector array where it can be
reheated and converted back into a superheated vapor. As in FIG. 5,
this pump may be optional or require lower pumping capacity based
on the ability of the collector array to pump fluids via capillary
action.
[0037] The expander/generator 608/610 are shown external to the
utility unit (unlike in FIG. 5) to illustrate the point that the
production of high pressure superheated vapor allows the expander
to be directly driven by the output of the collector array. This
cannot be accomplished with the aforementioned low pressure array
as a high pressure difference is required to extract any useful
work from the output superheated vapor. In this regard, a thermal
energy conversion system based on high pressure collectors is
simpler and less costly to construct and maintain.
[0038] It should be noted that while an expander has been described
as a means for converting heat into mechanical energy, to be
subsequently converted electricity, it is not the only option.
Other means for the conversion of heat into electricity include but
are not limited to, thermoelectric devices, fuel cell like thermal
conversion devices, and thermo electron emission devices. Many
versions of these approaches exist and are in various stages of
development by those skilled in the art of such components and
processes. All of these approaches may be incorporated into the
solar thermal conversion systems described above with varying
conversion efficiencies based on the output temperature of the
solar array, the condensing temperature of the environment, and the
particular characteristics of the thermo-conversion technology.
[0039] Referring now to FIG. 7, an integrated application
illustrating how the utilities generated by a solar thermal
conversion system can be exploited is shown. Symbolic block 700,
represents a solar thermally driven UGU comprising many of the
components already described in this specification including, a
solar collector array 704 (driven by the sun 702), thermal storage
unit 706, and UGU 710. These combined represent the solar thermal
conversion system already described. While the connecting heat
transfer loops are not shown, they are implicit in this diagram and
thus the aforementioned components are thermally coupled in a
manner described earlier so that heat input from the solar flux
source is converted and output in the form of electricity and
cooling resource (via a chilled fluid loop) from UGU 710. One
additional component is the hydrocarbon fuel supplemental heat
source 708. This component generates heat by the combustion of a
hydrocarbon fuels such as natural gas, biofuels or fuel oil. This
heat source provides additional or alternative heat to the solar
thermal conversion system should the thermal storage unit 706,
prove inadequate and the solar flux source or solar collector array
be compromised due to inclement weather or some other reason.
Hydrocarbon fuel supplemental heat source 708, is also coupled
thermally to the system so that its heat can be supplied in the
same way the heat from the collector array and the storage unit is
incorporated.
[0040] Symbolic block 712 is a facility which exploits the
electricity and cooling utility output by the UGU 710. In this
example the facility is in the form of a data center comprising, an
array of computational units and/or data storage units and
associated data communications hardware represented by hardware
array 714. Data centers are facilities operated to handle large
data processing tasks driven by the information technology needs of
users 718, which include a variety of businesses and commercial
entities ranging from banking to internet hosting and web
searching. The primary inputs of data centers are in the form of
electricity and a cooling resource, the latter being used to
dissipate the tremendous heat which is generated during the course
of operating the components comprising hardware array 714. Their
primary output is in the form of electronic data exchanged via one
or more of several data exchange means 716, including fiber optic
data links, microwave data links, and more conventional signal
carrying conductive cable arrays, among others. Data centers are
historically located near sources if inexpensive energy
(hydroelectric dams for example) and access points to high
bandwidth communication nodes (fiber optic hubs). In general
proximity to the energy source takes priority as the cost to
construct-high tension lines capable of transmitting the large
amounts of power required are more expensive than installing the
fiber optic cables, or other data exchange mechanism, required to
transmit large amounts of data.
[0041] Given that the highest levels of solar flux are generally
available in remote desert locations, the optimal performance of
solar thermal conversion systems is achieved by locating such
generation facilities far away from where their power could be
utilized. This locational requirement increases the cost of such
facilities since the construction and permitting process for the
related high tension transmission capacity adds cost, complexity,
and delays. Locating an integrated facility, combining the utility
generation capacity of block 700 with the utility consuming and
data processing capability of block 712, at the remote location
where the solar flux is high can reduce costs. The overall cost
reduction comes about due to eliminating the need to establish high
tension transmission capacity, which is very high, at the price of
adding the requisite data exchange means, which is very low. The
lower cost of the data exchange means comes about as a result of
the lower physical footprint and associated infrastructure require
to install some combination of fiber optic, microwave, or other
means for data exchange.
[0042] Referring now to FIG. 8, a solar thermal system dedicated to
producing a heating and/or cooling resource is shown. Solar
collector array 802 is illuminated from the sun 800, to produce a
high temperature working fluid vapor stream into vapor conduit 804.
Thermal storage unit 806, as described in the earlier Figures, can
be used to store excess heat and release it as needed. The working
fluid vapor passes through utility generation unit (UGU) 808 where,
after imparting some portion of its heat, it is condensed and is
pumped by optional fluid pump 810, back to the solar collector
array. UGU 808 is comprised of one of a variety of thermally driven
chiller units which are well understood by those skilled in the art
of manufacturing such components which are both commercially
available and under development. Such chiller include bur are not
limited to absorption chillers, adsorption chillers, and jet vacuum
chilling processes. Another approach involves using an expander, of
the type described earlier, to mechanically drive a compressor unit
as the basis for a conventional vapor compression refrigeration
cycle. A solar thermal conversion system of this sort can benefit
from the small physical footprint of the planar solar collectors
described above, facilitating roof mounted installations and
providing high quality heat without the need for tracking or
concentrating optics.
* * * * *