U.S. patent application number 12/095481 was filed with the patent office on 2010-06-10 for advanced capillary force vaporizers.
This patent application is currently assigned to Vapore, Inc.. Invention is credited to Warren Saul Breslau, Erick Matthew Davidson, Charles Howard Sellers.
Application Number | 20100142934 12/095481 |
Document ID | / |
Family ID | 38092838 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100142934 |
Kind Code |
A1 |
Sellers; Charles Howard ; et
al. |
June 10, 2010 |
Advanced Capillary Force Vaporizers
Abstract
The present invention relates to the vaporization of liquids and
the pressurization of vapors in capillary force vaporizers. More
particularly, the invention provides new developments in the
assembly and configuration of capillary force vaporizers, as well
as systems and methods that incorporate these features, thus
providing capillary force vaporizers that exhibit enhanced
operability and reliability during operation.
Inventors: |
Sellers; Charles Howard;
(Pleasanton, CA) ; Breslau; Warren Saul;
(Berkeley, CA) ; Davidson; Erick Matthew;
(Alameda, CA) |
Correspondence
Address: |
The Firenza Group Ltd.
65 PANORAMA COURT
DANVILLE
CA
94506-6154
US
|
Assignee: |
Vapore, Inc.
Alameda
CA
|
Family ID: |
38092838 |
Appl. No.: |
12/095481 |
Filed: |
November 30, 2006 |
PCT Filed: |
November 30, 2006 |
PCT NO: |
PCT/US06/46030 |
371 Date: |
June 16, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60741646 |
Dec 1, 2005 |
|
|
|
Current U.S.
Class: |
392/387 ;
392/395 |
Current CPC
Class: |
F22B 1/28 20130101 |
Class at
Publication: |
392/387 ;
392/395 |
International
Class: |
F22B 1/28 20060101
F22B001/28 |
Claims
1. An apparatus for the generation of pressurized vapor from an
unpressurized liquid, comprising: a) a porous member further
comprising an insulator and an optional vaporizer, including a
surface for receiving the liquid and an area for the pressurization
of vapor that is produced from the liquid; b) a heater for
conveying heat to the porous member for vaporizing the liquid, the
heater further comprising an area for the collection of vapor and
at least one orifice for release of the vapor at a velocity greater
than zero; c) a retainer for situating the heater in
heat-exchanging contact with the porous member; and d) optionally,
a housing; wherein the porous member draws the liquid towards the
heater via capillary forces.
2. The apparatus of claim 1, wherein the retainer may be selected
from among: tensioning devices, spring clips, clamps and clamping
devices; friction fittings; snap closures; bayonet attachments;
threaded screw closures; twist-lock closures; spring systems
including conical washers, wavy washers, bent leaf springs and coil
springs; welding; chemical, physical or mechanical bonding;
sintering; chemical reaction; gravitational force of the earth; as
well as combinations of any of the foregoing.
3. The apparatus of claim 1, wherein the housing includes a housing
wall present at a spacing of 3 mm, preferably 2 mm and most
preferably 1 mm from the porous member, heater and retainer.
4. The apparatus of claim 1, wherein the insulator selected from
among: ZAL-45AA, Mott Grade 5, AF6, AF15, AF30, AF50, MeAF3,
Micromass, T-Cast, P-10-C, P-16-C, P-40-C and P-55-C; more
preferably selected from among: ZAL-45AA, Mott Grade 5, AF15, AF30,
AF50, MeAF3, Micromass, T-Cast, P-40-C and P-55-C; and most
preferably selected from among: AF30 and MeAF3.
5. The apparatus of claim 1, wherein the retainer is selected from
among: the gravitational force of the earth; tensioning devices
such as spring clips, clamps and clamping devices; friction
fittings; snap closures; bayonet attachments; threaded screw
closures; twist-lock closures; as well as the various types of
spring systems known to those skilled in the art, including conical
washers, wavy washers, bent leaf springs and coil springs; welding;
chemical, physical or mechanical bonding; sintering; glazing;
chemical reaction; as well as combinations of any of the
foregoing.
6. An apparatus for the generation of pressurized vapor in an
environment having pressure at a first pressure above atmospheric
pressure, comprising: a) a porous member further comprising an
insulator including a surface for receiving liquid and an optional
vaporizer including a vaporization area for the collection and
pressurization of vapor that is produced from the liquid, and at
least one opening for release of the vapor at a velocity greater
than zero; and b) a heater component to convey heat to the porous
member for the vaporization of the liquid; wherein the liquid is
present at a pressure of at least that of the first pressure.
7. A technique for the generation of pressurized vapor in
environments having pressure at a first pressure above atmospheric
pressure, comprising the steps of: a) pressurizing a source of
liquid feed to a second pressure; and b) providing the pressurized
liquid feed to a capillary force vaporizer, the capillary force
vaporizer comprising: i) a porous member further comprising an
insulator including a surface for receiving the liquid feed and an
optional vaporizer including a vaporization area for the collection
and pressurization of vapor that is produced from the liquid, and
at least one opening for release of the vapor at a velocity greater
than zero; and ii) a heater component to convey heat to the porous
member for the vaporization of the liquid; wherein the second
pressure is at least equal to the first pressure.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the vaporization of liquids
and the pressurization of vapors in capillary force vaporizers.
More particularly, the invention relates to new developments in the
assembly and configuration of capillary force vaporizers, as well
as systems and methods that incorporate these new features.
[0003] 2. Description of the Pertinent Art
[0004] Many applications utilize gases that have been generated
from liquid sources. Vaporization devices have been designed to
vaporize liquids and release the resulting vapor under pressure. In
applications in which a pressurized vapor stream is desired, prior
art devices generally require that liquid be supplied to the device
under pressure, or that the vapor is otherwise pressurized by
external means. For example, in pressurized boiler systems, liquids
are generally required to be supplied under at least as much
pressure as that of the produced vapor. Pressurized liquid sources
are usually inconvenient to use, heavy to transport, potentially
explosive, and prone to leakage. It is desirable, for many
applications, to produce pressurized vapor streams directly from
liquids that are either at or near atmospheric pressure.
[0005] Several devices that achieve the foregoing goal are known in
the art as capillary pumps, capillary vaporization modules or
capillary force vaporizers. These devices all generate pressurized
vapor directly from unpressurized liquid by applying heat to cause
liquid to boil within a capillary member, and by at least partially
constraining the evolved vapor to allow pressure to increase. Vapor
exits the device through one or more orifices as a high velocity
jet. Other features, which these devices have in common, are that
they all are thermally powered, compact, and generally have no
moving parts, thereby offering certain advantages over other
techniques used for liquid vaporization and vapor pressurization.
Several capillary pumps, capillary vaporization modules, capillary
force vaporizers as well as devices and systems in which they may
be incorporated are variously described in: U.S. Pat. Nos.
6,162,046, 6,347,936 and 6,585,509 to Young, et al.; U.S. Pat. No.
6,634,864 to Young, et al.; U.S. Ser. No. 10/6981,067 to Young, et
al.; U.S. Ser. No. 11/355,461 to Rabin, et al.; and
PCT/US2006/018696 to Rabin, et al.
[0006] While a number of the devices mentioned above offer
advantages over alternative liquid vaporization technologies, many
of the devices are insufficiently robust to enable operation either
for extended periods of time, or over a variety of operating
conditions. For instance, certain of the devices, when operated for
minutes or hours, exhibited fine performance characteristics.
However, during longer periods of operation, namely on the order of
days or weeks, several anomalies in materials performance were
noted. Furthermore, none of these devices are intended or adapted
for use in pressurized environments. That is, none of the devices
described or presented above are configured for use either with
pressurized vapor streams or with pressurized liquid feed sources.
The foregoing devices are primarily intended for use in converting
non-pressurized liquid into vapor, where the vapor that is
generated by the capillary device is ejected at pressures that are
near atmospheric pressure. The ability to generate vapor at
pressures higher than atmospheric pressure is desirable for a
number of reasons. The present invention, therefore, provides
advanced capillary force vaporizers for use in various types of
environments under a variety of operating parameters.
SUMMARY OF THE INVENTION
[0007] The present invention seeks to overcome certain limitations
of, and provide advanced features over prior art capillary force
vaporizers (CFVs) for the vaporization of liquids and the
generation of pressurized vapor. The CFVs described herein are
suitable for use under a variety of operating parameters. These
operating parameters include, but are not necessarily limited to:
reliability over time in cases where a CFV device is used
intermittently; increases in time intervals during which a CFV is
in active operation; variations in power density to the CFV; using
different liquid feed or feed combinations; changes in
environmental operating conditions; and so on. The capillary force
vaporizers of the present invention also feature novel operating
parameters that provide better reliability and improved responses
to changes in input heat and power, in addition to offering other
advantages over prior art devices as will be discussed in greater
detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a graph of bubble point versus flow rate for water
through a variety of monolithic materials evaluated according to
the present invention at a feed pressure of about 0.14
kg-f/cm.sup.2 (2 psi);
[0009] FIG. 2 is a bar graph showing maximum power test results for
various monolithic porous materials evaluated according to the
present invention;
[0010] FIG. 3 is a plot of heater temperature versus time for a
non-preferred CFV operating at 100 Watts;
[0011] FIG. 4 is a schematic cross sectional view of a capillary
force vaporizer according to one embodiment of the present
invention;
[0012] FIG. 5 is a schematic cross sectional view of a capillary
force vaporizer according to a second embodiment of the present
invention; and
[0013] FIG. 6 is a schematic cross sectional view of a capillary
force vaporizer according to a third embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] In early applications that involved the use of capillary
devices, a liquid was fed into or positioned within the device at
or near atmospheric pressure. The liquid feed was generally a fuel
or combustible material, and the purpose for the capillary pump or
capillary vaporization module was the generation of flames for
cooking or for providing light. Accordingly, the devices were
typically operated at temperatures that exhibited flame
temperatures up to about 1090.degree. C. (2000.degree. F.), with
the surface of the device reaching temperatures in excess of about
350.degree. C. (660.degree. F.). However, these prior art devices
were prone to failure modes due to combustion of the very materials
they attempted to vaporize and burn. Often, the devices would
become clogged with the liquid fuel feed being used. Worse yet,
many devices were prone to cracking due to constraints placed upon
device components by the very nature of the peripheral glaze used
in attempts to seal and pressurize the device.
[0015] During the course of the investigations and inventions
described herein, capillary force vaporizers (referred to herein as
CFVs) have surprisingly been shown to be amenable for use in a
larger variety of application areas. Many of these involve
operation at temperatures much lower than capillary devices of the
prior art, namely at temperatures of 250.degree. C., preferably
below 200.degree. C. and often below about 150.degree. C. For
instance, CFV devices have been shown to be useful with non-fuel
feedstocks such as: triethylene glycol; insecticides such as
allethrin and transflutherin; inhalation wellness compounds such as
eucalyptus oil, menthol and camphor oil; water; perfumes,
fragrances, fragrance mixtures and scenting compositions; solvents
such as isopropyl alcohol, toluene and acetone; mixtures for fuel
cell feedstocks such as methanol-water mixtures; and saline
solutions. Other non-fuel feedstocks which may also be used with
CFVs of the present invention include, but are not necessarily
limited to: nicotine formulations, for example, those used for
smoking cessation as well as for tobacco alternative applications;
formulations containing morphine, tetrahydrocannabinol or THC, and
other pain management compounds; formulations containing substances
traditionally inhaled or ingested through smoking; various glycol
ethers formulations such as those used, for example, in eye wetting
and eye lubrication applications; as well as various antihistamine
formulations, for example, those containing loratadine, which may
be useful in treating allergic rhinitis, conjunctivitis and pink
eye; as well as combinations of any of the foregoing. Feedstocks in
addition to those enumerated above may also be used with CFVs of
the present invention. Accordingly, the preceding list is intended
to provide representative examples of CFV feedstocks and should not
be regarded as exhaustive.
[0016] According to one embodiment of the present invention, a CFV
comprises a porous member and a heat source such as a heater. The
porous member further comprises an insulator and an optional
vaporizer. The heater further comprises one or more orifices for
the release of vapor, and a grooved surface in heat-exchanging
contact with the porous member for the collection of vapor and the
concomitant increase in vapor pressure. Optionally, a CFV may also
comprise a mechanical force generator or retainer useful for
maintaining the porous member and heater in heat-exchanging
contact.
[0017] The type of retainer contemplated for use herein may
comprise: tensioning devices such as spring clips, clamps and
clamping devices; friction fittings; snap closures; bayonet
attachments; threaded screw closures; twist-lock closures; as well
as the various types of spring systems known to those skilled in
the art, including conical washers, wavy washers, bent leaf springs
and coil springs; welding; chemical, physical or mechanical
bonding; sintering; chemical reaction; as well as combinations of
any of the foregoing. Note that a threaded screw closure or a twist
lock closure may be comprised of the heater and porous member
components without more, thus obviating the need for additional
parts or hardware, etc. As discussed in greater detail below,
gravity in the form of the earth's gravitational forces may also
comprise one form of retainer acceptable for use with the CFVs of
the present invention. Note further that regardless of the nature
of the method used to provide a mechanical force or retain the
heater in close proximity to the porous member as contemplated in
the present invention, an important distinction between the present
invention and prior art capillary vaporizers is that prior art
devices often featured a sealing member, coating or shroud
peripheral to the device components. By contrast, the retainer of
the present invention contemplates the application of compressive
forces among or between the CFV components.
[0018] In addition to the foregoing, a CFV as contemplated herein
may also optionally comprise a housing. In many applications, a
housing may be useful for situating the CFV within or as part of a
larger instrument, device, engine or apparatus; for ease in
positioning a CFV in close proximity to heater control components;
for convenience in situating a CFV in a particular location within
a room; and so on. Various types of devices that may incorporate a
CFV according to the present invention, particularly with respect
to inline humidification, are described in U.S. Ser. No. 00/000,000
to Weinstein, et al., filed 30 Nov. 2006 for Inline Vaporizer.
[0019] In operation of a CFV, capillary forces transport a liquid
towards a heat source. The heat source vaporizes the liquid, such
that it is emitted from the CFV at or slightly above atmospheric
pressure. Liquid must be delivered to the heat source such that
vaporization can occur in a controlled fashion. At the same time,
heat and excessive vapor must be prevented from migrating from the
heat source to the liquid to prevent failure of the CFV. Early
prior art capillary devices that were used with combustible liquid
feeds for heating, lighting and cooking applications comprised a
wicking member and a heat source. The wicking member delivered the
fuel to the heat source, but these early prior art devices produced
insufficient fuel vapor for the intended application(s). It was
postulated that the wicking member was unable to prevent excessive
heat and pressurized vapor from traveling from the heater towards
the direction of incoming liquid feed, thus resulting in diminished
amounts of vapor being generated for combustion purposes.
[0020] In later prior art capillary devices, the wicking member was
fashioned from material having smaller pores. It was postulated
that the smaller pores would result in higher capillary pressures
realized in the wicking member and thereby prevent excessive vapor
from migrating from the heater towards the liquid feed. However,
the pores of these wicking members were too small, resulting in
unacceptably higher capillary forces. The result was that the
capillary devices that incorporated such wicking members
essentially transmitted fuel at insufficient rates.
[0021] More recent prior art capillary devices incorporated a
combination of the above learnings. That is, a wicking member with
larger pores was used in addition to the wicking member that had
smaller pores. The region with smaller pores is referred to herein
as a vaporizer layer or vaporizer, while the region with larger
pores is referred to herein as an insulation layer or insulator.
Together, the vaporizer and insulator comprise the porous member.
The insulator conducts liquid feed towards the heater or heat
source via capillary forces for vaporization of the liquid without
permitting too much heat from flowing from the heater towards the
advancing liquid feed. As is discussed in greater detail below, the
overall dimensions, capillary pore size and liquid feed are all
factors to be considered in optimizing a given insulator for a
particular application.
[0022] Surprisingly, it has now been found that preventing the
occurrence of too much pressurized vapor from traveling from the
heater towards the direction of the incoming liquid feed may be
achieved in certain CFVs without requiring the use of a separate
vaporizer. In prior capillary devices, the vaporizer had been
considered a necessary layer for preventing too much gas or
pressurized vapor from flowing or migrating from the heater towards
the liquid feed. Vaporizers had been regarded as necessary, for
example, where a CFV was to be operated with very high liquid feed
mass flows, for extended periods of time and/or at very high
operating temperatures as in combustion applications.
[0023] More recently, the desire to operate CFVs at lower
temperatures and pressures and for longer periods of time
necessitated the reevaluation of suitable materials for use as
insulators as well as vaporizers. While the insulator remains an
essential feature of a CFV porous member, vaporizers or
vaporization layers have been found to be optional where CFVs are
operated at lower temperatures and do not involve the generation of
very high internal pressures, as would be experienced with the
combustion of liquid feeds such as fuels, or where very high mass
flow rates and higher temperatures are required. Moreover, it has
been learned during course of the present invention that CFVs for
intermittent use, that is, applications that require bursts of
small amounts of vapor without the buildup of high internal
pressures, may also be developed without the inclusion of a
vaporizer.
[0024] Accordingly, a series of studies were conducted to evaluate
materials suitable for use as vaporizers and insulators.
Surprisingly, it has now been found that through prudent selection
of insulator and vaporizer materials, the relative amount of
vaporizer to insulator required for a particular application can be
significantly modified if not entirely eliminated. Surprisingly
therefore, it was learned herein that in certain instances, as in
the use of CFVs for the vaporization of water and fragrances, it
was possible for a CFV to operate successfully and have liquid feed
converted to vapor without the use of a separate vaporizer in the
porous member. In such instances, and without being bound by
theory, it is theorized that the region of the insulator that is
contacted by the heater serves as the region in which vaporization
of the liquid feed occurs within the capillary pores of the
insulator. Naturally, the absence of a vaporizer layer is not the
most efficient technique for blocking gas generated from the liquid
feed from moving away from the heater and through the insulator
towards the incoming liquid feed. Without a vaporizer layer, the
vapor generated by a CFV exhibits less homogeneity in vapor form
and droplet size. Sputtering and emission of nonvaporized liquid
may also occur. However, for most low mass flow applications,
and/or applications in which CFVs are operated intermittently and
without high boiling point liquids, vaporizers have been shown to
be nonessential. Thus, when CFVs are used with liquid water fed at
a rate of several grams per minute, some loss of water may be
observed if a vaporizer is not used. At lower water flow rates on
the order of a gram per munute or less, numerous trials have shown
that vaporizers are not necessary. According to one embodiment of
the present invention, therefore, a device for the generation of
pressurized vapor from unpressurized liquid comprises: [0025] a) a
porous member further comprising an insulator and an optional
vaporizer, including a surface for receiving the liquid and an area
for the pressurization of vapor that is produced from the liquid;
[0026] b) a heater for conveying heat to the porous member for
vaporizing the liquid, the heater further comprising an area for
the collection of vapor and at least one orifice for release of the
vapor at a velocity greater than zero; [0027] c) a retainer for
situating the heater in heat-exchanging contact with the porous
member; and [0028] d. optionally, a housing;
[0029] wherein the porous member draws the liquid towards the
heater via capillary forces.
A. Selection of Materials
[0030] While numerous materials have adequate permeability to
provide the flow of liquid required by the porous member of a CFV,
a combination of materials properties is appropriate so that the
capillary forces are adequate, excessive pressure does not build up
and thermal and mass transfer requirements are met. In other words,
the liquid feed must be transported to the vaporization region of
the CFV and the flow of liquid within the porous member during
operation of the CFV should result in sufficient cooling without
concomitant pressure buildup so that the CFV maintains a reasonable
temperature and pressure, even at elevated power levels. Capillary
forces due to small pores in a candidate material are essential to
accomplishing these goals. These capillary forces can be quantified
and compared using "bubble point" measurements.
[0031] The bubble point of a material refers to a specific test in
which air is forced through a porous material that has been
saturated with a liquid. The pressure at which a bubble of the
liquid starts to form at a surface of the porous material due to
gas permeation of the saturated material is known as the bubble
point. Common porous materials include simple paper filters, gas
diffusers, construction materials such as bricks, etc. The
foregoing have very large pores and it is very easy to force a
liquid through them. This is because any surface tension due to
wetting of the pores by a liquid passing through the pores is
relatively easily overcome. In these instances, the pressure
required to initiate gas flow through the porous material can be
very low.
[0032] The smaller the diameter of the pores of a material, the
higher the pressure needed to displace a liquid passing
therethrough. Technical porous materials, that is, those designed
for applications in which pore size distribution is critical, are
often described by their maximum through pore size, which in turn
is easily calculated from the bubble point. For vaporization
applications, the bubble point should be high enough to prevent
expulsion of liquid from the pores, but low enough to enable
sufficient quantities of liquid feed to flow through the material.
An acceptable value depends on the nature of the fluid and the
specific application. Materials with very low bubble points can
accommodate very large flow rates, while materials with very high
bubble points can only accommodate very low flow rates. For most
CFV applications, very low flow rates and thus materials with very
high bubble points are not desirable.
[0033] A variety of technical porous materials were evaluated for
use herein. The materials which were studied include those
described in Table 1 below.
TABLE-US-00001 TABLE 1 Materials Evaluated for Use in CFVs Sample
No. Name Description Source 1 ZAL-45AA High porosity alumina
consisting of grains and fibers, Zircar Ceramics, Inc. with a mean
pore size of approximately 5 microns, Florida, NY used primarily
for thermal insulation in high temperature furnaces 2 Mott Grade 5
Porous sintered metal with a mean pore size of Mott Corp.
approximately 5 microns, used for gas and liquid Farmington, CT
filtration 3 AF6 Moderately porous alumina with a mean pore size of
Refractron approximately 5 microns, used for liquid filtration
Technologies Corp. Newark, NY 4 AF15 Moderately porous alumina with
a mean pore size of Refractron approximately 14 microns, used for
liquid filtration Technologies Corp. Newark, NY 5 AF30 Moderately
porous alumina with a mean pore size of Refractron approximately 30
microns, used for liquid filtration Technologies Corp. Newark, NY 6
AF50 Moderately porous alumina with a mean pore size of Refractron
approximately 50 microns, used for liquid filtration Technologies
Corp. Newark, NY 7 MeAF1 Composite porous alumina with 2 distinct
layers, each Refractron having a different mean pore size
(approximately 1 and Technologies Corp. 14 microns), used for water
filtration Newark, NY 8 MeAF3 Composite porous alumina with 2
distinct layers, each Refractron having a different mean pore size
(approximately 3 and Technologies Corp. 14 microns), used for water
filtration Newark, NY 9 Micromass High porosity alumina with a mean
pore size of Selee Corporation, approximately 5 microns, used in
high temperature Hendersonville, NC furnaces as kiln furniture 10
T-Cast High porosity alumina microns, used primarily for Refractory
thermal insulation in high temperature furnaces Specialties, Inc.,
Sebring, OH 11 P-6-C Moderately porous alumina with a mean pore
size of CoorsTek, Golden, approximately 6 microns, used for liquid
filtration CO 12 P-10-C Moderately porous alumina with a mean pore
size of CoorsTek, Golden, approximately 10 microns, used for liquid
filtration CO 13 P-16-C Moderately porous alumina with a mean pore
size of CoorsTek, Golden, approximately 16 microns, used for liquid
filtration CO 14 P-40-C Moderately porous alumina with a mean pore
size of CoorsTek, Golden, approximately 40 microns, used for liquid
filtration CO 15 P-55-C Moderately porous alumina with a mean pore
size of CoorsTek, Golden, approximately 55 microns, used for liquid
filtration CO
[0034] The results of bubble point studies for several of the
foregoing materials are shown in FIG. 1. The sample numbers and
corresponding data for the materials evaluated in FIG. 1 are
provided in Table 2 below. The evaluations were carried out at a
pressure of about 0.14 kg-f/cm.sup.2 (2 psi) with water as the
liquid feed. The materials were evaluated in the form of monolithic
disks shaped 2 cm in diameter with a height of 1 cm.
TABLE-US-00002 TABLE 2 Water Flow Rates and Bubble Points for
Various Material Samples Sample Bubble Point Flow Rate No. (in
kg-f/cm.sup.2) (in cm.sup.3/sec) 4 .021 1.4 6 .021 3.4 5 .028 3 15
.056 2.13 14 .070 0.97 9 .098 1.56 10 .106 1.2 1 .127 1.7 12 .176
0.06 3 .232 0.23 13 .352 0.06
[0035] It has now been surprisingly found that bubble points on the
order of about several tenths kg-f/cm.sup.2 (several psi) are
suitable for use with certain CFV applications, such as with
aqueous systems. Thus, for certain applications, a relatively small
area of FIG. 1 can describe optimal operating properties for CFVs.
For samples having areas of about 3 cm.sup.2, which were used for
the vaporization of water, the region of interest in FIG. 1 lies
between flow rates of 0.01 to 10 cm.sup.3/sec, more preferably
between 0.1 and 5 cm.sup.3/sec, and most preferably between 0.5 and
3 cm.sup.3/sec having bubble points of 0.001 to 10 kg-f/cm.sup.2,
more preferably 0.01 to 0.5 kg-f/cm.sup.2, and most preferably
between 0.025 to 0.2 kg-f/cm.sup.2.
[0036] For other fluids and operating conditions, higher bubble
points may be appropriate. Where a CFV is used to provide vapor
into a pressurized gas environment, for example, a sufficient
bubble point is required such that the feed liquid does not leak or
is not otherwise expelled from the CFV before it can be vaporized.
In such instances, higher bubble points with concomitant higher
liquid flow rates are generally more desirable. An expulsion of
liquid without vaporization would prevent a stable flow of liquid
feed from reaching the vaporization area adjacent to the heat
source. Vaporizing liquids in elevated pressure environments can
also require a pressurized liquid flow to the CFV, as will be
discussed in greater detail below.
[0037] Depending on the requirements of the specific CFV
vaporization application, different combinations of these two
parameters, that is bubble point and flow rate, may be desirable.
For example, certain humidification applications require a bubble
point on the order of about 0.01 to 0.15 kg-f/cm.sup.2 and a flow
rate or permeability of 1 cm.sup.3/sec when a pressure of 1400
kg/m.sup.2 is applied to a disk 2 cm in diameter and 1 cm
thick.
[0038] As the bubble point of a material is determined by its pore
structure, it does not depend upon the thickness of the material,
but rather on the maximum through pore size. The permeability
generally diminishes as the thickness of the material is increased.
In order to provide sufficient flow for a desired power level and
therefore vapor output rate, the thickness of a material can be
manipulated. This is one reason why different vaporizer thicknesses
may be used where it is desirable to prevent the buildup of too
much backpressure within a porous member. See the discussions above
describing the use of CFVs with fuels and combustible liquids.
[0039] In the case of an insulator, by contrast, regardless of the
material chosen, the insulator cannot be too thin or the
temperature of the CFV will be excessive. An appropriate length for
an insulator is that which, when fluid passes through it during
vaporization, it can provide sufficient cooling to allow the CFV to
remain at a temperature well below the boiling point of the fluid.
In this manner, vapor should be produced only near the heat source
and the vapor generated by the CFV is ejected mostly through the
orifice. The optimal thickness chosen for a particular insulator
will necessarily depend upon such parameters as the nature of the
fluid to be vaporized, the duration of operation for the CFV, the
liquid flow rate and necessary power level required, and the
thermal conductivity of the material.
[0040] If the bubble point and the permeability for a particular
CFV vaporization application cannot be met by a porous member
comprising a monolithic material, a CFV can be fashioned with more
than one material comprising the porous member, as in the
combination of an insulator and optional vaporizer, discussed above
for fuel and combustible liquids. It should be noted that the
proper combination of materials for insulator and vaporizer can be
achieved in various ways using one or more components which vary in
pore size distribution and other properties.
[0041] Somewhat surprisingly, it has now been found that
combinations of materials for porous members comprising insulators
and optionally, vaporizers, may be satisfied according to the
following preferred configuration. Materials with finer pores, and
therefore higher bubble points, are situated adjacent to the heat
source while materials having larger pores, and thus higher
permeability, are situated remotely from the heat source. The finer
pore region can supply the necessary capillary force and provide
sufficient permeability even when relatively thin in comparison to
the insulator thickness at a given diameter. The larger pore region
tends to be thicker, so as to provide adequate thermal insulation.
Naturally, CFVs containing layers with more than two different pore
sizes can also be contemplated. Porous members may therefore
comprise materials with constant pore sizes as well as materials
with varying pore sizes, such as graded materials, in which pore
sizes vary when transversing from a first surface to a second
surface across the material.
[0042] Composite structures that contain combinations of fine poor
and large poor regions can arise, for example, from a single
material containing a distribution of pore sizes that may be
introduced during the manufacturing process. The result is a
"graded" material, as there is a gradient in the pore size
distribution in moving through the material. Graded materials may
also be created in a multi-step process in which fine pore material
is integrally bonded to the larger pore material. Alternately, the
same result may be achieved by using two distinct components that
are in intimate contact with each other.
[0043] Permeability and bubble point alone are not sufficient
parameters for predicting suitability for components in all CFVs,
but they can be used to evaluate materials as new materials are
developed. Other parameters that may be important factors can
include evaluation of energy densities that a material can
accommodate for high performance CFV applications, for instance.
Several monolithic materials that were evaluated for maximum
sustainable power levels are shown in FIG. 2. The materials were
evaluated in the form of 20 mm diameter discs with a height of 10
mm. Note that replicates of trials are included in FIG. 2 for
samples numbered four and eight.
[0044] The study summarized in FIG. 2 was carried out in order to
evaluate CFV materials for use in applications that encompass
aqueous feed applications with power level requirements on the
order of about 100 Watts. Sample numbers are those provided above
in Table 1. The fact that a number of samples exhibited good
reliability up to about 120 Watts indicates that these are more
robust materials. Note that materials that exhibited stability at
higher power levels are generally more preferred.
[0045] Other variables that are used to evaluate suitable of a
given material for use in a CFV include such factors as: response
time; reliability of the material over time; potential to
contribute contaminants to the vapor stream; ease and convenience
of manufacturability and associated costs for doing so; etc. Table
3 below illustrates one set of results obtained for a variety of
porous materials evaluated for possible use as the porous member in
CFVs. The following operating characteristics were evaluated: 1)
maximum power, that is, the maximum sustainable operating power,
with higher values preferred; 2) heater temperature, in other
words, the temperature of the heater with a CFV operating at
maximum power, with lower temperatures being preferred; 3) CFV
temperature, that is, the temperature of the CFV device when the
CFV is at maximum power, with lower temperatures preferred; and 4)
friability, in other words, the propensity of the porous material
to generate particulate matter or give up other byproducts during
operation of the CFV, which may also be termed "contaminants."
TABLE-US-00003 TABLE 3 Evaluation of Porous Materials According to
Operating Characteristics Maximum Heater CFV Sample No. Power
Temperature Temperature Contaminants 1 ++ + + - 2 - - - ++ 3 - - -
++ 4 - .smallcircle. - ++ 5 ++ + + ++ 6 - .smallcircle.
.smallcircle. ++ 8 ++ + + ++ Legend to Table 3: "-" indicates poor
performance; ".smallcircle." indicates adequate performance; "+"
indicates good performance; and "++" indicates very good
performance
[0046] The materials that were evaluated for inclusion in Table 3
are: ZAL-45AA; Mott Grade 5; AF6; AF15; AF30; AF50; and MeAF3;
additional information for which can be found in Table 1 above. The
results provided above in Table 3 indicate that not all porous
materials are equally suitable for the development of high
performance CFVs. Those samples that demonstrated the most
favorable characteristics in Table 3 above include samples 5 and 8,
which correspond to AF30 and MeAF3, respectively. According to one
embodiment of the present invention, therefore, a capillary device
for the generation of pressurized vapor from unpressurized liquid
comprises an insulator characterized by material selected from
among: ZAL-45AA, Mott Grade 5, AF6, AF15, AF30, AF50, MeAF3,
Micromass, T-Cast, P-10-C, P-16-C, P-40-C and P-55-C; more
preferably selected from among: ZAL-45AA, Mott Grade 5, AF15, AF30,
AF50, MeAF3, Micromass, T-Cast, P-40-C and P-55-C; and most
preferably selected from among: AF30 and MeAF3.
B. CFV Configuration
[0047] During operation of CFVs having certain configurations, it
has been surprisingly found that there can be a tendency for gas
bubbles to evolve from the sides and bottom of the CFV. Without
being bound by theory, it is speculated that these bubbles
originate in a variety of ways: by accumulation of dissolved gases
present within the feed liquid; as a result of unsaturated porosity
in the porous member, namely in the insulator; etc. The bubbles can
compromise operation of a CFV, since the accumulation of bubbles
can obstruct the flow of liquid feed to the insulator, particularly
when the liquid feed is water as in instances where the CFV may be
used for humidification purposes.
[0048] Depending on the liquid feed, the power level at which the
CFV is operated and the details of CFV construction, failure in
this mode can occur in minutes or hours. In the past, the evolution
of gas bubbles was observed to occur during use of many vaporizers
that were operated on the order of hours minutes or even seconds.
By contrast, it has now surprisingly been found that when properly
vented, CFVs can operate stably and reliably for times on the order
of days to several weeks, even at high power settings.
[0049] In many vaporizers of the prior art, there was no
opportunity for the venting of gas bubbles, as in cases where the
insulator was tightly contained within a sheath, tube, or similar
containment device, or in situations where a deliberate attempt was
made to seal the perimeter of the insulator, as with a coating or
other integral housing. The accumulation of gas inside the porous
structure of the insulator in these vaporizers can and often did
cause serious problems with operation of the device due to
interference by the gas with the flow of liquid to the heater. As
alluded to above, this can cause overheating of the device and
result in heater failure, thus rendering the CFV inoperable.
However, not all prior art vaporizers were prone to failure. Due in
part to microscopic roughness, device housings which only loosely
enclosed the vaporizer may have fortuitously provided a region
which was either empty or contained the fluid to be vaporized, and
thus provided a de facto escape route for gas bubble buildup.
[0050] FIG. 3 shows what can happen in instances where a CFV is
inadequately vented. The graph shown in FIG. 3 is a plot of heater
temperature versus time for a CFV operating at 100 Watts. The
increase in CFV heater temperature was accompanied by the formation
of bubbles over time. Note that the heater temperature climbed
while a constant power level was maintained, until the bubbles had
a chance to escape. The temperature then immediately dropped and
new bubbles started to accumulate. This thermal cycling process is
detrimental to good control of the vaporization process, and can
produce unnecessary strain on the power supply and control circuit.
It can cause undesirable stress on CFV components, as well as place
the CFV at risk for overheating and ultimately, failure.
[0051] Various modifications can be contemplated for the CFV either
to prevent bubbles from accumulating or to provide with an easy
escape route in the event of bubble formation. Those familiar with
the problem of gas generation and bubble formation will understand
that too close a fit between the CFV porous member and a device
housing can constrain bubbles. Accordingly, it is advisable to
design the local environment of the CFV properly. A region can be
provided between the porous member and the housing that is either
continuous or discontinuous, such that evolving bubbles can be
directed or channeled out of the CFV as quickly as possible. This
may be accomplished, for example, by creating channels or gaps in
continuous or selected portions of the device containment
perimeter. The gap can be either fluid filled or contain a gas. A
wide variety of configurations can be used to remedy the situation
of bubble formation. Additionally, there may be features on the CFV
housing, adjacent to the lower portion of the porous member or
insulator thereof, which direct bubbles forming here to the device
perimeter, so that they can escape. Another alternative approach is
to reduce the height of the CFV container or housing, so that it
does not entirely cover the peripheral area of the CFV, so that gas
bubbles are easily dispersed into the ambient environment, away
from the CFV.
[0052] An example of a non-vented CFV is shown schematically in
FIG. 4 at 400, while FIG. 5 shows a schematic of a vented CFV at
500 according to one embodiment of the present invention. An
alternate example of a CFV according to another embodiment of the
present invention is shown schematically in FIG. 6 at 600. Note
that like reference numbers are used throughout the figures to
represent similar parts or features of the drawings.
[0053] Turning first to FIG. 4, the device at 400 illustrates one
example of a capillary force vaporizer according to the present
invention. A porous member for the delivery of liquid feed via
capillary forces comprises insulator 404 and optional vaporizer
402. The porous member is in intimate contact with a heater, which
further comprises heating element 406 and heat exchanger 408.
Heating element 406 is in intimate contact with heat exchanger 408,
which includes orifice 410 for the emission of pressurized vapor
from vapor that collects and becomes pressurized at vapor
collection channels 412, situated at the interface between the
porous member and the heater (not labeled). Electrical leads 414
connect heating element 406 to a power supply (not shown).
[0054] As shown in FIG. 4, device 400 rests on ledge 418 of housing
420 disposed towards the interior, and situated along the lower
portion, of housing wall 422 of housing 420. Outer housing 416,
which may comprise a variety of shapes and configurations,
variously helps to provide an attachment, anchoring or containment
point for electrical leads 414. According to one embodiment of the
invention, electrical leads 414 may comprise a spring clip.
According to another embodiment of the invention, electrical leads
414 may further comprise a bead, tab, hook or like feature for
engaging outer housing 416 (not illustrated). Note that housing 420
is in continuous and intimate contact with the heater and porous
member components of device 400 along housing wall 422.
[0055] Turning now to device 500 illustrated in FIG. 5, it should
be noted that the overall configuration of housing 420 differs
slightly from that shown for device 400 in FIG. 4. In FIG. 5,
housing walls 422 of housing 420 are disposed at a distance
somewhat remote from the porous member and heater components of
500, resulting in the inclusion of an opening or gap 524
therebetween. While the remaining features of device 500 are
relatively similar to those described previously for device 400, it
should be noted that the inclusion of gap 524 has surprisingly
afforded significant advantages in operability and longevity for
device 500 over device 400 and similar capillary force vaporizers
of the prior art, as described above.
[0056] Also somewhat surprisingly, it has been learned that gap 524
need not be very large in order to impart significant operating
enhancements to a CFV as compared devices that lacks a gap. Thus, a
gap comprising a total spacing of between approximately 3 mm,
preferably 2 mm, and most preferably 1 mm between a CFV and housing
wall 422 has been found to be adequate for those applications in
which housings are needed, used or desired. If the gap is too
large, there tends to be insufficient surface tension of the
bubbles that may arise from within the CFV. The result is that the
bubbles are unable to bridge gap 524 between the CFV and housing
wall 422. This can result in a tendency for feed liquid to leak out
of the device if placed in an inverted position, especially where
water is the liquid feed.
[0057] While gap 524 is shown schematically in FIG. 5, it should be
recognized that no one particular shape or configuration of spacing
between a CFV and housing wall is contemplated, and the shape,
placement and dimensions of gap 524 in FIG. 5 are for purposes of
illustration only. In fact, a number of different configurations
have been tried and evaluated. If viewed from above the CFV, that
is, along an imaginary line in the plane of the paper from the top
to the bottom of the illustration in. FIG. 5, the configuration can
best be described as: concentric circles; a circular array of 3 or
4 channels similar to a 3- or 4-leafed clover; a circular array
comprised of many channels; and so forth. According to a preferred
embodiment of the present invention, housing wall 422 and gap 524
are disposed in concentric configuration about a central CFV
device, respectively.
[0058] An alternate embodiment for a CFV is illustrated at 600 in
FIG. 6. This device differs from 500 in FIG. 5 in that housing wall
622 is shorter and therefore does not conceal or shield as much of
the CFV as compared to housing wall 422 of FIG. 5. In such a
configuration, there is less of a gap and more of the porous
member, comprising optional vaporizer 402 and insulator 404 are
exposed to the atmosphere. The result is that there are less
bubbles to collect, as they may freely emanate from the device.
[0059] In the extreme case, housing wall 622 can have a null
height. That is, housing 420 may comprise a disk with ledge 418
upon which a CFV is situated. In such a case, there is no gap, and
the CFV has an essentially infinitely open configuration. The only
requirement in this case is that there be some point of attachment
or anchor means for providing the necessary mechanical force to
hold the various CFV components together. In light of the foregoing
discussions, therefore, and according to one embodiment of the
present invention, a device for the generation of pressurized vapor
from unpressurized liquid may comprise: [0060] a) a porous member
further comprising an insulator and an optional vaporizer,
including a surface for receiving the liquid and an area for the
pressurization of vapor that is produced from the liquid; [0061] b)
a heater for conveying heat to the porous member for vaporizing the
liquid, the heater further comprising an area for the collection of
vapor and at least one orifice for release of the vapor at a
velocity greater than zero; [0062] c) a retainer for situating the
heater in heat-exchanging contact with the porous member; and
[0063] d) optionally, a housing including a housing wall present at
a spacing of 3 mm, preferably 2 mm and most preferably 1 mm from
porous member, heater and retainer.
C. Gravity as Suitable Mechanical Force
[0064] It should be noted that in its simplest form, a CFV may be
regarded as comprising a porous member, a heater and a retainer or
mechanical force generator to place the heater and porous member in
intimate heat-exchanging contact with one another. The porous
member further comprises an insulator and an optional vaporizer and
the heater further comprises a vapor collection region and at least
one orifice for the release of vapor.
[0065] A variety of mechanical force generators or mechanical force
generating means have been discussed previously. See, for example,
co-pending and commonly assigned application for patent
PCT/US2006/018,696 filed 15 May 2006, which discusses mechanical
force generation means such as clamping, springs, clips, etc. In
addition to the foregoing, during the course of the present
investigation, it was also surprisingly learned that even gravity
as in the gravitational force present on or in proximity to the
planet Earth, may provide a suitable mechanical force under certain
conditions for successful operation of a CFV. Accordingly, in one
embodiment of the present invention, a capillary force vaporizer
may comprise: [0066] a) a porous member, further comprising an
insulator and an optional vaporizer; [0067] b) a heater; and [0068]
c) a retainer for situating the heater in heat-exchanging contact
with the porous member;
[0069] wherein the retainer may be selected from among: the
gravitational force of the earth; tensioning devices such as spring
clips, clamps and clamping devices; friction fittings; snap
closures; bayonet attachments; threaded screw closures; twist-lock
closures; as well as the various types of spring systems known to
those skilled in the art, including conical washers, wavy washers,
bent leaf springs and coil springs; welding; chemical, physical or
mechanical bonding; sintering; glazing; chemical reaction; as well
as combinations of any of the foregoing.
D. Operation of CFVs at Higher Ambient Pressures
[0070] During typical CFV operation, capillary forces transport a
liquid feed towards a heat source, which vaporizes the liquid such
that it is emitted from the CFV at or slightly above atmospheric
pressure. Providing that the air or other ambient environment into
which the CFV was placed and operated was at or near atmospheric
pressure, the CFV device functioned normally. However, if the CFV
was operated in elevated atmospheres, back pressure on the CFV
device would ultimately drive the feed liquid back into the device
and prevent the successful emission of vaporized liquid.
[0071] Somewhat surprisingly, it has now been found that under
certain conditions, it is possible to generate pressurized vapor
using a CFV and to eject that vapor into a vapor stream, even one
at elevated pressures, without flooding or failure of the CFV
device. The key to achieving this goal is to ensure that there is
no pressure drop across the CFV device. However, the accomplishment
of this task turned out to be less than completely
straightforward.
[0072] Through attempts to operate a CFV in certain pressurized
environments, it was learned that the encounter of sufficient
backpressure would prevent the ejection of vapor and result in the
occasional flooding of the CFV. Although the capillary forces
acting on liquid feeds in the CFV were enough to deliver material
for vaporization into atmospheric environments, there was too much
of a pressure drop if the vapor was intended for use in pressurized
environments. Attempts to overcome the backpressure problem by mere
pressurization of the liquid feed, however, often resulted in too
much liquid being driven through the CFV such that large, visible
droplets of the liquid feed could be seen dripping at the
orifice(s) of the CFV device.
[0073] Interestingly, it was learned that by pressurizing the
liquid feed to approximate that of the ambient environmental
pressure as closely as possible, it was possible to operate the CFV
in order to generate vapor that would not be overwhelmed by the
carrier or environmental pressure. According to an embodiment of
the present invention, therefore, an apparatus for the generation
of a vapor jet from a liquid for use in an environment having
pressure at a first pressure above atmospheric pressure comprises:
[0074] a) a porous member including a surface for receiving the
liquid and an area for the pressurization of vapor that is produced
from the liquid; and [0075] b) a heater for conveying heat to the
porous member for vaporizing the liquid, the heater further
comprising an area for the collection of vapor and at least one
opening for release of the vapor at a velocity greater than zero;
[0076] wherein the liquid is present at a pressure of at least that
of the first pressure.
[0077] Similarly, a technique for the generation of pressurized
vapor in environments having pressures at a first pressure above
atmospheric pressure can be contemplated as comprising the steps
of: [0078] a) pressurizing a source of liquid feed to a second
pressure; and [0079] b) providing the pressurized liquid feed to a
capillary force vaporizer, the capillary force vaporizer
comprising: [0080] i) a porous member further comprising an
insulator including a surface for receiving the liquid feed and an
optional vaporizer, including a vaporization area for the
collection and pressurization of vapor that is produced from the
liquid; and [0081] ii) a heater component for conveying heat to the
porous member for the vaporization of the liquid and at least one
opening for release of the vapor at a velocity greater than
zero;
[0082] wherein the second pressure is at least equal to the first
pressure.
It should be noted that it is not necessary to pressurize liquid
feed to a CFV that is operating at or near atmospheric pressure.
Thus, small variations in atmospheric or environmental pressure can
be handled by the CFV without compromising the operation of the CFV
device.
[0083] The present invention has been described above in detail
with reference to specific embodiments, Figures, and examples.
These embodiments, Figures and examples should not be construed as
narrowing the scope of the invention, but rather serve as
illustrative examples to facilitate an understanding of the
invention and ways in which the invention may be practiced, and to
further enable those of skill in the pertinent art to practice the
invention. It is to be further understood that various
modifications and substitutions may be made to the described
capillary force vaporizer devices, modules and systems, as well as
to materials, methods of manufacture and use, without departing
from the broad scope of the invention contemplated herein. The
invention is further illustrated and described in the claims that
follow.
* * * * *