A rotary regenerative heat wheel having a heat exchange matrix
comprised of a spirally wound strip of plastic having a coating
of dry desiccant affixed thereto. The quantity of desiccant affixed
to the strip is selected so that the sensible and latent heat transfer
efficiencies of the wheel are relatively high and approximately
equal. An apparatus and method are disclosed for applying a desiccant
coating to a sheet of plastic.
What is claimed is:
1. A desiccant regenerative heat exchange device comprising at
least one plastic surface coated with finely comminuted particles
of dry desiccant bound to said at least one plastic surface as a
consequence of dissolving to a minor depth using a selected solvent
at least the portion of said at least one plastic surface contacting
2. A device according to claim 1 wherein said particles of dry
desiccant are bound directly to said at least one plastic surface.
3. A device according to claim 1 wherein said device comprises
at least one wound strip of plastic material having both surfaces
of said strip coated with said dessicant.
4. A device according to claim 3 wherein said device includes a
wheel, said wheel comprises a hub about which said strip is wound,
and a plurality of spokes affixed to said hub and extending from
said hub across said wound strip, said spokes being affixed along
their length to a surface of said wheel for transmitting driving
force from said hub to said wheel.
5. A device according to claim 3 wherein the average thickness
of said desiccant coating on each surface of said strip is between
about ten and thirty microns thick.
6. A device according to claim 3 wherein said strip has a plurality
of regularly distributed surface protrusions for separating adjoining
layers of said wound strip so as to permit the flow of atmospheric
gases between said layers.
7. A device according to claim 6 wherein said device includes
a second plastic strip wound with said first strip so that said
first and second strips from alternate layers on said wheel, said
second strip having both surfaces coated with said desiccant.
8. A device according to claim 7 wherein said second plastic strip
9. A device according to claim 3 wherein said particles are bound
to said surfaces so that only a small portion of the surface area
of each discrete desiccant particle is in contact with said strip.
10. A device according to claim 1 wherein said desiccant includes
dried silica gel.
11. A device according to claim 3 wherein said one plastic strip
is made from biaxially-oriented polystyrene.
12. A device according to claim 1 wherein said desiccant includes
dried alumina gel.
13. A device according to claim 1 wherein said desiccant particles
each have an average diameter of between approximately ten and thirty
14. A device according to claim 1 wherein said particles of dry
desiccant are bound to said one plastic surface without the use
of an adhesive substance.
15. A device according to claim 1 wherein said particles of dry
desiccant are embedded slightly in said one plastic surface.
16. A desiccant regenerative heat exchange device comprising at
least one plastic surface coated with finely comminuted particles
of dry desiccant bound directly to said at least one plastic surface,
wherein said particles of dry desiccant are bound to said one plastic
surface by means of a solvent bonding process.
17. A device according to claim 16 wherein said particles of dry
desiccant are embedded slightly in said one plastic surface.
This invention relates to rotary regenerative heat exchange devices
and, more particularly, to heat devices having both moisture exchange
and heat recovery capabilities.
The advent of increased fuel costs has resulted in greater efforts
to seal air leaks in homes and other human occupancies in order
to conserve energy. However, the reduction of natural ventilation
has resulted in poorer quality air in these structures. A study
by the National Institute of Health indicates that 50% of the illness
in the United States can be attributed to the poor quality of indoor
air. (See National Institute of Health Study "National Center
for Health Statistics", U.S. Department of Health and Human
Services, National Health Survey (Washington, D.C. 1981) As a consequence,
there exists a conflict between energy conservation measures and
human health factors that can best be resolved with energy efficient
Heat recovery devices, typically in the form of rotary air-to-air
heat exchangers, are well-known for their ability to transfer heat,
water vapor, or both between incoming and outgoing ventilation airstreams
so as to conserve energy, while at the same time improving the quality
of the indoor air. Passages formed in the media comprising the heat
exchange matrix permit passage of gases through the wheel. Use of
these devices in ventilating, heating and/or air conditioning systems
can reduce heating and cooling costs, while providing fresh outdoor
air to lower internal air pollution levels. For regenerative devices
of the rotary wheel type, the incoming airstream is directed through
one sector of the slowly revolving wheel while an outgoing airstream
is directed through another sector of the wheel. Heat and moisture
are simultaneously absorbed from the warmer airstream at the one
sector and removed from the wheel by the cooler, dryer airstream
at the other sector. For stationary periodic flow regenerators,
the airstream is alternately directed through the entire exchange
device first in one direction and then in the opposite direction.
Known heat transfer devices have been described as falling into
one of three categories: (1) those designed primarily for the removal
of sensible heat, (2) those designed primarily for the removal of
latent heat, and (3) those designed to remove both sensible and
latent heat, the so-called "enthalpy exchangers". Examples
of sensible heat wheels of the first category are disclosed in U.S.
Pat. Nos. 2563415 and 4432409. Examples of latent heat wheels
of the second category are disclosed in U.S. Pat. Nos. 2700577
and 3176446. Examples of enthalpy exchangers are disclosed in
U.S. Pat. Nos. 3307617 3664095 3733791 4172164 and 4255171.
The sensible and latent wheels of the first and second categories
are limited in their application since they primarily perform only
a single exchange function. With increasing fuel costs, exchange
of both latent and sensible heat is desired for ventilation air.
The choice of media comprising the heat exchange matrix of the
device must be suitable for application in ventilation systems for
houses, offices, and other human dwellings. For example, the use
of asbestos, as disclosed in U.S. Pat. No. 3307617 for the exchange
media is undesirable.
To maximize the benefit of operating an air exchanger in conjunction
with a ventilating, heating and/or cooling system, it is desirable
to choose as the heat exchange matrix, a material capable of providing
high sensible and latent heat exchange efficiencies. The use of
metal, wool, uncoated metal strips, certain coated Kraft papers,
and other fibrous cellulose materials tend to be unsatisfactory
because the latent heat exchange efficiency of these materials is
relatively poor, as compared to the sensible heat exchange efficiency.
Several of the prior art wheels coat a "liquid" desiccant,
such as lithium chloride or calcium chloride, onto the heat exchange
matrix. Liquid desiccants are often undesirable however, because
the wet surfaces tend to collect dust and fine particulate matter
and the desiccant coating can be washed away during routine cleaning
of the wheel. Also, under certain adverse operating conditions liquid
desiccants can drip off the wheel.
To avoid these problems as encountered with liquid type desiccant
materials, it has been suggested that a Kraft or other fibous paper
may be coated with a dry desiccant material by first coating the
paper with a resinous film and then applying the desiccant particles
to the uncured resinous film, allowing them to imbed partially into
the resin. Finally, the resin is cured to provide a permanent bonding
of the desiccant particles to the treated paper surface. (See, for
example, U.S. Pat. No. 3664095.) With this type of construction,
a large fraction of the desiccant particle surface area is not able
to absorb or adsorb moisture because it is imbedded in the relatively
thick resinous coating.
Prior art enthalpy exchangers have tended to avoid the use of plastic
(i.e., high molecular weight, synthetic polymers) as the medium
comprising the heat exchange matrix because of difficulty in attaching
the desiccant in a manner providing the desired latent heat exchange
efficiency, although plastic, on the other hand, is considered a
desirable medium for a heat exchange matrix because of its low cost,
its high sensible heat transfer efficiency when configured in a
compact regenerator design, its resistance to biological degradation,
its high strength to weight ratio, and, because of its non-moisture
adsorption characteristic, its safety from a human health standpoint.
One of the principal objects of this invention is to provide a
relatively inexpensive heat exchange device for transfer of both
sensible and latent heat at relatively high efficiency from air
streams in heating, cooling or ventilating systems.
Other objects of the present invention are to provide a desiccant
heat device having the desired heat and moisture transfer effectiveness;
and to provide such a desiccant heat wheel in which the heat transfer
medium is a plastic strip, thereby achieving the attendant aforementioned
benefits of plastics (compactness, low cost, and freedom from potential
adverse health effects).
Yet further objects of this invention are to provide a method of
affixing a dry desiccant coating to a plastic strip without the
addition of a third element, such as a thickness-adding adhesive
or coating; and more particularly to provide a method of coating
a polystyrene or other plastic strip with a dry desiccant so that
only a relatively small portion of the surface area of each discrete
desiccant particle is rendered ineffective by the bond to the plastic.
Still a further object of this invention is to provide an apparatus
for efficiently bonding a dry desiccant coating to a plastic surface.
And another object of the present invention is to provide an method
of wetting dry desiccant particles with a liquid useful as a solvent
for applying the particles to a plastic surface.
Other objects of the present invention will in part be obvious
and will in part appear hereinafter. The invention, accordingly,
comprises the product possessing the features, properties and relation
of components, the process including the several steps and the relation
of one or more of such steps with respect to each of the others,
and the apparatus possessing the construction, combination of elements
and arrangement of parts, all of which are exemplified in the following
detailed disclosure and the scope of the application of which will
be indicated in the claims.
For a fuller understanding of the nature and objects of the present
invention, reference should be had to the following detailed description
taken in connection with the accompanying drawings, wherein;
FIG. 1 is a plan view, partially cut-away, of a rotary regenerative
heat wheel of the type described in U.S. Pat. No. 4432409 modified
in accordance with the present invention, herein described.
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG.
1 of the wound layers of the matrix of the wheel shown in FIG. 1;
FIG. 3 is a chart containing graphs of the relative moisture adsorbing
capacity of various dry desiccants;
FIG. 4 is a front elevation view of the apparatus of the invention
used for applying desiccant to a strip of plastic; and
FIG. 5 is a plan view of the apparatus.
The rotary regenerative heat wheel 20 shown in FIG. 1 is identical
to the wheel shown in U.S. Pat. No. 4432409 except that it has
been modified in accordance with the present invention, so as to
provide an enthalpy exchanger type heat transfer wheel. Specifically,
wheel 20 includes hub 22 about which is wound one or more thin plastic
strips 24 of sheet material, forming the medium of a heat exchange
matrix. Preferably, a pair of strips 24a and 24b are provided, with
one of the strips 24a being formed with dimples or protrusions 32
and the other strip 24b being flat. A plurality of radial spokes
25 are secured at one of their ends to hub 22 at the other of their
ends to outer casing or air seal 28 and along their length to strips
The method of making the rotary regenerative heat wheel as thus
far described is known, as illustrated in the aforementioned U.S.
Pat. No. 4432409. Briefly, however, strips 24a and 24b of selected
plastic are first wound together about hub 22 so that the strips
24a and 24b form alternate layers, as described in U.S. patent application
Ser. No. 320305 filed Nov. 12 1981 and abandoned in favor of
U.S. continuation application, Ser. No. 714685 filed Mar. 21
1985. Radial spokes 25 are then affixed to wheel 20 to provide needed
lateral stability. The spokes can be oriented along the radial lines
of the wheel, or alternatively at an angle to the radial lines as
shown in U.S. Pat. No. 4432409. As shown in FIG. 2 the dimples
32 extend in both directions from the plastic strip 24a for separating
the strip 24a from the adjacent courses of the flat strip 24b when
the strips are spirally wound onto the hub 22 so as to form air
channels 34 for the flow of incoming and outgoing air through the
wheel. Strips 24 can be made of a variety of synthetic polymers,
such as polystyrene, vinyl, polyester, or the like, with biaxially-oriented
polystyrene being preferred principally because of its heat sealing
characteristics and its relatively low cost.
According to the present invention, each strip 24 is coated, preferably
on both surfaces with dessicant 26 (one layer of which is shown
in greatly enlarged detail in FIG. 2). Several dry desiccants may
be used in coat 26 in the heat wheel in the present invention, with
silica gel and alumina gel being examples. As illustrated in FIG.
3 dried silica gel and dried alumina gel have, as compared to molecular
sieves and activated carbon, superior moisture adsorption per unit
weight over the relative humidity range of atmospheric air typically
encountered during the air conditioning season. It is believed that
the adsorptive capacity of the porous desiccants is primarily a
function of the surface area of the desiccant. Silica gel is thus
preferred, in part, over alumina gel because of the former's large
surface area per unit of mass (800 square meters per gram for silica
gel as compared to 300 square meters per gram for alumina gel).
Silica gel also has a slightly greater adsorptive capacity as compared
to alumina gel, and silica gel is readily available at a reasonable
cost. Other desiccants that could be advantageously employed include
various molecular sieves.
It is desirable to coat the gel onto the heat exchange matrix as
a very thin layer on both sides of the plastic strip 24 to maximize
the moisture-adsorbing kinetics of the desiccant. In this configuration,
water molecules carried in the air flowing through the narrow channels
34 formed between layers of the strip 24 are always in close contact
with the layer of desiccant 26. This close contact minimizes the
diffusion path length, thereby encouraging the rapid adsorption
of water vapor. Good results relating to the moisture exchange capability
of the heat wheel are achieved where silica gel particles of average
diameter of about 10 to 30 microns are applied to plastic strips
approximately three quarters of an inch (0.75 inch) wide so as to
provide a coating of silica gel having an average thickness in the
range of about 10 to about 30 microns, although it will be evident
that the dimensions can vary to suit the heat exchange matrix dimensions.
The desiccant is affixed by treating the surface of the plastic
with a selected liquid solvent so as to dissolve the plastic surface
to a minor depth so that the particles of silica gel can be applied
and become bonded to the surface. The solvent, while partially dissolving
the surface of the plastic to a minor depth, preferably is otherwise
chemically non-reactive with the plastic. Two solvents found particularly
suitable for dissolving the surface of polystyrene, while remaining
otherwise chemically non-reactive, are chloroform and tetrahydrofuran
(THF). Other solvents may be equally suitable. Of course, different
plastic strip materials will require the use of other suitable solvents.
"Liquid solvent" as used herein includes liquids with
or without a solid suspending phase.
Several methods can be used for attaching particles of desiccant
to solvent-treated plastic. In one method, the solvent treated surface
is dusted with particles of desiccant. In another method, a slurry
of desiccant and a carrier, preferably the solvent, is formed. The
strip is then dipped in the slurry or the slurry is sprayed onto
In the present invention, the preferred method of applying the
desiccant, however, includes the step of drawing the strip through
a damp mixture of powdered desiccant and solvent. The term "damp
mixture of powdered desiccant and solvent", as used above,
can be described as a mixture having just enough solvent to cause
the surfaces of the desiccant to be wet, but not enough solvent
to fill completely the interstitial volume between particles of
the desiccant. This damp powder has a consistency similar to that
of damp sand. For a silica gel/THF mixture, approximately one part
by volume of solvent is mixed with three parts of desiccant to form
the damp powder. The proportion of solvent to desiccant is critical
to the coating method of the invention. An insufficient quantity
of solvent produces poor bonding and an excessive quantity of solvent
produces distortion of the plastic strip.
Because of the difficulty of mixing a desiccant "powder"
and a liquid, such as the solvent, to obtain even coating of the
desiccant particles without the particles lumping together, as is
the case when the interstices between the particles are filled with
solvent, in accordance with one aspect of the present invention,
solvent and desiccant are place together in a predetermined proportions
and then placed in a sealed container. It was discovered that if
the solvent and desiccant are mixed in the correct predetermined
proportions, (e.g. for silica gel and THF, wherein one part solvent
by volume is added to three parts desiccant) in a sealed container,
and the container agitated for a predetermined time (typically from
one to four minutes) so as to accelerate heat and pressure build
up within the container. Then the sealed container is allowed to
cool, and then is opened, all of the desiccant powder will be substantially
evenly wetted (i.e., coated) with the solvent and the desiccant
mixture ready for use. It is believed, although not proven, that
when the container is sealed and the contents agitated, the heat
of adsorption released by the solvent as the solvent is rapidly
adsorbed by the desiccant powder causes at least a portion of the
solvent to evaporate into a vapor phase throughout the container,
which in turn further raises the temperature within the container
This in turn causes the pressure to rapidly rise to about 10 psi,
where substantially all of the liquid solvent is vaporized. In this
regard, therefore, it is believed that the same results might be
achieved if the liquid solvent and particles are mixed in their
predetermined proportions, and heated within the sealed container
with an external heater so as to raise the temperature and pressure
to the desired levels (a pressure of about 10 psi) to allow substantially
all of the liquid in the container to vaporize and distribute evenly
thoughout the particles. In either case, whether heat is provided
internally by heat of adsorption, or externally by a separate source
of heating, when allowed to cool the solvent condenses to its liquid
phase and is substantially evenly distributed throughout the desiccant
so as to substantially evenly coat the desiccant particles without
loss of solvent to the atmosphere. Alternatively, the mixture can
be mechanically mixed in an open container for an extended period
of time to achieve a similar desiccant/solvent distribution, in
which case solvent is lost to the atmosphere.
Apparatus for applying a desiccant coating to a single strip 120
of plastic, shown in FIGS. 4 and 5 includes a supply 100 of plastic
strip, preferably in the form of a dispensing wheel and a take up
drive 110 upon which the finished strip (strip 24 with desiccant
26) is wound. The apparatus also includes a frame 122 for supporting
the hollow container or tube 124 (containing the desiccant/solvent
mixture 126) for oscillatory rotation about its axis 125 of elongation,
and hollow evaporating tube chamber 128 for supplying drying air
to both sides of the strip 120 for evaporating solvent from mixture
126 applied to the strip. Although one strip 24 is shown as passing
through the apparatus of FIGS. 4 and 5 more than one strip can
be processed though the apparatus at one time, as described in greater
Preferably, tube 124 is constructed of a clear material to permit
observation of the coating process. Tube 124 has removable ends
130 and 132 for supplying mixture 126. Slits or apertures 134 and
136 are formed in ends 130 and 132 respectively, on the axis 125
for passing strip 120 into and out of tube 124 along its axis 125.
The slits are sized to retain mixture 126 inside of tube 124 while
permitting free movement of strip 120 through the slits.
A plurality of wheels 138 for rotatably supporting tube 124 are
rotatably mounted at various locations on frame 122. Tube 124 rests
on top of portions of wheels 138 and is biased downwardly against
wheels 138 by wheel 139. The tube 124 is rotatably driven alternately
in one direction then the other about its axis 125 by drive wheel
138A and by drive wheel 138B. This alternating rotation of tube
124 continually agitates mixture 126 to distribute the solvent throughout
the mixture and prevent "channeling", a condition which
would otherwise arise when, after removing a quantity of damp mixture
of powder and solvent, an empty passageway forms within the mixture
surrounding the strip because the caking tendency of the mixture
discourages adjacent mixture from filling in the passageway. Also,
continuous mixing is required since the solvent is usually depleted
faster than the desiccant so that in the absence of such mixing,
as the strip moved through the solvent desiccant mixture, the mixture
adjacent to the strip would become too dry to properly adhere to
the plastic. A constant mixing action also provides for even distribution
of solvent that may be added during the coating process to "
make-up" for the more rapid depletion of solvent.
Means are provided for counter rotating drive wheels 138A and 138B,
preferably in the form of an electric motor 140 and counterweight
142. Crank arm 144 is affixed to and driven by the output shaft
of motor 140. Line 146 is affixed to wheel 138A, and when arm 144
is in the (12 o'clock) position shown in FIG. 4 line 146 is wound
about wheel 138A. When motor 140 rotates arm 144 toward the position
diametrically opposed from that shown in FIG. 4 (the 12 o'clock
position being shown), line 146 is unwound from wheel 138A, causing
wheel 138A to rotate in one direction. Rotatably driven wheel 138A
rotatably drives tube 124 by frictional engagement. As driven wheel
138A rotatably drives tube 124 tube 124 rotatably drives frictionally
engaged wheel 138B. When wheel 138B is driven in this manner, line
148 affixed at one end to counterweight 142 and at the other end
to wheel 138B, is wound about wheel 138B. The relative driving/driven
relationships are reversed as the arm 144 continues its rotational
travel from the diametrically opposed position back toward the position
shown in FIG. 4. Specifically, counterweight 142 causes line 148
to unwind from wheel 138B thereby rotatably driving wheel 138B in
the opposite direction. Wheel 138B rotatably drives tube 124 in
the same opposite direction. Tube 124 rotatably drives wheel 138A
also in the same opposite direction causing line 146 to rewind about
wheel 138A. When arm 144 returns to the position shown in FIG. 4
one rotation cycle is completed. This alternation of driving and
driven functions between wheels 138A and 138B produces an alternating
clockwise/counterclockwise rotation of tube 124 about its axis 125.
Such alternating rotation is necessary to prevent twisting of strip
120 as it is pulled from the supply 100 through tube 124 by the
take up drive 110 as would occur if tube 124 were rotated in just
one direction. While the drive means described above is the preferred
means for rotating tube 124 other means can be advantageously used.
For instance, a collar having a V-groove formed in the peripheral
surface thereof could be affixed to tube 124. A reversible electric
motor could then drive the collar through a drive belt mounted on
the motor's output shaft.
Stop means are provided to limit the arc through which tube 124
rotates to a preselected number of degrees (typically to 360 degrees).
The stop means comprises collar 150 affixed to tube 124 to rotate
therewith, finger 152 affixed to collar 150 and stop 154 affixed
to support 156 attached to frame 122. Finger 152 is positioned on
collar 150 so that when arm 144 is adjacent the twelve o'clock position,
as shown in FIG. 4 finger 152 contacts one side of stop 154. When
arm 144 is adjacent the six o'clock position, finger 152 contacts
the opposite side of stop 154. The size and position of finger 152
and stop 154 are selected to limit the rotational arc to a chosen
number of degrees.
Wiper means 158 is provided for removing excess mixture from strip
120. Means 158 is positioned adjacent end 132 so that removed mixture
126 can fall back into tube 124 for reapplication. Plastic, cloth,
or other suitable materials, not affected by the solvent, can be
used for the manufacture of means 158.
Evaporation tube chamber 128 includes a box 160 and tube 162 for
drawing dry air through tube 128 to the box 160. Tube 128 is connected
to box 160 so that air is supplied to both sides of the strip 120
as it passes through the tube 128. Tube 128 is attached to rotate
with tube 124 in a suitable manner to prevent stretching of the
edges of the softened plastic strip as it emerges from the alternately
rotating slit 136. Suitable means, not shown, are provided in box
160 to permit tube 128 to rotate relative to the box. Tube 128 has
open ends with a frame supported slit, not shown.
The tube 124 is preferably supported at an angle by support 16,
adapted to support the frame 122 at a selected location. The angle
of inclination of tube 124 can be varied by moving support 162 so
as to contact frame 122 at various locations. Since tube 124 is
generally not completely filled with mixture 126 moving support
160 toward dispensing wheel 100 causes mixture 126 to accumulate
at end 130 thereby decreasing the length of strip 120 exposed to
mixture 126 at any one instance. Moving support 162 away from dispensing
wheel 100 causes some of the mixture 126 to move toward end 132
thereby increasing the length of strip 122 exposed to mixture 126
at any one instance. It should be appreciated that exposure time
of the strip to the solvent desiccant mixture can also be controlled
by varying the speed of the take up wheel 110.
In operation, the tube 124 is charged with a damp powder desiccant/solvent
mixture 126. The strip 120 is initially taken from dispensing wheel
100 through slits 134 into the container or tube 124 where it contacts
the "damp powder", past means 158 out of the tube through
slit 136 through the evaporation tube 128 through the frame supported
slit of tube 128 to a take up wheel 110. During this process, the
desiccant acts as a carrier of the solvent for dissolving the surface
of the plastic to a minor depth and for carrying the particles into
contact with the surface. Motor 140 is energized for alternately
rotating tube 124 about its axis 125 so as to continuously agitate
the mixture in the tube. The take up wheel 110 is driven by a motor
(not shown) to pull strip 120 through the tube, while the tube is
alternately rotated about its axis 125. The strip is preferably
pulled at a rate of approximately one foot per second with the contact
time between mixture and strip of approximately one to three seconds
producing the desired desiccant bonding. This contact time is critical
for proper application of the desiccant coating, since insufficient
contact time will result in poor bonding, while excessive contact
time causes loss of mechanical strength of the plastic with resulting
distortion of the strip. The dried coating on the strip is such
that only a small portion of the surface area of each discrete desiccant
particle is rendered ineffective by its bond to the plastic strip.
This bonding maximizes the surface area of the desiccant available
for water vapor adsorption.
When coating two are more strips, such as the strips 24a and 24b
of FIG. 2 both strips can be simultaneously pulled through the
apparatus and wound onto take-up reel 110. In such an operation,
the strips 24a and 24b are dispensed from separate dispensing wheels
100 into container 124. Preferably, each strip 24 enters through
a separate slit, similar to slit 134 so that the strips lie in
the same or parallel planes and are spaced from one another as they
enter the container 124. The strips pass through the container in
a spaced apart relation so that both sides of each strip will be
adequately coated with the mixture in the container. The coated
strips preferably pass through separate spaced apart wiper means,
similar to means 158 and out the tube through separate slits similar
to slit 136. Both strips are dried in evaporation tube 128 and preferably
passed through the frame supported slit of box 160 with one strip
on top of and in contact with the other so that they are wound together
by the take up wheel 110.
In practice, the solvent tends to evaporate from the mixture before
the desiccant is depleted from the tube 124. When the percentage
of solvent by volume drops below approximately 15%, additional solvent
must be added. The time at which additional solvent should be added
can be determined by observing the mixture through the clear tube
124. As the solvent by volume drops below about 15%, the desiccant
starts to become dry and powdery. The used mixture can be "rewetted"
with solvent using the aforementioned sealed container process.
The quantity of solvent added in this "rewetting" procedure
is chosen to bring the mixture back to its original one part solvent/three
part desiccant proportion. Alternatively, solvent may be slowly
added, for example, through the end caps of tube 124 during the
coating process to replace lost solvent.
The sensible and latent heat efficiencies of the desiccant heat
devices made according to this method are approximately equal. For
one particular rotary heat wheel design which has been tested extensively,
the sensible heat and moisture exchange efficiencies are both about
75%. Thus, the total heat content or enthalpy effectiveness of that
particular wheel is about 75%. When installed in the ventilation
system of an air conditioned structure, the reduction in the ventilating
air cooling load on a typical warm humid day (95 degrees F. outdoor
air temperature, and 73 degrees F. dew point) is about 25% due to
transfer of sensible heat and about 50% due to transfer of latent
heat (moisture) for a total of about 75% reduction in ventilating
air cooling load. Thus, the presence of the desiccant for moisture
transfer is very important to the overall energy savings under these
It should be appreciated that the method of the present invention
and the apparatus for carrying out the method can be utilized to
make other product besides the desiccant rotary heat wheel described.
For example, the method can be used to make plastic stationary periodic
flow regenerators. The plastic material can be in any form, such
as sheet form, in a honeycomb structure, in block form, etc. Further,
plastic sheets and similar materials for use in chromatography can
be coated on one or both sides with a desiccant material. Where
it is desirable to coat only one side of a plastic sheet or strip
material, one side of the sheet or strip has affixed thereto a layer
of material that does not chemically react with the selected solvent/powder
mixture. As the plastic material is drawn through the mixture, the
desiccant mixture will not adhere to the non-reactive layer.
It also should be appreciated that in addition to controlling the
angle of tube 128 so as to control the amount of mixture to which
the strip is in contact so as to control the time of exposure, the
time the plastic is exposed to the solvent before the solvent evaporates
in the evaporation tube 128 can also be controlled chemically. For
example, a non-reactant dilutant, such as alcohol, can be added
to the solvent prior to mixing the solvent with the desiccant in
a sealed container. The amount of dilutant added is a function of
the solvent reaction time desired. The greater the amount of dilutant
by volume added to the solvent the slower the reaction time of the
solvent on the plastic material.
Since certain changes may be made in the above processes without
departing from the scope of the invention hereininvolved, it is
intended that all matter contained in the above description or shown
in the accompanying drawings shall be interpreted in an illustrative
and not in a limiting sense.