U.S. patent application number 11/739580 was filed with the patent office on 2007-11-08 for water extraction from air and desalination.
Invention is credited to Melvin L. Prueitt.
Application Number | 20070256430 11/739580 |
Document ID | / |
Family ID | 38659979 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070256430 |
Kind Code |
A1 |
Prueitt; Melvin L. |
November 8, 2007 |
WATER EXTRACTION FROM AIR AND DESALINATION
Abstract
This invention is a water producer that extracts water from the
air. One embodiment of the invention adiabatically compresses and
heats the air. The heated air is cooled through a counter-flow heat
exchanger so that it becomes supersaturated and water condenses.
The air is then cooled further and passed back through the heat
exchanger to recover its former heat. It then passes through an
adiabatic expander to recover energy. A second embodiment utilizes
a unique isothermal compressor/expander to compress the humid air
isothermally so that the air becomes supersaturated with water, and
the water condenses. The air is then cooled to remove the heat of
condensation of the water and returned to the isothermal
compressor/expander to recover energy. A third embodiment draws in
humid air through a counter-flow heat exchanger to cool it down
below its dew point so that water is collected. The air is then
cooled adiabatically and passed back through the counter-flow heat
exchanger and on to a compressor, which compresses the air back to
ambient pressure and pushes the air out. These embodiments can be
used to desalinate seawater, brackish water, or desiccant aqueous
solutions by having a humidifier evaporate water from the liquids
to make the input air to the water producer very humid.
Inventors: |
Prueitt; Melvin L.; (Los
Alamos, NM) |
Correspondence
Address: |
Melvin Prueitt
161 Cascabel St.
Los Alamos
NM
87544
US
|
Family ID: |
38659979 |
Appl. No.: |
11/739580 |
Filed: |
April 24, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60746271 |
May 3, 2006 |
|
|
|
Current U.S.
Class: |
62/93 ; 62/285;
62/331 |
Current CPC
Class: |
B01D 5/006 20130101;
C02F 1/048 20130101; Y02P 70/10 20151101; Y02P 70/34 20151101; Y02A
20/128 20180101; B01D 53/265 20130101; Y02A 20/124 20180101 |
Class at
Publication: |
62/93 ; 62/285;
62/331 |
International
Class: |
F25D 17/06 20060101
F25D017/06; F25D 21/14 20060101 F25D021/14; F25D 23/12 20060101
F25D023/12 |
Claims
1. A water and power producing system comprising: an adiabatic
compressor for compressing and thus increasing the temperature of
humid air; and a counter-flow heat exchanger to cool the compressed
humid air; and a condenser to condense water from the compressed
and cooled humid air; and a cooler to further cool the humid air
and condense more water and to provide cooling to the cool end of
the counter-flow heat exchanger; and a pipe to conduct the cool air
back to the cool end of counter-flow heat exchanger; and a heater
to heat the air further after the air leaves the counter-flow heat
exchanger, which heater may receive heat from solar energy or other
energy source; and an adiabatic expander for expanding the air
after it has flowed back through the counter-flow heat exchanger
and become re-heated; a drain to drain condensed water; and valves
to control the flow of air; wherein the adiabatic compressor draws
in ambient air, compresses it, and forces it into the counter-flow
heat exchanger, where the air cools and becomes super-saturated
with water vapor, some of the water vapor condenses in the
condenser and flows out the drain, the air flows to the cooler,
where it is cooled further and more water is condensed and flows
out the drain, the air flows back through the counter-flow heat
exchanger to be heated as it cools the air that flows the opposite
direction, the re-heated air flows through the heater to be further
heated and flows into an adiabatic expander that extracts
mechanical energy from the air as the air expands, which mechanical
energy may be used to drive an electric generator, and the
adiabatic expander pushes the air into the atmosphere.
2. A water and power producing system according to claim 1, wherein
the cooler is an adiabatic expander cooler that extracts additional
energy from the air as it cools the air and condenses water, which
is drained through the drain.
3. A water and power producing system according to claim 1, wherein
the adiabatic compressors and adiabatic expanders are reciprocating
piston-in-cylinder type compressors and expanders.
4. A water and power producing system according to claim 1, wherein
the adiabatic compressors and adiabatic expanders are rotating
piston type compressors and expanders.
5. A water and power producing system according to claim 1, wherein
the adiabatic compressors and adiabatic expanders are turbine type
compressors and expanders.
6. A water and power producing system according to claim 1, wherein
the adiabatic compressors and adiabatic expanders are bellows type
compressors and expanders.
7. A water producing system comprising: an isothermal
compressor/expander for compressing humid air and thus increasing
the relative humidity of the air, and for expanding the air after
some water has been removed from the air; and a condenser to
condense water from the compressed air; and a cooler to further
cool the humid air and condense more water and to provide cooling
to remove the latent heat of condensation of the water and to keep
the isothermal compressor/expander cool; and a pipe to conduct the
cool air back to the isothermal compressor/expander; and a drain to
drain condensed water; and valves to control the flow of air;
wherein the isothermal compressor/expander draws in ambient air,
compresses it, and forces it into the condenser, where some of the
water vapor condenses in the condenser and flows out the drain, the
air flows to the cooler, where it is cooled further and more water
is condensed and flows out the drain, the air flows back into the
isothermal compressor/expander that extracts mechanical energy from
the air as the air expands, and the isothermal compressor/expander
pushes the air into the atmosphere.
8. A water producing system according to claim 7, wherein the
isothermal compressor/expander consists of: a piston contained in a
cylinder; and closely spaced tapered plates or tapered concentric
circular forms attached to the face of the piston for the purpose
of receiving heat from compressing air and supplying heat to
expanding air to keep the air close to isothermal; and closely
spaced tapered plates or tapered concentric circular forms attached
to the bottom of the cylinder for the purpose of receiving heat
from compressing air and supplying heat to expanding air to keep
the air close to isothermal; wherein the closely spaced tapered
plates or tapered concentric circular forms attached to the face of
the piston fit between the closely spaced plates attached to the
bottom of the cylinder when the piston approaches the bottom of the
cylinder.
9. A water producing system according to claim 7, wherein the
isothermal compressor/expander consists of: two rotating pistons
within a housing, which rotating pistons roll together to form a
seal; and closely spaced tapered plates or tapered concentric
circular forms attached to the inside of the rotating pistons for
the purpose of receiving heat from compressing air and supplying
heat to expanding air to keep the air close to isothermal; and
closely spaced tapered plates or tapered concentric circular forms
attached to the housing for the purpose of receiving heat from
compressing air and supplying heat to expanding air to keep the air
close to isothermal; wherein the closely spaced tapered plates or
tapered concentric circular forms attached to first side of the
rotating pistons fit between the closely spaced tapered plates or
tapered concentric circular forms attached to the first side of the
housing when the rotating piston rotate toward the first side of
the housing, and wherein the closely spaced tapered plates or
tapered concentric circular forms attached to the second side of
the rotating pistons fit between the closely spaced plates or
tapered concentric circular forms attached to the second side of
the housing when the rotating piston rotate toward the second side
of the housing.
10. A water producing system according to claim 7, wherein the
isothermal compressor/expander consists of: a bellows
compressor/expander; and closely spaced tapered plates or tapered
concentric circular forms attached to the inside top of the bellows
for the purpose of receiving heat from compressing air and
supplying heat to expanding air to keep the air close to
isothermal; and closely spaced tapered plates or tapered concentric
circular forms attached to the bottom of the bellows for the
purpose of receiving heat from compressing air and supplying heat
to expanding air to keep the air close to isothermal; wherein the
closely spaced tapered plates or tapered concentric circular forms
attached to the top of the bellows fit between the closely spaced
plates or tapered concentric circular forms attached to the bottom
of the bellows when the top of the bellows approaches the bottom of
the bellows.
11. A water producing system according to claim 7, wherein the
cooler is an adiabatic expander cooler that extracts additional
energy from the air as it cools the air and condenses water, which
is drained through the drain.
12. A water and power producing system according to claim 1,
wherein a humidifier provides high humidity to the air that is
drawn into the water and power producing system, which humidifier
has a plurality of slanted sheets on which a film of seawater,
brackish water, or desiccant aqueous solutions flow while the air
flows over the film of liquid to absorb the water vapor from the
liquid.
13. A water producing system according to claim 7, wherein a
humidifier provides high humidity to the air that is drawn into the
water producing system, which humidifier has a plurality of slanted
sheets on which a film of seawater, brackish water, or desiccant
aqueous solutions flow while the air flows over the film of liquid
to absorb the water vapor from the liquid.
14. A water and power producing system according to claim 1,
wherein a humidifier provides high humidity to the air that is
drawn into the water producing system, which humidifier has an
upper and lower chamber with a slanted sheet separating the two
chambers on which sheet a film of seawater, brackish water, or
desiccant aqueous solutions flow while the air flows over the film
of liquid to absorb the water vapor from the liquid, and wherein
heat is supplied from the lower chamber to help evaporate the
water, which heat is provided by air flowing from the condenser of
the water producing system, and which air flows out of the lower
chamber after having been cooled back to the counter-flow heat
exchanger.
15. A water producing system according to claim 7, wherein a
humidifier provides high humidity to the air that is drawn into the
water producing system, which humidifier has an upper and lower
chamber with a slanted sheet separating the two chambers on which
sheet a film of seawater, brackish water, or desiccant aqueous
solutions flow while the air flows over the film of liquid to
absorb the water vapor from the liquid, and wherein heat is
supplied from the lower chamber to help evaporate the water, which
heat is provided by air flowing from the condenser of the water
producing system, and which air flows out of the lower chamber
after having been cooled back to the isothermal
compressor/expander.
16. A water producing system comprising: a counter-flow heat
exchanger to cool inflowing humid air; and a condenser to condense
water from the cooled humid air; and a an adiabatic expander cooler
to further cool the air and condense more water and to provide
cooling to the cool end of the counter-flow heat exchanger; and a
pipe to conduct the cool air from the adiabatic expander cooler
back to the cool end of counter-flow heat exchanger; and an
adiabatic compressor for compressing the air after it flows back
through the counter-flow heat exchanger and becomes re-heated; a
drain to drain condensed water; wherein the adiabatic expander
cooler draws in ambient air through the counter-flow heat
exchanger, which cools the air, and draws the air through the
condenser where water condenses and flows out the drain, and the
adiabatic expander cooler expands the air, further cooling it and
condensing more water, which water flows out the drain, and the
adiabatic expander cooler forces the air through the pipe back into
the counter-flow heat exchanger to be heated as it cools the air
that flows the opposite direction, the re-heated air flows into an
adiabatic compressor that compresses the air and pushes the air
into the atmosphere.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This claims priority to and the benefit of Provisional U.S.
Patent Application Serial No. 60/746,271, filed May 3, 2006, the
entirety of which is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The earth's atmosphere carries an enormous amount of water.
At 50% relative humidity, the amount of water flowing in a 10 mile
per hour wind over a farmer's square-mile farm in Kansas with a
clear sky overhead amounts to 6.9 billion gallons per day. That is
21,140 acre-feet, enough to cover the farmer's land to a depth of
33 feet of water every day. The winds over the U.S. carry far more
water than all the American rivers combined. Most of that water is
carried back out over the oceans without being used.
[0003] There are many places in the world that have a severe
shortage of water, but machinery could be built to supply water
from the air. Most water extraction mechanisms require a lot of
energy. Some of them use refrigeration that cools a surface to
cause water condensation. A typical refrigeration device that
removes water from the air requires about 2 kWh (depending on the
humidity) to produce a gallon of water. If the electricity costs 9
cents per kWh, the cost is 18 cents per gallon or $180 per thousand
gallons. Current seawater desalination plants can produce fresh
water for $2 to $6 per thousand gallons. (But 18 cents per gallon
is cheap compared to bottled water prices).
[0004] It is well known that compression of air can increase the
relative humidity of the air. If the air is compressed
sufficiently, the relative humidity can exceed 100%, which means
that it will condense on surfaces. One problem is that when air is
compressed adiabatically, it gets hot, and that lowers the relative
humidity. U.S. Pat. No. 6,360,549, Spletzer, et al, from the Sandia
National Laboratories describes a device that incorporates a piston
in a cylinder to compress air into a porous medium where the water
can condense. The claim is that it is near isothermal (constant
temperature) operation, which means that it does not get hot. The
problem with this design is that the air that is being compressed
gets hot before it reaches the porous medium. It cools inside the
medium so that condensation can occur. Then, when the piston moves
the other direction, the air that comes out of the medium expands
and cools almost adiabatically unless the piston is moving slowly.
This means that the expansion of the air returns less of the energy
that was put into it. These problems can be overcome by operating
the engine very slowly so that the air can cool against the piston
and cylinder walls during compression and receive heat during
expansion. But this would mean that the device would be very slow
and would take a long time to produce a gallon of water.
[0005] The patent from the Sandia National Laboratories states that
it is theoretically possible to get excess energy from their
system. That is, since the condensing water releases heat, the
machine becomes a heat engine that not only produces water but also
produces energy. That will not work with their system, because if
their system is isothermal, any extra heat produced by water
condensation would be absorbed by the same mechanism that keeps the
air isothermal. If their system were adiabatic, the mechanical
parts would heat up until water would no longer condense.
[0006] Parenthetically, it should be noted that one of the problems
with the Spletzer patent discussed above is that the water is
deposited in a porous material at the end of the cylinder in which
the piston is located. When the piston finishes compressing the air
into the material, the piston withdraws, and the air pressure
drops. At that point, the water would start evaporating from the
porous material just as fast as it condensed. In the patent, it
explains that the water would not evaporate, because it is drained
out of the material. If the machine has to wait until the water is
drained, it will be a very slowly operating device. Furthermore,
and water clinging to the inside of the pores of the material will
evaporate.
[0007] Other US patents that are somewhat related to embodiments of
the present invention are U.S. Pat. Nos. 4,676,067, 5,641,273, and
6,511,525.
SUMMARY OF THE INVENTION
[0008] A device that we may call the "Water Producer" overcomes the
problems outlined above. The air is removed from the compression
device before condensation occurs. It is theoretically possible to
use very little energy to separate the water from the air. Most of
the energy requirements are used to overcome friction and
aerodynamic losses. Since large quantities of air must be handled,
these friction losses must be reduced as much as possible. There
are some methods to reduce the mechanical losses considerably, and
some of these are considered later in this document. We also need
to use highly efficient counter-flow heat exchangers.
[0009] An added advantage to one of the devices described below is
that if solar energy is available, the solar heat can be introduced
at a specific point in the cycle, and it can generate electric
power, and the use of the solar energy is very efficient. This
eliminates the problem of having to set up a separate engine to
drive the Water Producer.
[0010] Note that this system can not only be placed next to the
ocean, but it can be placed in the desert, where it will need no
cooling towers to generate water and electric power. The water
output will be less, if the humidity is low. There are places in
Africa and elsewhere where the humidity is high but the rainfall is
low.
[0011] The Water Producer can be used not only as large power
plants, but small units can be built to put in people's back yards
to generate electricity and fresh water for the home and can be
placed on rooftops of businesses.
[0012] Military units can use portable Water Producers in the field
to provide water without having to haul tank loads of water.
[0013] It is therefore an object of the present invention to
efficiently extract water vapor from the air and condense the vapor
to liquid water using an adiabatic compression and expansion
machine.
[0014] It is another object of the present invention to efficiently
extract water vapor from the air and condense the vapor to liquid
water using an isothermal compression and expansion machine.
[0015] It is another object of the present invention to provide
methods of humidifying intake air to the Water Producer by flowing
air over seawater, brackish water, or desiccant aqueous
solutions.
[0016] It is another object of the present invention to utilize
solar energy or other heat sources to provide energy to run the
Water Producer and to generate electric power.
[0017] It is another object of the present invention to provide
means for reducing mechanical losses in the compression and
expansion devices.
[0018] It is another object of the present invention to provide
methods of preventing or slowing condensation of water at
inappropriate times in the machine cycles.
[0019] It is another object of the present invention to provide
methods to effectively allow approximate isothermal compression and
expansion.
[0020] It is another object of the present invention to provide
simplified Water Producer that does not involve high temperatures
or pressures.
[0021] Other objects, advantages and novel features, and further
scope of applicability of the present invention will be set forth
in part in the detailed description to follow, taken in conjunction
with the accompanying drawings, and in part will become apparent to
those skilled in the art upon examination of the following, or may
be learned by practice of the invention. The objects and advantages
of the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0022] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate embodiments of the
present invention and, together with the description, serve to
explain the principles of the invention. The drawings are only for
the purpose of illustrating preferred embodiments of the invention
and are not to be construed as limiting the invention. In the
drawings:
[0023] FIG. 1 is a schematic side view of the adiabatic embodiment
of the present invention showing an adiabatic compressor and an
adiabatic expander.
[0024] FIG. 2 is a schematic side view of an embodiment of the
present invention showing an isothermal compressor/expander.
[0025] FIG. 2A is a schematic isometric view tapered concentric
circular forms for increasing surface contact with gases for
isothermal compressors and expanders.
[0026] FIG. 3 is a schematic that illustrates the use of a
humidifier to humidify air that can be drawn into a Water Producer
to desalinate seawater, brackish water, or a desiccant aqueous
solution.
[0027] FIG. 4 is drawing representing one form of the cooler for
desalination systems, and at the same time, it provides humid air
for the Water Producer.
[0028] FIG. 5 is an artists conception of an inside view of a
rotating piston engine.
[0029] FIG. 6 is a schematic top view of a modified rotating piston
engine featuring tapered plates for isothermal operation.
[0030] FIG. 7 is a side view schematic of a bellows compressor
and/or expander.
[0031] FIG. 8 is a schematic side view drawing of a low friction
bellows compressor utilizing a hinge on one side.
[0032] FIG. 9 is a schematic side view of an embodiment of the
present invention that provides a simplified method of extracting
water from the air efficiently.
DETAILED DESCRIPTION OF THE INVENTION
Adiabatic Water Producer
[0033] We can use isothermal compression or adiabatic compression
to provide the increased pressure of the air. We first consider the
adiabatic method. In this case, we would prefer to minimize the
heat exchange between the air and the cylinder walls and the
piston, since this represents an energy loss. The interior volume
of the cylinder should be relatively large, and the cylinder walls
and the piston face should be lined with Teflon or other insulating
material. Having the machine run fast also reduces heat loss.
[0034] FIG. 1 shows one embodiment of the adiabatic Water Producer.
For the first stroke, the piston 4 in the compressor 1 moves upward
and draws in ambient air through intake 2 with valve 3 open. Then
valve 3 closes, and the piston 4 moves downward and compresses and
heats the air. When the air pressure in the compressor 1 becomes
greater than the pressure in the counter-flow heat exchanger 6, the
check valve 5 opens and compressed air flows into the counter-flow
heat exchanger 6, which has parallel chambers with down-flowing and
up-flowing air flowing in alternate chambers. The air in the heat
exchanger 6 is continually pressurized with air.
[0035] It would be preferable to have the interior surfaces of the
heat exchanger in the down-flowing chambers coated with a
hydrophobic material, such as Teflon to prevent condensation. When
the air flows out the bottom of the heat exchanger, it flows into a
condenser 7, which is filled with fibrous hydrophilic material to
provide condensing surfaces for the water. This heats and expands
the air. The condensed water flows out a drainpipe 16.
[0036] The air flows out the bottom of the condenser and into a
cooler 8, which is shown as an adiabatic expander in FIG. 1. The
purpose of the cooler is to maintain the temperature gradient from
the top to the bottom of the counter-flow heat exchanger 6. By
using an adiabatic expander as a cooler, the energy that the
condensing water imparts to the air can be reclaimed. This energy
can be used to help drive the moving parts of the Water Producer.
Alternatively, the cooler could be cooled by ambient air blown
through cooling fins or by other means, but this does not recover
any mechanical energy. More water condenses in the cooler 8 and
flows out the drainpipe 18. The air flows into the reservoir 9 and
then flows back up through the counter-flow heat exchanger 6, where
it heats up as it receives heat from the down-flowing air. By the
time it reaches the top, it is nearly as hot as the down-flowing
air at the top.
[0037] If an external heat source, such as solar energy, is used,
that energy flows into the super heater 15. If no external source
of heat is used, the super heater is eliminated. The high-pressure
air then flows through valve 10 into the expander cylinder 11 and
returns energy to the system as it pushes piston 12 upward. Valve
10 closes, and the air continues to push the piston in an adiabatic
expansion. When the piston reaches the top, the air has returned to
near ambient conditions (minus some water). Valve 13 opens, and the
air is forced out the exhaust pipe 14. The system is ready for a
repeat performance. In fact, the compressor and expander should be
operating at the same time, 180 degrees out of phase. There could
be a number of compressors and expanders feeding the same heat
exchanger.
[0038] In the adiabatic embodiment of the Water Producer, the air
is heated by the compression, and then the air is cooled in the
heat exchanger to enhance water extraction. The heat is returned to
the air so that it can return energy to the system through
adiabatic expansion. Again, theoretically, very little energy is
used to remove water from the air.
[0039] Instead of using a piston compressor and a piston expander,
other types of compressors and expanders, such as turbines or
scroll devices could be used.
[0040] The adiabatic method requires more energy to compress the
air, but it gets more energy back during expansion. An advantage of
the adiabatic method is that water is less likely to condense in
the compressor but will readily condense in condenser and the
cooler.
Isothermal Water Producer
[0041] FIG. 2 is a schematic that illustrates a new type of
isothermal compressor and expander. In order to increase heat
transfer from the air to the metal, the surface area is greatly
increased by placing tapered plates 22 on the front of the piston
21 and tapered plates 23 on the bottom of the cylinder 20, leaving
channels for air flow. These plates could have flat surfaces as
shown in the diagram, or they could have circular concentric
configurations as shown in FIG. 2A.
[0042] In operation, valve 25 is opened and the piston 21 in the
pump cylinder 20 moves upward so that it draws in fresh air from
the outside through intake 24. When the piston reaches its maximum
height, valve 25 is closed, and the piston is forced downward,
compressing the air. As the air is compressed, it tends to increase
in heat, but the tapered plates absorb the heat of the air. Since
the heat capacity of the metal plates is about 2000 times as great
as the air (per unit volume), the plates' temperature does not rise
very much during one half cycle.
[0043] When the piston has traveled down far enough to provide the
appropriate pressure the air, valve 26 opens to allow the air and
its water vapor to flow through check valve 27 and to enter the
condensation tank 28, which has about the same pressure as the air
in the pump cylinder 20. The piston continues to move downward to
force the air into the condensation tank.
[0044] The inside pump cylinder walls and the tapered plates should
be coated with a very thin layer of Teflon or other hydrophobic
material. This prevents the water vapor from readily condensing on
the plates. Any droplets that do form would tend to be thrown
downward as the piston decelerates and to be blown out by the air
rushing into the condensation tank. The coating should be as thin
as possible so that it does not hinder heat transfer. The
condensation tank 28 is filled with hydrophilic material 29 that
could be fibrous. The water vapor in the air at this point is above
the saturation value (greater than 100% relative humidity), so it
condenses on the hydrophilic material and runs down out of the tank
for useful purposes. There could be several cylinders and pistons
that alternately feed air to the tank and take air out of the
tank.
[0045] While the pump 20 forces air into the condensation tank 28,
the adiabatic expander 32 draws in air through valve 31 from the
condensation tank. When the appropriate amount of air is drawn in,
valve 31 closes, and the air in the expander 32 is expanded
adiabatically until it reaches a specified volume. The piston
reverses direction, and valve 34 is opened so that the air is
expelled into the reservoir 35. When piston 21 moves upward, it
draws air from reservoir 35 through check valve 36 and valve 26.
The air tends to cool during expansion, but the tapered plates 22
and 23 supply heat to keep the air near isothermal. When piston 21
reaches the top, it reverses, as valve 26 closes and valve 25
opens. The air is forced out intake pipe 24.
[0046] Calculations show that the air will remain near isothermal
during both compression and expansion, since the air has close
proximity to the plates for heat transfer, and the motion of the
plates create turbulence that further enhance heat transfer.
[0047] The condensation of the water in the condensation tank
releases the latent heat of condensation, and this heats the air,
causing expansion of the air. If the condensation tank does not
have sufficient volume to accommodate the extra volume without
significantly increasing the pressure, a reservoir can be placed
adjacent to the tank.
[0048] Expansion of the air causes the system to behave as a heat
engine, since the volume of the air flowing out of the expander is
greater than the volume of air flowing out of the pump.
[0049] In the Water Producer, described in this document, the air
is forced out of the pump into the condenser, and the water
condenses in a separate chamber, where the air pressure is
maintained so that it causes condensation and prevents evaporation.
This is in contrast to the method used in the Sandia National
Laboratories' patent, which has the condensation system inside the
compressor.
[0050] In the discussion above, tapered plates are described as
providing large surfaces for heat transfer to the air. In many
applications, it may be better to use tapered concentric circular
forms that are approximately cylindrical. FIG. 2A is a schematic
drawing showing the tapered concentric circular forms 38 mounted on
a base 39. The circular forms would fit better in a cylinder such
as 20 in FIG. 2 than flat plates. The tapered plates 23 of FIG. 2
could actually be the tapered concentric circular forms 38. Similar
circular forms could be attached to piston 21 in FIG. 2.
Desalination
[0051] FIG. 3 shows humidifier 41 for providing high humidity to
the air. The air flows from the Water producer 40 through pipe 46
to a manifold 43, which distributes the air between metal plates
42. The humidifier consists of a number of flat plates 42, that can
be metal or a hydrophilic plastic. Seawater or brackish water
enters through pipe 44 and flows through a manifold 49 on the left
and is distributed to the top surfaces of the plates 42. The water
runs down the plates as a film. Air flowing between the plates
becomes humidified and is drawn through pipe 47 into the Water
Producer 40, where some of the water is removed as fresh water. The
exhaust air from the Water Producer flows back to the humidifier to
be re-humidified again. Collected fresh water flows out drain 48.
An important feature of this method is that the air will be
dust-free. If there is particulate matter in air drawn directly
from the atmosphere, water will condense on these particles before
the air reaches the condenser.
[0052] Incoming seawater can be used as the heat exchange fluid in
a cooler 8 of FIG. 1 (if an adiabatic expander is not used) to cool
the air before it returns to the heat exchanger. In FIG. 2, cool
seawater could be used to cool the air in place of the adiabatic
expander 32 is not used.
[0053] FIG. 4 shows an effective way to humidify air, and at the
same time, act as a cooler in FIGS. 1 and 2 when the Water Producer
is used as a desalination unit, in case the adiabatic expander 8 or
32 is not used. It consists of metal sheets 51 that form two
enclosed chambers 53 and 59. Seawater enters through pipe 55 and
flows as a film 56 down the floor of the upper chamber 53 and is
heated by heat from below. The seawater flows out pipe 57. Exhaust
air from the Water Producer flows in through pipe 52 over the water
film 56 and becomes humidified. It then flows back to the Water
Producer through pipe 54. Air flowing out of the condenser (7 in
FIG. 1 or 28 in FIG. 2) enters the bottom chamber 59 and deposits
heat into the seawater film in chamber 53. After being cooled, this
air flows out through pipe 60 and to the air reservoir (9 of FIG. 1
or 35 of FIG. 2). This method will transfer heat from the air in
the bottom chamber 59 and heat the water in the top chamber 53, but
it will not generate any power.
[0054] Since the exhaust air from the expander 11 of FIG. 1 is
warmer than the intake air, it can also be used to heat the
seawater.
[0055] For the devices described in FIGS. 4 and 5, instead of using
seawater or brackish water, a solution of desiccant and water can
be pumped through the water channels. The desiccant solution can
then be pumped back to a device that blows air across the surface
of the solution so that it can absorb more water from the air. It
would then flow back to the humidifier again.
More Efficient Compressors and Expanders
[0056] One of the main sources of inefficiency for a
compressor/expander engine that is needed for the Water Producer is
sliding friction of the piston. I have a U.S. Pat. No. 6,401,686)
that is often referred to as "MECH," which stands for motor,
expander, compressor, and hydraulics. Since it uses rolling
friction between two rotating pistons rather than sliding friction
of a standard piston engine, the friction losses are much less. The
rotating pistons do not touch the cylinder walls. There is sliding
friction on the ends of the pistons, but this can be relatively
small by making the pistons long compared to the diameter.
[0057] It is well known that rolling friction is only about 1/100
as large as sliding friction. A MECH prototype that we built
demonstrated only 8% as much energy loss as a comparable size
piston engine. It provides an engine with unprecedented economy for
producing water from the air or for desalinating seawater.
[0058] FIG. 5 is an artist's conception of a MECH engine 65 with
the end plate removed. One can see how the two rotating pistons 66
roll together at the contact line 67. It could be used as a
compressor and expander for the design of FIG. 1. In fact, a single
MECH engine could be compressing air in the top chambers 68 while
it is expanding air in the bottom chambers 69, and vice versa.
[0059] FIG. 6 shows a top view of a compressor/expander (it can be
used as a compressor or expander or both) that is similar to a MECH
engine in that it has two rotating surfaces that roll together. It
is designed to be an isothermal compressor and/or expander. The
MECH compressor already has one advantage over standard compressors
for isothermal compression: it has larger surface areas of the
cylinder walls and piston surfaces for absorbing heat during
compression and for returning heat during expansion. The rotating
pistons rotate almost 180 degrees in one direction and then reverse
directions for almost 180 degrees. The pistons do not touch the
cylinder walls. Sliding friction occurs only at the ends of the
pistons where they meet the end of the cylinders. The seal to
prevent air leakage is formed at the rolling contact point between
the two pistons.
[0060] FIG. 6 is a schematic top view of a modified MECH
compressor. Cylinders 75 are machined out of a block 70. Each
rotating piston 71 consists of a hollow half-cylinder that is open
on one side. The half-cylinder is connected to the shaft 77 by a
partition 74. Tapered plates 72, like those in FIG. 2 are placed
inside the half cylinder 71. The top and bottom of the rotating
piston 71 are closed with half-circle plates; they are not shown,
because they are on the near end and far end of the half-cylinder
(above and below the page). When the right piston rotates to the
right and the left piston rotates to the left, the upper tapered
plates will move into the volume where stationary tapered plates 73
are located and will fit between the stationary plates. The
stationary tapered plates are attached to the separator 79. The air
in the spaces will be compressed and squeezed out the
exhaust/intake pipes 76. At the same time, air will be drawn into
the bottom half of the engine through the other pipes 78. When it
rotates the other direction, air in the bottom half will be
compressed.
[0061] The tapered plates provide large surface areas for the
transfer of heat to and from the air. The motion of the tapered
plates relative to the stationary plates causes air turbulence in
the small gaps between them, and this enhances heat flow.
[0062] FIG. 7 shows a design that incorporates bellows 83 to
compress and expand air. The bellows is connected to the top 80 and
to a base 86. Push rod 81 moves the top up and down. The inside
surfaces can be coated with hydrophobic materials. The purpose of
the displacer 84 is to push out as much air as possible when the
bellows is compressed as far as possible. Air flows in and out of
pipe 86.
[0063] For an isothermal compressor, the tapered plates like those
of FIG. 2 can be connected to the displacer 84 and to the base
85.
[0064] One source of friction in the design of FIG. 7 is that the
push rod 81 would need to have a sliding bearing on it to keep it
aligned with the center of the bellows compressor. It would also
need a bearing on the upper end of it that connects a connecting
rod to a flywheel. The design of FIG. 8 avoids problem by having a
bellows 90 that opens like a fireplace bellows. There is a hinge 92
on the bottom. Rigid side 91 provides a place to attach a
connecting rod 94 that connects to flywheel 95. Rigid structure 93
supports the other side of the bellows. In the center of the
bottom, there is an inlet/outlet (not shown). This design has low
friction bearings at the ends of the crank rod.
Required Cooling and Heating
[0065] There may be some situations in which the tapered plates of
the embodiment of FIG. 2 need some cooling or heating. The incoming
air provides some stabilization of the temperatures. If more
cooling or heating is needed, the tapered plates can be hollow and
cooling or heating fluid can flow through them. In the case of the
compressor/expander of FIG. 6, the liquid can flow through an axial
hole in the center of the shaft 77 to cool the rotating plates 72.
The stationary plates 73 can receive liquid through the separator
79. The cylinder walls 75 can have fluid channels on the
outside.
[0066] For the desalination system, cool ocean water can provide
cooling for the compressor. Rather than flow ocean water through
the compressor plates and walls, the seawater could cool a coolant
fluid in a heat exchanger, and the coolant could flow through the
compressor. Also, since evaporating seawater gets cold, a device
like that of FIG. 4 could provide coolant by having the liquid
coolant flow through the bottom chamber 59 rather than having air
flow through. The heat supplied to the seawater would help to
evaporate the seawater and humidify the air. In this case, ambient
desert air could supply heat for the expander. Simple solar
collectors could also supply the heat.
A Simple Water Producer
[0067] FIG. 9 presents a simple method of extracting water from the
air that will reduce the required energy in comparison to present
day water producers, but it cannot produce excess energy. Humid air
is drawn into a counter-flow heat exchanger 100 at the top left
opening 101. The heat exchanger is shown as two long chambers with
a heat transfer partition 110 between them, but in a real device,
it would have many parallel chambers.
[0068] As the air flows down through the heat exchanger in chamber
102, it is cooled by releasing heat through the partition 110 to
the rising cool air on the right of the partition in chamber 106.
As the air cools at atmospheric pressure, the relative humidity
rises. At the bottom, the air flows into a condenser 103, which is
filled with hydrophilic fibers that collect the water from the
supersaturated air.
[0069] The water flows out the drainpipe 109, while the air is
drawn into an adiabatic expander 104. When the air is adiabatically
expanded, it cools further, and more water condenses. The cold air
then flows through pipe 105 to the right side of the heat exchanger
and into chamber 106, where it absorbs heat from the down-flowing
intake air. At the top, the air is drawn into the compressor 107
and is compressed adiabatically back to atmospheric pressure and
then expelled to the atmosphere through pipe 108.
[0070] A computer Fortran program, Waterair.f, calculates the
performance of this machine for various input parameters. If the
ambient temperature is 25 degrees C and the relative humidity is
90%, for each cubic meter of air processed, the device
theoretically produces 18 grams of water and requires 28 calories
(117 joules) of energy. If the humidity is 50%, it produces 10
grams of water at a cost of energy of 37 calories per gram. With
30% relative humidity, it produces 5 grams at 43 calories per
gram.
[0071] Modern water producers that use a refrigeration system to
remove water from the air require 300 to 1,000 calories per gram of
water. The present invention does not require Freon refrigerant,
with its complications, and it does not require fans to cool a
refrigerant condenser. An advantage of this design over the Water
Producers of FIGS. 1 and 2 is that it does not have high
temperatures and high pressures. But it does not produce any excess
energy.
[0072] If we can reduce the cost to a tenth (or even a fourth) that
of other machines, we should be able to help the world with its
water problems.
* * * * *