Disclosed is a multi-staged desiccant refrigeration device which
employs an evaporator combined with a multi-staged vapor desiccant/heat
sink module which absorbs water vapor from the evaporator. A plurality
of stage vapor desiccant/heat desiccant modules are incorporated
in the device, the automatic staged opening and closing of the modules
allowing for a continuous and more efficient refrigeration process.
What is claimed is:
1. A refrigeration apparatus, comprising:
a refrigerant chamber containing an evaporatable refrigerant liquid;
a plurality of desiccant chambers, each containing a sorbent material
for said liquid;
at least one conduit for conducting vaporized refrigerant liquid
to said chambers; and
one or more valving means for directing said vapor to each said
chamber in sequence, so that sorbent in a first such chamber contacts
said vapor first, until at least a portion of the sorptive capacity
of the sorbent in the first chamber is exhausted, and then a first
said valving means directs said vapor into a second such chamber
in response to a temperature of the first chamber.
2. The apparatus of claim 1 wherein said valving means open when
they attain a predetermined temperature.
3. The apparatus of claim 2 wherein said valving means opened
by the melting of a phase change material.
4. The apparatus of claim 3 wherein said phase change material
is a wax.
5. The apparatus of claim 4 wherein said wax is a paraffin wax.
6. The apparatus of claim 1 wherein a second said valve directs
said vapor into a third such chamber after at least a portion of
the sorptive capacity of sorbent in said second chamber is exhausted.
7. The apparatus of claim 1 wherein said refrigerant chamber contains
a wicking material adapted to increase the surface area from which
evaporation of said liquid can take place.
8. The apparatus of claim 7 wherein said wicking material lines
the interior surface of said refrigerant chamber.
BACKGROUND OF THE INVENTION
The vapor pressure of refrigerants, particularly water, decreases
as the temperature decreases, so that the operating pressure is
small near the end of discontinuous refrigerant operation.
Vapor desiccants also have higher vapor pressures at higher temperatures
and thus have a decreasing capacity for water vapor as the temperature
of the system increases.
Therefore, as the cooling process proceeds in a conventional desiccant
refrigeration system, the available vapor supply pressure falls,
the vapor absorption pressure rises and the capacity of the desiccant
decreases, so the characteristics of the evaporation and the desiccant/heat
sink portions of the system are not ideally matched. This inequality
provides the principal limitation on minimizing the size of such
a refrigerant system, and contributes to the time required to cool
the system to the designed temperature.
If a portion of the released heat is transferred to a heat sink
material, the desiccant temperature is lessened, so that the desiccant
can absorb more water vapor. There is an optimum choice of ratio
of heat sink mass-desiccant mass which for a given combination of
materials gives a minimum total mass and volume for a given short
time water absorption which can be determined easily.
Three physical characteristics affect the amount of water vapor
which a desiccant can absorb in a short period of time.
The first characteristic is the relationship between desiccant
water vapor capacity and desiccant temperature. The amount of water
which all common desiccants can contain decreases with temperature
due to their decreasing capacity for water vapor due to their higher
vapor pressure at higher temperatures.
The second characteristic which affects performance of the desiccant
is the amount of chemical reaction energy released when the water
is bound into the desiccant. Any water vapor absorption process
releases the latent heat of vaporization of the water into the desiccant
when the molecule is bound into the desiccant structure of molecular
However, most desiccants also react chemically with the water in
an exothermic process. Two commercially available desiccants, Drierite
(a calcium sulphate desiccant available from W.A. Hammond Drierite
Co. Xenia, OH and Multiform molecular sieve 4A, (a synthetic zeolite
molecular sieve available from Multiform Desicants, Inc., Buffalo,
New York) exhibit an exothermic chemical reaction when reacting
with water. In the case of the Multiform desiccant, the reaction
heat is 80% of the water vapor latent heat. Therefore, 1.8 calories
of heat are released into the desiccant for every calorie of heat
absorbed from the cooled material in the refrigerator evaporator.
The final characteristic is the vapor pressure over the desiccant
in a conventional single-use desiccant refrigerator apparatus. In
such an apparatus, the desiccant is analogous to both the pump and
condenser found in the conventional refrigeration cycle. This value,
which increases with temperature, is equivalent to the suction pressure
in a compressor refrigerant process at the refrigerator compressor
This increased pressure (reduced suction) reduces the refrigeration
efficiency of the apparatus as the single-use, non-cyclical desiccant
refrigeration process proceeds. As the temperature of the material
being cooled falls, the refrigerant (e.g. evaporating water) vapor
pressure decreases, thereby reducing the pressure of the vapor supplied
to the desiccant. Simultaneously, the temperature of the desiccant
rises, thereby increasing the vapor pressure of the desiccant and
water absorption rises so that vapor flow from water to desiccant
becomes small. Conventional desiccant refrigerant devices have not
breached the issue of modifying the evaporator pressure decrease
with decreasing temperature.
SUMMARY OF THE INVENTION
The present invention relates to a desiccant refrigeration device
employing an evaporator combined with a multi-staged vapor desiccant-heat
sink module to absorb water vapor from the beverage cooler. The
refrigeration device consists of a plurality of staged vapor desiccant-heat
desiccant modules, so that the desiccants and heat sinks can be
employed to higher temperatures during the early part of the cooling
process where evaporator pressures are high, and are then valved
off at the same time a fresh desiccant section is exposed, thereby
more closely matching the requirements of the evaporator and providing
a continuous refrigerating process.
Thus, the present invention provides a refrigeration apparatus,
comprising a refrigerant chamber containing an evaporatable refrigerant
liquid, a plurality of desiccant chambers, each containing a sorbent
material for the liquid, at least one conduit for conducting vaporized
refrigerant liquid to the chambers, and one or more valves for directing
the vapor to each the chamber in sequence, so that sorbent in a
first such chamber contacts the vapor first, until at least a portion
of the sorptive capacity of the sorbent in the first chamber is
exhausted, and then a first the valve directs the vapor into a second
such chamber. In one embodiment, the valves open when they attain
a predetermined temperature. Preferably, the valves are opened by
the melting of a phase change material which can be a wax such as
In a preferred embodiment, a second valve directs the vapor into
a third chamber after at least a portion of the sorptive capacity
of sorbent in the second chamber is exhausted.
In another variation of the apparatus, the refrigerant chamber
contains a wicking material adapted to increase the surface area
from which evaporation of the liquid can take place. The wicking
material preferably lines the interior surface of the refrigerant
Also provided by the present invention is a method for facilitating
the effective sorption of a refrigerant vapor by a sorbent in a
refrigeration apparatus, comprising the steps of directing refrigerant
vapor into a first mass of sorbent material until at least a portion
of the sorptive capacity thereof is exhausted, and then directing
the refrigerant vapor into a second mass of sorbent material. The
method may also include the steps of continuing to direct the refrigerant
material into the second mass of sorbent material until at least
a portion of the sorptive capacity of the second mass is exhausted,
and then directing the refrigerant vapor into a third mass of sorbent
In one embodiment, the masses of desiccant material are in separate
chambers, and the directing steps are accomplished by opening valves
to permit the vapor to contact the masses. Preferably, at least
one of the valves is opened in response to temperature, and may
be opened by the melting of a phase change material, such as a paraffin
In another embodiment, the method includes the step of generating
the refrigerant vapor in a refrigerant chamber having a wicking
material therein by permitting at least a portion of the refrigerant
to evaporate from the wicking material. Preferably, the wicking
material lines the interior of the refrigerant chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side elevation of the present invention which
reveals the contents of the evaporation and desiccant chambers in
a cut-away manner.
FIG. 2 is a schematic cross section a particular embodiment of
the multi-staged desiccant system of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 the refrigeration device 10 of the present invention
has a refrigerant chamber 12 which may advantageously be lined
on the interior surface 14 with a wicking material 16. In a preferred
embodiment, the wicking layer may be applied by flocking the interior
surface 14 with the wicking material 16. The refrigerant chamber
12 is filled with a refrigerant liquid 18 such as water.
The refrigerant device 10 has associated with it a desiccant system
40 comprising a desiccant chamber 20 divided into a plurality of
desiccant modules 51 57 63 66. In one preferred embodiment, the
chamber 20 surrounded by a thermal insulator 22 and is at least
partially filled with a desiccant 24. Furthermore, the desiccant
may be in contact with a heat removing material 25 as disclosed
in our U.S. Pat. No. 4759191. Separating the individual modules
are a series of valves 54 60 61.
At least the first desiccant module 51 of the desiccant chamber
20 is initially evacuated, and, preferably, all of the desiccant
modules are initially evacuated. In addition, the refrigerant chamber
may also advantageously be evacuated to the extent that it contains
substantially only the vapor of the refrigerant liquid.
Connecting the refrigerant and desiccant chambers 12 and 20 is
a conduit 28 and a valve 30 interposed in the conduit 28 allowing
fluid communication between the chambers 12 and 20 through the conduit
28 only when the valve 30 is open.
The operation of the cooling device 10 is suspended (i.e., the
system is static and no cooling occurs) until the valve 30 is opened,
at which time the conduit 28 permits fluid communication between
the refrigerant and chambers 12 and the first desiccant module 51
of the desiccant chamber 20. Opening the valve 30 between the refrigerant
and desiccant chambers causes a drop in pressure in chamber 12 because
the first desiccant module 51 of the desiccant chamber 20 is evacuated.
The drop in pressure in the refrigerant chamber 12 upon opening
of the valve 30 causes the liquid 18 to boil at ambient temperature
into a liquid-vapor mixture 32.
This liquid-to-gas phase change can occur only if the liquid 18
removes heat equal to the latent heat of vaporization of the evaporated
liquid 18 from the refrigerant chamber 12. This causes the refrigerant
chamber 12 to cool. The cooled refrigerant chamber 12 in turn,
removes heat from its surrounding material, as indicated by the
The liquid-vapor mixture 32 is directed through a liquid-vapor
collector and separator 34 of conventional design, which separates
any entrained liquid 18 from the vapor, allowing the separated liquid
18 to return to the refrigerant chamber 12 through the liquid return
line 38 and allowing the vapor to pass through the conduit 28 into
the desiccant chamber 20 flowing into the first desiccant module
51. Once inside the first desiccant module 51 the vapor is absorbed
or adsorbed by the desiccant 24. This facilitates the maintenance
of a reduced vapor pressure in the refrigerant chamber 12 and allows
more of the liquid 18 to boil and become vapor, further reducing
the temperature of chamber 12.
The continuous removal of the vapor maintains the pressure in the
refrigerant chamber 12 below the vapor pressure of the liquid 18
so that the liquid 18 boils and produces vapor continuously until
desiccant 24 is saturated within the first desiccant module 51
or, alternatively, there is a reduction in the cooling capacity
of the refrigerant chamber. In order to continue the refrigeration
process at this point by keeping the vapor pressure of the desiccant
24 low, a new section of desiccant 24 must be exposed to the vapor.
To provide this function, a valve 54 is disposed between the first
desiccant module 51 and the second desiccant module 57.
The valve is preferably sensitive to either the temperature within
the first desiccant module at the time the desiccant is saturated;
the temperature or vapor supply pressure entering the first desiccant
module which indicates an increase in the vapor pressure of the
desiccant; or, alternatively, any change in temperature or vapor
pressure which would indicate a reduction in the refrigerating efficiency
of the cooling device 10.
Paraffin waxes with melting temperatures ranging from below 100
degrees (F) to over 250 degrees (F), are known in the art. Such
waxes may be advantageously used to comprise the valves 54 60
61 of the invention to automatically melt at a preselected temperature
and thereby provide communication between the desiccant modules.
Other conventional materials having selected melting points could
also be used for the valve 54.
At that point in time, the wax valve 54 melts and allows fluid
communication between the first desiccant module 51 and the second
desiccant module 57. The melting of the wax valve between the first
desiccant module 51 and the second desiccant module 57 will preferably
coincide with either the temperature of the first desiccant module
51 at the time the desiccant 24 is saturated, or a temperature producing
a reduction of vapor supply pressure from the refrigerant chamber
12 indicating a reduction in the refrigerant efficiency of the
cooling device 10.
The vapor then flows into the second desiccant module 57 and is
absorbed or adsorbed by the desiccant 24 contained within the second
desiccant module 57. The continuous removal of the vapor into the
second desiccant module 57 will maintain the pressure in the refrigerant
chamber 12 below the vapor pressure of the liquid 18 so that the
liquid 18 continues to boil and produce vapor continuously until
the desiccant 24 within the second desiccant module 57 is saturated.
At this point in time, the second wax valve 60 melts to provide
communication between the second desiccant module 57 and the third
desiccant module (depicted in phantom at 63) under the conditions
described above, thereby continuing the refrigerant process of the
cooling device 10. This process continues sequentially until the
vapor reaches the last desiccant module of the chamber 20 (depicted
in phantom at 66), the refrigerant process preferably continuing
until the liquid 18 has boiled away, or until the temperature of
the liquid 18 has dropped below its boiling point at the existing
pressures within the refrigerant chamber 12.
During the vaporization process, the level of the liquid 18 in
the refrigerant chamber 12 drops. The wicking material 16 retains
the liquid 18 on the interior surface 14 of the refrigerant chamber
12 to prevent a reduction in the area of contact between the liquid
18 and the interior surface 14 which would cause a reduction in
the effective heat transfer surface area of the refrigerant chamber
12 and would thus slow the cooling process.
When the desiccant 24 absorbs or adsorbs the vapor, a heat of absorption
or adsorption is generated. The heat removing material 25 which
is thermally coupled to the desiccant 24 (and preferably is mixed
with the desiccant 24) removes heat from the desiccant 24 preventing
or slowing a rise in temperature in both desiccant 24 and chamber
20 which rise in temperature might compromise the cooling effect
produced by chamber 12. Tests have shown that paraffin waxes which
are readily available and accepted for food use are not only useful
as heat sink materials, but have a low enough vapor pressure that
they need not be sealed when used in an operational beverage cooler,
even when in the molten state. These waxes wet most of the desiccant
24 quickly in the molten state. They can therefore be used to seal
the desiccant at the end of their usefulness.
Thus, the multi-staged desiccant refrigeration device 10 of the
instant invention arranges the desiccant-heat sink system 40 so
that the average vapor pressure of the desiccant system throughout
the refrigerating process remains low. To perform this function,
the desiccant system 40 utilizes the plurality of separately valved,
isolated desiccant modules 51 57 63 66. These desiccant modules
function so that when the vapor pressure of the desiccant rises
in one module by a rise in temperature of the desiccant, that module
automatically closed off and another, which has not yet been exposed
to vapor, automatically opened, thereby retaining a constant vapor
flow between refrigerant and desiccant by keeping the vapor pressure
of the desiccant low. Such a procedure would be useful for applications
in which minimizing and sustaining the cooling time is important,
such as in a beverage cooling application.
Although the average cooling rate can be increased by such staging,
the overall total heat absorption capability generally remains unchanged,
since total vapor absorbed as compared with a conventional device
and total resulting heat deposition in the desiccant-heat sink module
remain unmodified. However, other methods or materials optimizing
these conditions may advantageously be used with the device.
As is shown in FIG. 1 the aforementioned configuration allows
the construction of the cooling device 10 to be miniaturized and
compact. Its size can be greatly reduced by placing the plurality
of desiccant modules in a space-conserving configuration, as depicted
in FIG. 2.
An alternative embodiment of the desiccant chamber 70 is depicted
in FIG. 2. The desiccant chamber 70 comprises a first desiccant
module 73 a second desiccant module 75 and a third desiccant module
78 disposed in a circular configuration, surrounded in a preferred
embodiment by a thermal insulator 20 which is at least partially
filled with a desiccant 24 in contact with a heat removing material
Again, as described above, the desiccant modules 73 75 78 are
initially evacuated. Surrounding the structure of the desiccant
chambers is a chamber 81 into which vapor from the refrigerant chamber
12 (not shown) is conducted. The chamber 81 may be evacuated advantageously
to the extent it allows for flow of vapor from the refrigerant chamber
to the desiccant chamber 70. Surrounding the chamber 81 is a thermal
insulator 83 which retards the dissipation of heat from the desiccant
chamber 70. A channel 85 is disposed around the modules 73 75
78 preferably located between the thermal insulator 20 and the
modules, to provide vapor communication between the first module
73 and the second module 75 and the second module 75 and the third
The multiple module desiccant chamber 70 of the instant invention
is operated similarly to that described in FIG. 1 wherein the operation
of the desiccant chamber is suspended until the valve 30 is open
(not shown) at which time the conduit provides fluid communication
between the refrigerant chamber (not shown) and the vapor chamber
81 allowing vapor flow from the refrigerant chamber to extend throughout
the area of the chamber 81. At this point in time, the trigger valve
88 is opened, causing a drop in pressure in module 73 as the module
chamber 73 is evacuated. The opening of the valve 88 allows vapor
to pass into the first desiccant module 73. Once inside the first
desiccant module 73 the vapor is absorbed or adsorbed by the desiccant
Again, this facilitates the maintenance of the reduced vapor pressure
in the refrigerant chamber (not shown) and allows more liquid contained
therein to boil and become vapor, further reducing the temperature
of the refrigerant chamber.
As previously discussed, the continuous removal of vapor maintains
the pressure in the refrigerant chamber below the vapor pressure
of the liquid, so that the liquid boils and produces vapor continuously
until the desiccant 24 is saturated within the first desiccant module
73. Thus, the first wax valve 90 melts and allows fluid communication
through conduit 85 between the first desiccant module 73 and the
second desiccant module 75. As the second desiccant module 75 is
evacuated, the opening of the valve 90 draws the vapor flow from
the refrigerant chamber, through the first desiccant module 73 and
into the second desiccant module 75 thereby continuing the cooling
The melted wax from the wax valves separating the desiccant modules
73 75 and 78 may serve a dual purpose. After melting, the wax
may be used to seal the desiccant after its usefulness, i.e., after
the vapor pressure of the desiccant reaches a designated level.
Again, the melting of the wax valve 90 between the first desiccant
module 73 and the second desiccant module 75 preferably coincides
with either the temperature of the first desiccant module at the
time the desiccant is saturated, or, alternatively, a temperature
producing a reduction of vapor supply pressure from the refrigerant
chamber indicating a reduction in the refrigerant efficiency of
the cooling device.
The vapor then flows within the second desiccant module 75 and
is thus absorbed or adsorbed by the desiccant 24 contained within
the second desiccant module 75. Again, the second desiccant module
75 continues to absorb the water vapor until the desiccant 24 within
it is saturated, at which point in time the second wax valve 9 melts
at the designated temperature to provide fluid communication between
the second desiccant module 75 and the third desiccant module 78
through surrounding conduit 85. As previously explained, the melting
of the second wax valve 92 may also serve to seal off the desiccant
24 contained within the second desiccant module 75. As before, the
evacuated third desiccant module 78 when breached by the melting
of the second wax valve 92 creates a negative pressure which produces
a flow of the vapor through the first and second modules into the
third desiccant module. The cooling process continues as previously
stated, until the liquid 18 has boiled away or until the temperature
of the liquid has dropped below its boiling point.
The present invention may consist of any of a number of desiccant
modules, the number of modules and their desiccant capacity preferably
dependent upon and matched with the refrigerant capacity of the
liquid refrigerant used in the system.
Three important components of the present invention are the evaporating
liquid, the desiccant and the heat removing material. The liquid
and the desiccant must be complimentary (i.e., the desiccant must
be capable of absorbing or adsorbing the vapor produced by the liquid),
and suitable choices for these components would be any combination
able to make a useful change in temperature in a short time, meet
government standards for safety and be compact.
The refrigerant liquids used in the present invention preferably
have a high vapor pressure at ambient temperature, so that a reduction
of pressure will produce a high vapor production rate. The vapor
pressure of the liquid at 20.degree. C. is preferably at least about
9 mm Hg, and more preferably is at least about 15 or 20 mm Hg. Moreover,
for some applications (such as cooling of food products), the liquid
should conform to applicable government standards in case any discharge
into the surroundings, accidental or otherwise, occurs. Liquids
with suitable characteristics for various uses of the invention
include: various alcohols, such as methyl alcohol and ethyl alcohol;
ketones or aldehydes, such as acetone and acetaldehyde; water; and
freons, such as freon C318 114 21 11 114B2 113 and 112. The
preferred liquid is water.
In addition, the refrigerant liquid may be mixed with an effective
quantity of a miscible nucleating agent having a greater vapor pressure
than the liquid to promote ebullition so that the liquid evaporates
even more quickly and smoothly, and so that supercooling of the
liquid does not occur. Suitable nucleating agents include ethyl
alcohol, acetone, methyl alcohol, propyl alcohol and isobutyl alcohol,
all of which are miscible with water. For example, a combination
of a nucleating agent with a compatible liquid might be a combination
of 5% ethyl alcohol in water or 5% acetone in methyl alcohol. The
nucleating agent preferably has a vapor pressure at 25.degree. C.
of at least about 25 mm Hg and, more preferably, at least about
35 mm Hg. Alternatively, solid nucleating agents may be used, such
as the conventional boiling stones used in chemical laboratory applications.
The desiccant material used in the desiccant chamber 21 is preferably
capable of absorbing and adsorbing all the vapor produced by the
liquid, and also preferably will meet government safety standards
for use in an environment where contact with food may occur. Suitable
desiccants for various applications may include barium oxide, magnesium
perchlorate, calcium sulfate, calcium oxide, activated carbon, calcium
chloride, glycerine, silica gel, alumina gel, calcium hydride, phosphoric
anhydride, phosphoric acid, potassium hydroxide, sulfuric acid,
lithium chloride, ethylene glycol and sodium sulfate.
The heat-removing material may be one of three types: (1) a material
that undergoes a change of phase when heat is applied; (2) a material
that has a heat capacity greater than the desiccant; or (3) a material
that undergoes an endothermic reaction when brought in contact with
the liquid refrigerant.
Suitable phase change materials for particular applications may
be selected from paraffin, naphthalene, sulphur, hydrated calcium
chloride, bromocamphor, cetyl alcohol, cyanamide, eleudic acid,
lauric acid, hydrated sodium silicate, sodium thiosulfate pentahydrate,
disodium phosphate, hydrated sodium carbonate, hydrated calcium
nitrate, Glauber's salt, potassium, sodium and magnesium acetate.
The phase change materials remove some of the heat from the desiccant
material simply through storage of sensible heat. In other words,
they heat up as the desiccant heats up, removing heat from the desiccant.
However, the most effective function of the phase change material
is in the phase change itself. An extremely large quantity of heat
can be absorbed by a suitable phase change material in connection
with the phase change (i.e., change from a solid phase to a liquid
phase, or change from a liquid phase to a vapor phase). There is
typically no change in the temperature of the phase change material
during the phase change, despite the relatively substantial amount
of heat required to effect the change, which heat is absorbed during
the change. Phase change materials which change from a solid to
a liquid, absorbing from the desiccant their latent heat of fusion,
are the most practical in a closed system. However, a phase change
material changing from a liquid to a vapor is also feasible. Thus,
an environmentally-safe liquid could be provided in a separate container
(not shown) in contact with the desiccant material (to absorb heat
therefrom) but vented in such a way that the boiling phase change
material carries heat away from the desiccant material and entirely
out of the system.
Another requirement of any of the phase change materials is that
they change phase at a temperature greater than the expected ambient
temperature of the material to be cooled, but less than the temperature
achieved by the desiccant material upon absorption of a substantial
fraction (i.e., one-third or one-quarter) of the refrigerant liquid.
Thus, for example, in most devices according to the present invention
which are intended for use in cooling a material such as a food
or beverage, the phase change material could change phase at a temperature
above about 30.degree. C., preferably above about 35.degree. C.
but preferably below about 70.degree. C., and most preferably below
about 60.degree. C. Of course, in some applications, substantially
higher or lower phase change temperatures may be desirable. Indeed,
many phase change materials with phase change temperatures as high
as 90.degree. C., 100.degree. C. or 110.degree. C. may be appropriate
in certain systems.
Materials that have a heat capacity greater than that of the desiccant
simply provide a thermal mass in contact with the desiccant that
does not effect the total amount of heat in the system, but reduces
the temperature differential between the material being cooled and
the desiccant chamber, with two results. First, the higher the temperature
gradient between two adjacent materials, the more rapid the rate
of heat exchange between those two materials, all else being equal.
Thus, such thermal mass materials in the desiccant chamber slow
the transfer of heat out of the desiccant chamber. Second, many
desiccant materials function poorly or do not function at all when
the temperature of those materials exceeds a certain limit. Heat-absorbing
material in the form of a thermal mass can substantially reduce
the rate of the desiccant's temperature increase during the cooling
cycle. This, in turn, maintains the desiccant at a lower temperature
and facilitates the vapor-sorption capabilities of the desiccant.
Various materials which have a high specific heat include cyanamide,
ethyl alcohol, ethyl ether, glycerol, isoamyl alcohol, isobutyl
alcohol, lithium hydride, methyl alcohol, sodium acetate, water,
ethylene glycol and paraffin wax.
Care must be taken, of course, when selecting a high specific heat
material (or high thermal mass material) to ensure that it does
not interfere with the functioning of the desiccant. If the heat-absorbing
material, for example, is a liquid, it may be necessary to package
that liquid or otherwise prevent physical contact between the heat-absorbing
material and the desiccant. Small individual containers of heat-absorbing
material scattered throughout the desiccant may be utilized when
the desiccant and the heat-absorbing material cannot contact one
another. Alternatively, the heat-absorbing material may be placed
in a single package having a relatively high surface area in contact
with the desiccant to facilitate heat transfer from the desiccant
into the heat-absorbing material.
The third category of heat-removing material (material that undergoes
an endothermic reaction) has the advantage of completely removing
heat from the system and storing it in the form of a chemical change.
The endothermic material may advantageously be a material that undergoes
an endothermic reaction when it comes in contact with the refrigerant
liquid (or vapor). In this embodiment of the invention, when the
valve 30 in the conduit 28 is opened, permitting vapor to flow through
the conduit 28 into the third chamber 21 the vapor comes in contact
with some of the endothermic material, which then undergoes an endothermic
reaction, removing heat from the desiccant 24. Such endothermic
materials have the advantage that the heat is more or less permanently
removed from the desiccant, and little, if any, of that heat can
be retransferred to the material being cooled. This is in contrast
to phase change materials and materials having a heat capacity greater
than the desiccant material, both of which may eventually give up
their stored heat to the surrounding materials, although such heat
exchange (because of design factors that retard heat transfer, such
as poor thermal conductivity of the desiccant 24) generally does
not occur with sufficient rapidity to reheat the cooled material
prior to use of that material.
Heat-absorbing materials which undergo an endothermic reaction
may variously be selected from such compounds as H.sub.2 BO.sub.3
PbBr.sub.2 KBrO.sub.3 KClO.sub.3 K.sub.2 Cr.sub.2 O.sub.7 KClO.sub.4
K.sub.2 S, SnI.sub.2 NH.sub.4 Cl, KMnO.sub.4 and CsClO.sub.4. Furthermore,
the heat-removing material may be advantageously in contact with
the desiccant. In various embodiments of the invention, the desiccant
and heat-removing material could be blended, the heat-removing material
could be in discrete pieces mixed with the desiccant, or the material
could be a mass in contact with, but not mixed into, the desiccant.
In selecting the wicking material 16 any of a number of materials
may be chosen, depending upon the requirements of the system and
the particular refrigerant liquid 18 being used. The wicking material
may be something as simple as cloth or fabric having an affinity
for the refrigerant liquid 18 and a substantial wicking ability.
Thus, for example, when the refrigerant liquid is water, the wicking
material may be cloth, sheets, felt or flocking material which may
be comprised of cotton, filter material, natural cellulose, regenerated
cellulose, cellulose derivatives, blotting paper or any other suitable
The most preferred wicking material would be highly hydrophilic,
such as gel-forming polymers which would be capable of coating the
interior surface of the evaporation chamber. Such materials preferably
consist of alkyl, aryl and amino derivative polymers of vinylchloride
acetate, vinylidene chloride, tetrafluoroethylene, methyl methacrylate,
hexanedoic acid, dihydro-25-furandione, propenoic acid, 13-isobenzofurandione,
1 h-pyrrole-25-dione or hexahydro-2 h-azepin-2-one.
The wicking material may be sprayed, flocked, or otherwise coated
or applied onto the interior surface of the refrigerant chamber
12. In a preferred embodiment, the wicking material is electrostatically
deposited onto that surface. In another embodiment, the wicking
material is mixed with a suitable solvent, such as a non-aqueous
solvent, and then the solution is applied to the interior surface
of the refrigerant chamber 12.
In another preferred embodiment, the wicking material is able to
control any violent boiling of the evaporator and thus reduces any
liquid entrainment in the vapor phase. In such an embodiment, the
wicking material is a polymer forming a porous space-filling or
sponge-like structure, and it may fill all or part of the refrigerant
The valve 30 may be selected from any of the various types shown
in the prior art. The valve 30 may be located at any location between
the refrigerant chamber 12 and the desiccant chamber 20 so long
as it prevents vapor from being sorbed by the desiccant 24. However,
if the entire device 10 is within a pressurized container, a pressure
responsive valve can be used which can actuate the cooling device
upon the release of the pressure within the container.
The invention also includes a method of using the cooling device
described herein. This method includes the step of providing a cooling
device of the type set forth herein; opening the valve between the
refrigerant chamber 12 and the desiccant chamber 20 whereby the
pressure in the refrigerant chamber is reduced, causing the liquid
to boil, forming a vapor, which vapor is collected by the desiccant
material; removing vapor from the desiccant chamber by collecting
the same in the desiccant until an equilibrium condition is reached
wherein the desiccant is substantially saturated or substantially
all of the liquid originally in the refrigerant chamber has been
collected in the desiccant; and simultaneously removing heat from
the desiccant by means of the heat-removing material described above.
The process is preferably a one-shot process; thus, opening of the
valve 30 in the conduit 28 connecting the refrigerant chamber 12
and the desiccant chamber 20 is preferably irreversible. At the
same time, the system is a closed system; in other words, the refrigerant
liquid does not escape the system, and there is no means whereby
the refrigerant liquid or the desiccant may escape either the refrigerant
chamber 12 or the desiccant chamber 20.
Although the invention has been described in the context of certain
preferred embodiments, it is intended that the scope of the invention
not be limited to the specific embodiment set forth herein, but
instead be measured by the claims that follow.