U.S. patent application number 12/245224 was filed with the patent office on 2009-10-22 for isothermal power system.
Invention is credited to Melvin L. Prueitt.
Application Number | 20090260361 12/245224 |
Document ID | / |
Family ID | 39885383 |
Filed Date | 2009-10-22 |
United States Patent
Application |
20090260361 |
Kind Code |
A1 |
Prueitt; Melvin L. |
October 22, 2009 |
ISOTHERMAL POWER SYSTEM
Abstract
This invention provides means for producing power by using
isothermal compressors and isothermal expanders. One embodiment has
an isothermal compressor that compresses air (or other gas), passes
the air through a counter-flow heat exchanger, which heats the air,
uses the heated air to drive an isothermal expander for power
generation, and passes the expander exhaust back through the
counter-flow heat exchanger to heat the input air to the expander.
Another embodiment has a boiler that produces vapor that flows
through a counter-flow heat exchanger to superheat the vapor. The
vapor then flows through an isothermal expander for power
generation. The exhaust from the isothermal expander flows back
through the counter-flow heat exchanger to supply heat to super
heat the vapor coming from the boiler. The description presents
several devices that can perform at near isothermal conditions,
including a modified Tesla turbine.
Inventors: |
Prueitt; Melvin L.; (Los
Alamos, NM) |
Correspondence
Address: |
Melvin L. Prueitt
161 Cascabel St.
Los Alamos
NM
87544
US
|
Family ID: |
39885383 |
Appl. No.: |
12/245224 |
Filed: |
October 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12104797 |
Apr 17, 2008 |
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12245224 |
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Current U.S.
Class: |
60/670 |
Current CPC
Class: |
F01K 27/00 20130101 |
Class at
Publication: |
60/670 |
International
Class: |
F01K 27/00 20060101
F01K027/00 |
Claims
1. An isothermal power generating system comprising: an isothermal
compressor for compressing a gas; a cooler, which supplies a
cooling fluid to the isothermal compressor to cool the gas flowing
through the isothermal compressor; a counter-flow heat exchanger
for heating the compressed gas; an isothermal expander for
expanding the heated compressed gas to produce mechanical power; a
heater for supplying a heating fluid to the isothermal expander to
heat gas flowing through the isothermal expander; and means for
conducting the expanded gas back through the counter-flow heat
exchanger to supply heat to the compressed gas flowing from the
compressor through the counter-flow heat exchanger; wherein the
isothermal compressor draws in and compresses cooled and expanded
gas flowing from the isothermal expander through the counter-flow
heat exchanger.
2. An isothermal power generating system according to claim 1,
wherein the isothermal compressor is an isothermal Tesla turbine
comprising: rotatable disks spaced along a shaft; a chamber within
each disk; input channels for conducting the cooling fluid from the
cooler into the chamber within each disk; and output channels for
conducting the cooling fluid out of the chamber within each disk
and returning the cooling fluid to the cooler; wherein the rotating
disks compress gas flowing between the disks, and wherein the
cooling fluid flowing through the chamber within each disk absorbs
heat from walls of the chamber, and wherein the chamber walls thus
absorb heat from the gas to maintain the gas at near isothermal
conditions, and wherein the cooling fluid flows from the chamber to
the cooler for further cooling.
3. An isothermal power generating system according to claim 2
further comprising disk supports for attaching the disks to the
shaft, and wherein the input channels are defined within the shaft
and within at least one of the disk supports, and wherein the
output channels are defined within at least one of the disk
supports and within the shaft.
4. An isothermal power generating system according to claim 2,
wherein: the cooling fluid is a liquid as it enters the chambers in
the disks and evaporates to cool the disks thereby to cool the gas
flowing between the disks; and wherein vapor produced by the
evaporation of the liquid flows through the output channels to the
cooler, where the vapor condenses back to a liquid.
5. An isothermal power generating system according to claim 1,
wherein the isothermal expander is an isothermal Tesla turbine
comprising: rotatable disks spaced apart along a shaft; a chamber
within each disk; input channels for conducting the heating fluid
from the heater into the chamber within each disk; and output
channels for conducting the heating fluid out of the chamber within
each disk and returning the heating fluid to the heater; wherein
the flow of expanding gas between the disks produces torque on the
disks to produce shaft power, and wherein the heating fluid flowing
into the chamber within each disk heats the walls of the chamber,
and wherein the chamber walls thus heat the expanding gas to
maintain the gas at near isothermal conditions, and wherein cooled
heating fluid flows out of the chamber back to the heater to be
reheated.
6. An isothermal power generating system according to claim 5
further comprising disk supports for attaching the disks to the
shaft, and wherein the input channels are defined within the shaft
and within at least one of the disk supports, and wherein the
output channels are defined within one or more of the disk supports
and within the shaft.
7. An isothermal power generating system according to claim 5,
wherein the heating fluid is a vapor as it enters the chambers in
the disks and condenses to heat the disks, thereby to heat the gas
flowing between the disks.
8. An isothermal power generating system according to claim 7,
wherein: liquid produced by the condensation of the vapor is forced
by vapor pressure to flow through radial tubes fluidly connected to
the output channels and extending away from the periphery and
toward the center of the chamber within each disk, and the liquid
flows through the output channels and returns to the heater where
it is boiled to a vapor, and the vapor flows back to the isothermal
expander.
9. An isothermal power generating system according to claim 7,
wherein: the liquid produced by the condensation of the vapor is
forced by vapor pressure to flow through a spiral tube running from
the outer periphery of the chamber in each disk to output channels
in the shaft, and as the liquid flows through the spiral tube
toward the output channels, it decelerates due to a decreasing
absolute speed of the liquid as the liquid approaches the disk axis
of rotation, and a deceleration force on the liquid promotes
movement of the liquid toward the output channels in the shaft, and
the liquid flows through the output channels and returns to the
heater where it is boiled to a vapor, and the vapor flows back to
the isothermal expander.
10. An isothermal power generating system for two-phase working
fluids comprising: a boiler for boiling a working fluid; a first
counter-flow heat exchanger for superheating working fluid vapor;
an isothermal expander for expanding the superheated working fluid
vapor to produce mechanical power; a heater for supplying a heating
fluid to an isothermal expander to heat the working fluid vapor
flowing through the isothermal expander; a means for conducting the
expanded working fluid from the isothermal expander back through
the first counter-flow heat exchanger to heat the working fluid
flowing from the boiler; a condenser for condensing the working
fluid vapor to a liquid; a pump for pumping working fluid into the
boiler; and a second counter-flow heat exchanger for preheating the
working fluid flowing to the boiler; wherein working fluid vapor
from the boiler flows through the first counter-flow heat
exchanger, and wherein the isothermal expander extracts mechanical
energy from the working fluid vapor as the working fluid vapor
expands, and wherein the working fluid flows back through the first
counter-flow heat exchanger and releases heat to superheat the
working fluid vapor flowing from the boiler, and wherein the
working fluid flows through the second counter-flow heat exchanger
to preheat the working fluid liquid, and the working fluid vapor
flows into the condenser to be condensed to a liquid, and wherein
the working fluid liquid is pumped through the second counter-flow
heat exchanger to the boiler.
11. An isothermal power generating system for two-phase fluids
according to claim 10, wherein the isothermal expander is an
isothermal Tesla turbine comprising: rotatable disks spaced along a
shaft; and a chamber within each disk; input channels for
conducting the heating fluid from the heater into the chamber
within each disk; and output channels conducting the heating fluid
out of the chamber within each disk and returning the heating fluid
to the heater; wherein a flow of working fluid between the disks
produces torque on the disks to produce shaft power, and wherein
the heating fluid flowing through the input channels and into the
chamber within each disk heats the walls of the chamber, which
chamber walls provide heat to expanding working fluid to maintain
the expanding working fluid at near isothermal conditions, and
wherein cooled heating fluid flows out of the chamber through the
output channels and back to the heater to be reheated.
12. An isothermal power generating system according to claim 11
further comprising disk supports for attaching the disks to the
shaft, and wherein the input channels are defined within the shaft
and within at least one of the disk supports, and wherein the
output channels are defined within one or more of the disk supports
and within the shaft.
13. An isothermal power generating system according to claim 11,
wherein the heating fluid is a vapor as it enters the chamber in
each disk, and the vapor condenses to provide heat to the disk
thereby to heat the working fluid flowing between the disks, and
wherein the liquid produced by the condensation of the vapor is
forced by vapor pressure to flow through tubes disposed radially in
the disk and fluidly connected to the output channels, and wherein
the liquid flows through the output channels and into the
heater.
14. An isothermal power generating system according to claim 11,
wherein: the heating fluid is a vapor as it enters the chamber in
each disk, and the vapor condenses to provide heat to the disk
thereby to heat the working fluid that is flowing between the
disks, and wherein the liquid produced by the condensation of the
vapor is forced by vapor pressure to flow through a spiral tube
running from the outer periphery of the chamber in each disk to
output channels in the shaft, and as the liquid flows through the
spiral tube toward the output channels, it decelerates due to a
decreasing absolute speed of the liquid as the liquid approaches
the disk axis of rotation, and a deceleration force on the liquid
promotes movement of the liquid toward output channels in the
shaft, and the liquid flows out through the output channels in the
disk supports and in the shaft and returns to the heater where it
is boiled to a vapor, and the vapor flows back to the isothermal
expander.
15. An isothermal power generating system according to claim 1,
wherein the isothermal compressor is an isothermal Tesla turbine
comprising: a set of closely spaced rotatable disks operatively
connected to a shaft by disk supports; a set of curved vanes on
outside faces of each disk, wherein the vanes comprise a spiral
configuration to guide the gas from the center of the turbine
toward the periphery of the turbine to increase compression of the
gas, and wherein the vanes further comprise surface area for
promoting heat transfer between the disk and the gas; a chamber
within each disk; input channels within the shaft and within at
least one of the disk supports for conducting the cooling fluid
from the cooler into the chamber within each disk; and output
channels within at least one of the disk supports and within the
shaft for conducting the cooling fluid out of the chamber within
each disk and for returning the cooling fluid to the cooler;
wherein the rotating disks aided by the curved vanes compress gas
flowing between the disks, and wherein the cooling fluid flowing
through the input channels in the shaft and disk supports into the
chamber within each disk absorbs heat from the walls of the
chamber, and wherein the chamber walls absorb heat from the
compressing gas to maintain the gas at near isothermal conditions,
and wherein the cooling fluid flows out of the chamber through
output channels in the disk supports and the shaft and back to the
cooler where it cooled and then returns to the isothermal
compressor.
16. An isothermal power generating system according to claim 1,
wherein the isothermal expander is an isothermal Tesla turbine
comprising: a set of closely spaced rotatable disks operatively
connected to a shaft by disk supports; a set of curved vanes on
outside faces of each disk, wherein the vanes comprise a spiral
configuration whereby gas flowing from the periphery of the turbine
toward the center of the turbine presses on the vanes to increase
torque on the shaft, and wherein the vanes comprise surface area
for promoting heat transfer between the disk and the gas; a chamber
within each disk; input channels within the shaft and within at
least one of the disk supports for conducting the heating fluid
from the heater into the chamber within each disk; and output
channels within at least one of the disk supports and within the
shaft for the purpose of conducting the heating fluid out of the
chamber within each disk and returning the heating fluid to the
heater; wherein the flow of gas between the disks imposes torque on
the disks and on the vanes, to produce shaft power, and wherein the
heating fluid flowing through the input channels in the shaft and
disk supports into the chamber within each disk heats the walls of
the chamber, and wherein the chamber walls provide heat to the
expanding gas to maintain the gas at near isothermal conditions,
and wherein the cooled heating fluid flows out of the chamber
through output channels in the disk supports and shaft back to the
heater to be reheated, and then to return to the isothermal
expander.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This Continuation in Part application claims priority to and
the benefit of U.S. patent Utility application Ser. No. 12/104,797,
filed Apr. 17, 2008, the entirety of which is hereby incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] Most of the heat engines in use today use adiabatic
expansion of gases to produce power. The Rankine, Brayton, Otto
cycles, and others use adiabatic expansions, and some of them also
use adiabatic compressions. This disclosure shows that isothermal
expansion and compression have some important efficiency
advantages.
[0003] The isothermal cycle can use a working fluid such as water,
ammonia, or propylene that are boiled and then expanded
isothermally in an engine to produce power. The vapors are then
condensed back to a liquid to repeat the cycle. It can also use a
gas such as air or helium that can be compressed isothermally,
heated, and then expanded isothermally in an engine that drives an
electric generator or drives some other machine. Since the exhaust
gas from the expander is still hot, its heat can be used to heat
the compressed gas flowing from the compressor to the expander.
[0004] Some U.S. Pat. Nos. that are somewhat related to embodiments
of the present invention are 4,023,366, 4,207,027, 4,455,825,
4,676,067, 5,641,273, 6,186,755, 6,205,788, 6,225,706, 7,062,913,
and 7,124,585.
SUMMARY OF THE INVENTION
[0005] In order to have isothermal compression and expansion of
gases, heat must be removed from the gas while it is being
compressed, and heat must be supplied to the gas during expansion.
One purpose of this invention is to provide means of transferring
heat to and from gases quickly.
[0006] By providing appropriate heat exchangers at appropriate
points in the design, the disclosed isothermal systems provide a
method that allows the exhaust from the expander engine to flow
through the heat exchangers to supply superheat for the vapor
flowing from the boiler or compressor to the expander engine. For a
two-phase fluid, the gas from the expander that flows through the
heat exchanger still has enough heat left over to partially preheat
the feed liquid flowing to the boiler. This cannot be done with an
adiabatic expander, because the vapor exhaust from the adiabatic
expander is normally cooler than the superheat temperature.
[0007] Another important feature of the isothermal engine is that
the same amount of gas can be expanded to much larger volumes than
the adiabatic machine, and this provides more output energy.
[0008] We can consider an example to compare the isothermal steam
engine with a Rankine cycle steam engine. As an example, suppose we
begin with liquid water and boil it at 400 K (127.degree. C.). If
one kilogram (0.731 m.sup.3) per second of steam flows from the
boiler at a pressure of 2.455 bar and is superheated to 800 K
(527.degree. C.), the power produced by an isothermal expander is
defined (for an ideal gas) by
W=P.sub.sV.sub.sln(V.sub.e/V.sub.s)
where P.sub.s is the pressure of the superheated gas (same as the
boiler pressure), V.sub.s is the volume of the superheated gas, and
V.sub.e is the volume of the expanded gas flowing out of the
expander. The "ln" is the natural log function. The volume V.sub.s
is 1.462 m.sup.3 (since the temperature is twice as high as the
boiling temperature at constant pressure). If we let the gas expand
in the isothermal expander to the condenser pressure, 0.03531 bar,
the vapor volume will be 101.65 m.sup.3, and the power will be
1.522 MW. The efficiency will be 38.77%.
[0009] For an adiabatic expander, the power is defined by
W=(P.sub.eV.sub.e-P.sub.sV.sub.s)/(1-.gamma.)
where .gamma. is the ratio of specific heats of the gas. For this
example, we let .gamma.=1.32. If we let the superheated gas expand
adiabatically to P.sub.e=0.03531 bar (same as in the isothermal
case), the volume will be only 36.35 m . The power will be 0.72 MW.
This is only 47% of the power output by the isothermal system. The
isothermal case requires 15% more heat input, but it uses that heat
more efficiently. The efficiency of the adiabatic (Rankine) cycle
is 21.16%.
[0010] For an ideal gas, the internal energy depends only on the
temperature. Thus, all the heat input to the isothermal engine is
used to generate power as it maintains the gas temperature at a
constant value (no change in internal energy of the gas). Then,
when the gas is exhausted from the expander, it is still at the
same temperature as the input temperature, and its energy can be
used to superheat the boiler vapor in the counter-flow heat
exchanger as its temperature theoretically drops down to the boiler
temperature. In an actual machine, we would want the input heat to
the isothermal engine to be at a little higher temperature than the
superheat temperature in order to provide the temperature
differential to cause adequate heat flow.
[0011] For the adiabatic case, after the gas expands to 36.35
m.sup.3, its temperature is only 286 K, which is too cold to supply
any heat to superheat the gas flowing out of the boiler.
[0012] The following table gives some calculated values for the
performance of the isothermal heat engine that uses steam as the
working fluid. These calculations were made by a computer
TABLE-US-00001 TABLE I Isothermal Boiler Condenser Superheat Engine
Rankine Rankine Temperature Temperature Temperature Power
Efficiency Cycle Eff. Cycle with (Degrees C.) (Degrees C.) (Degrees
C.) (MW) (%) (%) Reheat, Eff. 80 27 90 0.446 15.53 9.81 10.52 127
27 227 0.951 28.35 16.05 17.82 127 27 727 1.903 44.18 23.70 25.10
200 27 700 2.577 52.47 27.68 30.21 300 27 800 2.760 56.80 25.66
27.98 300 27 1000 3.276 60.94 27.46 29.61 200 27 1000 3.371 59.10
31.15 33.39 300 27 1200 3.900 64.36 28.95 30.93 22 12 27 0.095 3.68
2.66 22 12 127 0.126 4.86 3.28 22 12 227 0.158 6.00 3.82 22 12 480
0.237 8.77 4.90 22 12 800 0.339 12.05 5.88
program called "Isoengine.exe." For comparison, the
next-to-the-last column gives the efficiency of an ordinary Rankine
cycle steam engine. The last column gives the performance of a
Rankine cycle steam engine with single reheat. The power values are
for a flow of one kilogram per second of steam. The values in the
Rankine columns were calculated with a single gamma value and
constant heat capacity of the steam, which provide slightly
inconsistent values, since the gamma varies with temperature and
pressure. The values in the table are theoretical values, but the
comparison between the isothermal engine and the Rankine steam
engines is valid.
[0013] The first row in the table represents values that would be
appropriate for a system that uses heat from a solar pond where the
temperature of the pond might be 90.degree. C.
[0014] The last five rows are for OTEC applications. No
multi-staging is involved. Efficiencies could be higher if
multi-stages were used. The Rankine cycle with reheat is not listed
for these five rows, because the temperature differences are too
small to use reheat.
[0015] Using a system that has isothermal compression and expansion
of single-phase gases provides performances that are even better
than isothermal system of the two-phase fluids, such as water-steam
(Rankine cycle). Air can be used as the working fluid. Helium has
high heat transfer properties and might be used. It is used in
Stirling engines.
[0016] Table II gives some calculations of performance for this
design that were made by a program called "Isotherm5.exe." Again,
these are theoretical calculations that do not include friction and
thermal conduction losses. For each item in the table, the air
pressure at the entrance to the isothermal compressor is 10 bar,
the temperature is 27.degree. C., and the volume is 1 cubic meter
per second. The air is compressed in the compressor to 0.2
m.sup.3.
[0017] Note that at the same temperatures of superheat, the
efficiencies for this apparatus with an isothermal compressor and
an isothermal expander are significantly higher than those for the
device that has a boiler and an isothermal expander, as shown in
Table I. In fact, when the single-phase simulations were run with
the computer program, the efficiencies turned out to be Carnot
efficiencies. When friction and heat conduction losses are
included, the efficiencies will be less, but they should still be
higher than the devices in Table I, when losses are included in
those calculations.
TABLE-US-00002 TABLE II Superheat Temperature Power Output
Efficiency (Degrees C.) (MW) (%) 100 0.3916 19.57 200 0.9281 36.58
300 1.4650 47.64 400 2.0010 55.40 500 2.5375 61.19 600 3.0740 65.65
700 3.6105 69.17 800 4.1470 72.04 900 4.6835 74.43 1000 5.2199
76.43 1200 6.2929 79.63
[0018] It is therefore an object of the present invention to
provide an economical means of producing power using isothermal
compressors and isothermal expanders.
[0019] It is another object of the present invention to utilize
available heat sources to provide energy to generate electrical
power using isothermal compression and expansion engines.
[0020] It is another object of the present invention to utilize
available heat sources to provide energy to generate electrical
power using a boiler and an isothermal expansion engine.
[0021] It is another object of the present invention to utilize
available heat sources to provide the heat required to maintain
near-isothermal conditions in isothermal expanders.
[0022] It is another object of the present invention to utilize the
hot exhausts gas from an isothermal expander to superheat the
compressed gas from an isothermal compressor in a counter-flow heat
exchanger.
[0023] It is another object of the present invention to utilize the
hot steam, or other two-phase working fluid, that exhausts from an
isothermal expander to superheat the vapor from a boiler in a
counter-flow heat exchanger.
[0024] It is another object of the present invention to provide
means for reducing mechanical losses in the compression and
expansion devices.
[0025] It is another object of the present invention to provide
methods to effectively produce substantially isothermal compression
and expansion of gases.
[0026] It is another object of the present invention to provide an
efficient Tesla-like turbine that operates isothermally.
[0027] 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 DRAWINGS
[0028] 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:
[0029] FIG. 1 is a schematic side view of an embodiment of an
apparatus according to the present disclosure showing an isothermal
compressor, an isothermal expander, a counter-flow heat exchanger,
a heater, and a cooler.
[0030] FIG. 2 is a schematic side view of an embodiment of an
apparatus according to the present disclosure that illustrates the
use of a boiler, counter-flow heat exchangers, an isothermal
expander, a heater, and a condenser.
[0031] FIG. 3 is a schematic sectional side view of an embodiment
of an isothermal compressor or isothermal expander according to the
present disclosure, which has a piston in a cylinder and has
tapered plates that transfer heat to and from the gas.
[0032] FIG. 4 is a schematic isometric view of another embodiment
of an apparatus according to the present disclosure, having tapered
concentric circular forms for increasing surface contact with gases
for isothermal compressors and expanders.
[0033] FIG. 5 is a graphic depiction of an inside top view of a
rotating piston engine according to the present disclosure.
[0034] FIG. 6 is a schematic top view of a modified rotating piston
engine according to the present disclosure, featuring tapered
plates for isothermal operation.
[0035] FIG. 7 is a schematic end view of another embodiment of an
apparatus according to the present disclosure, showing the stator
blades of an isothermal turbine.
[0036] FIG. 8 is a schematic end view of a rotor blade of an
isothermal turbine, such as may be used in the embodiment seen in
FIG. 7.
[0037] FIG. 9 is a schematic side view of an embodiment of a
bellows compressor and/or expander according to the present
disclosure.
[0038] FIG. 10 is an axial or end view of a cross section of an
isothermal Tesla turbine compressor according to the present
disclosure.
[0039] FIG. 11 is a cross-sectional side view of two disks mounted
on the shaft of an isothermal Tesla turbine compressor, as may be
used in the embodiment seen in FIG. 10.
[0040] FIG. 12 is an end view schematic of the cross section of an
isothermal Tesla turbine expander.
[0041] FIG. 13 is an axial or end view of a cross section of a disk
of an isothermal Tesla turbine expander showing a method of
reducing the vapor pressure required to remove the heating liquid
from the disk chamber.
[0042] FIG. 14 is an end view schematic of a disk showing curved
vanes attached to the side of the disk.
DETAILED DESCRIPTION OF THE INVENTION
Single-Phase Gas Isothermal Heat Engine
[0043] FIG. 1 shows a layout for the single-phase gas isothermal
engine system. The gas is compressed in the isothermal compressor
120. In order to keep the gas at constant temperature, a cooler 128
is necessary, since compression of a gas tends to heat it.
[0044] For efficient heat transfer, the cooler 128 can supply a
liquid to channels beneath the surfaces in the compressor 120. The
liquid evaporates as it removes heat from the surfaces. The vapor
flows to the cooler 128, where it is condensed and returned to the
compressor 120.
[0045] For adequate heat flow, a heater 127 should supply heat at
slightly higher temperature than the isothermal temperature of the
expander 123, and the cooler 128 should supply a fluid that is at
slightly lower temperature than the compressor isothermal
temperature.
[0046] In FIG. 1, the isothermal compressor 120 draws air (or other
gas) in through pipe 126 and compresses it. The compressed gas from
the isothermal compressor then flows through the counter-flow heat
exchanger 122, where it is heated by the exhaust from the
isothermal expander 123. After the gas leaves the heat exchanger
122, it flows through the isothermal expander 123 to produce power,
which drives electrical generator 130. The exhaust gas from the
isothermal expander 123 flows back through the counter-flow heat
exchanger 122 and returns to the isothermal compressor 120 to
repeat the cycle.
[0047] For this design, the cooler 128 keeps the compressor 120
cool. The cooler 128 could use water-cooling, evaporative cooling,
or even ambient air to dispose of the heat. The isothermal expander
123 is kept hot by heater 127. The heat can be supplied by solar
energy, fossil fuels, nuclear energy, geothermal, or other heat
source.
Steam Isothermal Power Generator
[0048] An isothermal expander can be used to produce power with
steam (or other two-phase working fluid). In FIG. 2, steam is
produced in boiler 140. The steam flows through a counter-flow heat
exchanger 141, which superheats the steam. From there, the steam
flows through an isothermal expander 142, which produces power by
the steam expansion and drives the generator 148. Since the
expander is isothermal, there would be no problem with steam
condensation. After the steam leaves the expander 142, it flows
back through the counter-flow heat exchanger 141 where its
temperature decreases as it provides heat to superheat the steam
coming from the boiler 140.
[0049] Exiting the first counter-flow heat-exchanger 141, the steam
still has sufficient heat to preheat the boiler feed water in a
second counter-flow heat exchanger 143. The steam is then condensed
in the condenser 144. The condensate is then pumped by pump 146
back into the boiler 140 through counter-flow heat exchanger
143.
[0050] Even though the engine is called "isothermal," in order to
have heat transfer into the expanding steam, the fluid flowing from
the heater 147 is at a higher temperature than the "isothermal"
temperature. The steam flowing out of the isothermal engine 142 is
hotter than the steam coming from the counter-flow heat exchanger
141.
Designs for Isothermal Compressors and Expanders
[0051] In my co-pending U.S. patent application Ser. No. 11/739,580
entitled "Water Extraction from Air and Desalination," incorporated
herein by reference, some designs for isothermal compressors and
expanders are described. Some of the drawings and descriptions from
that disclosure are provided here to show some types of isothermal
engines that can be used to keep the gases close to isothermal.
[0052] FIG. 3 schematically illustrates an isothermal compressor or
expander. To increase heat transfer from the gas to the metal, the
metal surface area is greatly increased by placing components such
as tapered plates 22 on the front of the piston 21 and
complementary tapered plates 23 on the bottom of the isothermal
engine cylinder 20, leaving channels for gas flow. (The piston and
cylinder combination is referred to as an "isothermal engine,"
because it may function either as a compressor or as an expander).
These components 22, 23 could have planar surfaces as shown in FIG.
3. Alternatively, the components 38 could have circular concentric
configurations extending from a base 39, as seen in FIG. 4.
[0053] In operation as a compressor, as the piston 21 in the
isothermal engine 20 moves upward, it draws in air (or other gas)
through check valve 26. When the piston 21 reaches its maximum
height, valve 26 closes, and the piston is forced downward,
compressing the gas. As the gas is compressed, it tends to increase
in temperature, but the tapered plates 22, 23 absorb the heat of
the gas. Since the heat capacity of the metal plates is about 2000
times greater than the gas (per unit volume), the temperature of
the plates 22, 23 does not rise very much during one half
cycle.
[0054] When the piston 21 has traveled down far enough to provide
the appropriate pressure the gas, check valve 36 opens to allow the
gas to flow out. The piston 21 continues to move downward to force
the compressed gas out.
[0055] When the apparatus is in operation as an expander, check
valve 26 is replaced by a controlled valve. As the piston 21 in the
cylinder 20 moves upward, it draws in air (or other gas) through
controlled valve 26. When the piston reaches the designed height,
valve 26 closes, and the piston continues to rise, expanding the
gas and extracting energy from the gas. As the gas is expanded, it
tends to decrease in temperature, but the tapered plates 22, 23
provide heat for the gas. When the piston 21 moves downward, it
forces the gas out through check valve 36.
[0056] For the compressor, the tapered plates 22, 23 can have
interior channels in which a cooling fluid can flow. The cooling
fluid could be a liquid that evaporates to absorb the heat. For the
tapered piston plates 22, the fluid would have to be delivered and
retrieved through channels in the piston rod 27. The fluid can be
delivered to tapered cylinder plates 23 through channels in the
cylinder 20. Calculations show that the gas will remain near
isothermal during both compression and expansion, since the gas has
close proximity to the plates 22, 23 for heat transfer, and the
motion of the plates create turbulence that further enhance heat
transfer.
[0057] For the expander, heating fluids are required. The heating
fluids could be gas or liquid, or they could be vapor that
condenses to a liquid in the channels of the tapered plates to
release the heat of condensation.
[0058] In this disclosure, components that are used to increase the
surface area in contact with the working gas are mostly referred to
as "tapered plates," because it is easy to illustrate the tapered
plates in the drawings. Heat-transfer components having other
shapes and configurations may be contemplated, and are within the
scope of the invention. In many applications, it may be better to
use tapered concentric circular forms that are approximately
cylindrical. FIG. 4 shows the tapered concentric circular forms 38
mounted on a base 39. Such circular forms 38 would fit better in a
cylinder (such as cylinder 20 in FIG. 3) than would planar plates.
Thus, the tapered plates 23 seen in FIG. 3 could actually be the
tapered concentric circular forms 38. Similar complementary
arranged circular forms could be attached to piston 21 in FIG. 3.
The radii of the upper circular forms and the lower circular forms
must be defined so that the circular forms "mesh" or fit together
as the piston descends.
More Efficient Compressors and Expanders
[0059] One of the main sources of inefficiency for a compressor or
expander that is needed for the isothermal engine is sliding
friction of the piston. My U.S. Pat. No. 6,401,686, which is
incorporated herein by reference, discloses an apparatus referred
to as "MECH," which stands for motor, expander, compressor, and
hydraulics. As the MECH apparatus 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 relative to their diameters.
[0060] It is well known that rolling friction is only about 1/100
as large as sliding friction. A MECH prototype 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.
[0061] FIG. 5 depicts a MECH engine 65 with an end plate removed to
reveal how the two rotating pistons 66 roll together at the contact
line 67. The engine 65 could be used as a compressor or as an
expander. Cavities 68 and 69 within the engine 65 are locations in
which gases are compressed or expanded. Similar cavities are
present on the other side of the engine next to the other rotating
piston.
[0062] FIG. 6 shows a top view of a compressor/expander 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 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 to the gas
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 ends of
the cylinders. The seal to prevent gas leakage is formed at the
rolling contact point between the two pistons.
[0063] FIG. 6 is a schematic top view of such 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
partition 74. Tapered plates 72, similar to those in FIG. 3, are
placed inside the rotating piston 71. (FIG. 6 shows a top view of
the plates, whereas FIG. 3 shows the plates edge-on). The top and
bottom of the rotating piston are closed with half-circle plates;
they are not shown, because they are on the near end and far end of
the half-cylinder (i.e., above and below the plane of the page).
When the right piston rotates to the right and the left piston
rotates to the left, the upper tapered plates 72 will move into the
volume where stationary tapered plates 73 are located and will fit
between the stationary plates. The gas in the spaces will be
compressed and squeezed out (for a compressor) the exhaust/intake
pipes 76. At the same time, gas will be drawn into the bottom half
of the engine through the pipes 78. When it rotates the other
direction, gas in the bottom half will be compressed. For an
expander, the gas is drawn in, expanded, and pushed out.
[0064] The tapered plates 72, 73 provide large surface areas for
the transfer of heat to and from the gas. The motion of the tapered
plates 72 relative to the stationary plates 73 causes gas
turbulence in the small gaps between them to enhance heat flow.
[0065] In order for the expander or compressor of FIG. 6 to perform
isothermally, heating or cooling fluid needs to be supplied to the
surfaces inside the device. To supply heating or cooling fluid to
the rotating tapered plates 72, the fluid can flow through an axial
hole in the center of the shaft 77 and flow through channels in the
rotating plates to cool or heat the rotating plates. After the
fluid flows through the channels, it flows back to near the other
end of the shaft 77 and enters a hole in the shaft allowing the
fluid to exit the other end of the shaft. The stationary plates 73
can receive fluid through the separator 79. The walls can have
fluid channels on the outside.
[0066] Instead of flat tapered plates, this embodiment of the
invention could use tapered concentric circular forms as described
above and illustrated in FIG. 4. In this case, the circular forms
would not be complete circles, but would be partial circular
configurations.
Isothermal Turbines
[0067] In an isothermal turbine expander, the heating fluid can
flow through the turbine walls, stator blades, and rotating blades.
Reference is made to FIG. 7 showing an expander. Although there are
cases in which the heating fluid can be a liquid or a gas, in the
following disclosure, the heating fluid enters as a vapor and
condenses to release the latent heat of condensation. FIG. 7 is a
schematic drawing showing the stator blades and the flow paths of
the heating fluid. The hot vapor flows in the inlet pipe 161 into
the top of the turbine 160, and flows through a vapor channel 162
on the upper half of the turbine. It flows through channels (not
shown) within the upper stator blades 163 toward the center of the
turbine. The turbine shaft 169 is at the center of the turbine.
Part of the vapor condenses and releases the latent heat of
condensation. The condensed liquid and the remaining vapor flow
into the vapor and liquid channel 164.
[0068] From there, the vapor and liquid flow to the lower stator
blades 165 and flow through channels in those blades. In the stator
blade channels, more of the vapor condenses. The liquid and the
remaining vapor flow into the liquid channel 166 on the lower half
of the turbine. They return to the heating fluid boiler (not shown)
through the condensed liquid outlet 167. After boiling, the vapor
returns again to the isothermal expander turbine.
[0069] For an isothermal turbine compressor, the geometry looks
much like the expander of FIG. 7. The cooling liquid enters from
the top 161. It is designed so that the liquid is directed into
each of the upper stator blades. As the liquid flows down through
channels in the blades, some of it evaporates and provides cooling
by the latent heat of evaporation. The vapor and the remaining
liquid flow to the vapor and liquid channel near the center of the
turbine. Appropriate guides are designed to direct liquid into each
of the lower stator blades. The vapor flows along with the liquid.
More liquid vaporizes in the lower stator blade channels.
[0070] Finally, the vapor and any remaining liquid flow out the
bottom and flow back to a cooler, which condenses the vapor to a
liquid. The liquid is pumped back to the turbine compressor to
repeat the cycle.
[0071] Alternatively, the liquid can be pumped into the bottom of
the compressor. As it flows up through the lower stator blades, it
boils. The vapor it creates blows liquid as a mist up through the
rest of the system. The mist droplets strike surfaces and
evaporate, removing heat and continuing the process of blowing
liquid droplets up through the upper blades.
[0072] If the stator blades do not provide sufficient heat removal
for the compressor, the rotating blades may be configured to
receive liquid that evaporates and removes heat. The liquid enters
one end of the shaft that holds the turbine blades. The liquid then
flows through a channel in the shaft until it reaches the channels
in the blades. As it flows through the blade channels, it
evaporates and removes heat. The vapor flows back to the shaft and
flows through another channel in the shaft to the other end of the
shaft and then flows back to the cooler.
[0073] It is not so simple for an isothermal expander turbine. If
vapor is put into the rotating blades, it condenses to a liquid,
which has high density. Centrifugal force causes the liquid to move
to the tips of the blades. High pressure is required to force the
liquid back to the shaft against the centrifugal force. The density
of the liquid can effectively be reduced by mixing it with the
vapor. By supplying more vapor than is necessary to deliver the
required heat, the extra vapor flows back to the shaft through a
small-diameter channel and carries with it a mist of liquid.
[0074] A schematic drawing of a single rotating turbine blade 180
for an expanding turbine is shown in FIG. 8. Hot vapor flows from
one end of shaft 181 through channel 182 inside the shaft 181 to
the vapor channel 183 and flows through vapor channel 183 in the
blade. Part of the vapor condenses in the vapor channel and
releases heat to keep the blade hot. The condensed liquid flows by
centrifugal force to the space 184 near the end of the blade. The
vapor at high pressure is forced to flow through the small-diameter
liquid and vapor return pipe 185 at high speed back to the shaft
and into the liquid and vapor output channel 186. Since it is
flowing at high velocity, it will carry a mist of liquid with it.
The vapor and the liquid will flow through the channel 186 to the
other end of the shaft, where they will flow into a coupling that
takes the vapor and liquid back to the boiler.
[0075] Another alternative would be to use a liquid to transfer
heat to the rotating blades. The liquid flowing from the shaft to
the tip of the blade would provide the pressure to push the liquid
back to the shaft. The liquid flowing back to the shaft would be
slightly denser than the liquid flowing toward the tip, because it
is cooler. Extra pressure in the input channel would be
required.
[0076] In order to enhance the heat transfer between the turbine
blades and the gas, the blades should probably be closer together
and be wider than blades in standard turbines.
Other Isothermal Designs
[0077] FIG. 9 shows a compressor/expander design that incorporates
bellows 83 to compress and expand gas. The bellows is connected to
the top 80 and to a base 85. Push rod 81 moves the top up and down.
The purpose of the displacer 84 is to push out as much gas as
possible when the bellows is compressed as far as possible. Gas
flows in and out of pipe 86.
[0078] For an isothermal compressor, the tapered plates like those
of FIG. 3 can be connected to the displacer 84 and to the base 85.
Rather than use flat tapered plates, it would probably be better to
use tapered concentric circular forms as illustrated in FIG. 4.
[0079] If we can increase the efficiency of standard power
generating plants by replacing the adiabatic engines with
isothermal engines, it would reduce the release of greenhouse gases
into the atmosphere. For solar thermal or geothermal power plants,
the isothermal engines would produce more power for the same size
heat source.
Isothermal Tesla Turbine
[0080] The Tesla turbine allows the flow of gas between rotating
disks to transfer momentum between the gas and the disks. The Tesla
turbine expander produces power from the flow of compressed gas as
the gas expands, while the Tesla turbine compressor pumps gas from
low pressure to high pressure. Since it provides large surfaces
that are exposed to the gas, it would be ideal for isothermal use,
but the Tesla turbine requires special modifications, as now
described.
[0081] U.S. Patent Application Publication number US 2005/0172624
A1, entitled "Method and Device for Converting Thermal Energy into
Kinetic Energy," by Holecek, et al., describes several methods of
compressing and expanding a gas to produce power. The Holecek et
al. application mentions that with a Tesla turbine, in particular,
better isothermal expansion or compression is possible. But the
Holecek et al. application does not describe how to make a Tesla
turbine "isothermal." Normally the gas in a Tesla turbine expands
or compresses nearly adiabatically. Methods must be provided to
remove heat from a gas that is being compressed or to add heat to a
gas that is expanding.
[0082] A Tesla turbine features of a number of closely spaced disks
that rotate about a shaft in a cylindrical enclosure. In a Tesla
turbine expander, the compressed gas flows into the housing
tangential to the outside edges of the disks and flows between the
disks as it imparts energy to the disks by transfer of momentum.
The gas flows out through holes in the disks near the shaft. In a
compressor, gas flows in through the holes in the disks and is
compressed as it flows outward toward the periphery of the
disks.
[0083] FIG. 10 provides a cross-sectional end view of one of the
disks 101 of a Tesla turbine compressor 100. Each disk defines in
its interior a narrow hollow chamber 102, which may be referred to
as a "disk chamber." To define the disk chamber 102, the disk 101
may be formed by two disks that are sealed together at their outer
edges and sealed near their centers where the disk supports 103
connect the disk 101 to the shaft 104. A cooling fluid flows
through a channel 105 from one end of the shaft and flows through
the disk supports 103 via the fluid distributor pipe 106 into the
narrow disk chamber 102. After absorbing heat, the cooling fluid
flows out the outlet pipe 107 to the exit channel 108 in the shaft.
From there, the fluid flows to the opposite end of the shaft 104
from the end where the fluid entered and flows back to the cooler
128 of FIG. 1.
[0084] One effective method of transferring a large quantity of
heat is to use a liquid to flow into the disk chamber 102. The
liquid spreads over the inside walls of the chamber as it is thrown
outward by centrifugal force. The liquid evaporates and removes
heat from the chamber walls. The amount of heat removed is
equivalent to the latent heat of evaporation of the liquid. This
cools the gas that is flowing outside the disks.
[0085] The vapor from the evaporating liquid flows to the outlet
pipe 107 and then flows into a fluid exit channel 108. From there,
it flows to the end of the shaft opposite the end where the liquid
enters, and is transmitted via a sealed connection that takes the
vapor to a cooling unit. The fluid is condensed in the cooling unit
and pumped back to the turbine 100 to flow again in the liquid
entry channel 105.
[0086] The gas that is being compressed enters through gas entry
ports 109 between the disk supports and after flowing radially
outward between the rotating disks, it flows out the gas exit port
110.
[0087] FIG. 11 is longitudinal cross section view of selected
internal parts of the isothermal Tesla turbine compressor. The
shaft 104 runs from left to right. For simplicity of illustration,
only two disks 101 are shown. A complete Tesla turbine has at least
two and preferably a number of disks mounted for rotation on or
with the shaft 104. The cooling fluid flows through pipe 114 into
the shaft and flows through the cooling fluid entry channel 105. It
flows into the disk chambers 102 through the fluid distributor
pipes 106, which are not shown in FIG. 11, because they are
perpendicular to the page of the drawing. After absorbing heat, the
fluid flows out the fluid outlet pipes 107 and then flows through
the fluid exit channels 108 to the right end of the shaft and exits
pipe 115. From there it flows back to the cooler, where it will be
condensed and pumped back to the compressor.
[0088] FIG. 12 is a schematic showing an end view cross section of
one of the disks of a Tesla turbine expander. It may look very
similar to the compressor disk if a single-phase liquid or gas is
used for heat removal (in the compressor) or heat deposit (in the
expander). In this case, the pressurized gas enters the cylinder
via the entry ports 150 and flows tangentially to the edges of the
disks 101 and flows between the disks as it imparts rotational
energy to the disks. The gas expands as it flows radially inward
between the disks to the gas exit ports 151. As the gas expands, it
tends to cool. In order to maintain it substantially near
isothermal conditions, heat must be supplied. A hot fluid is pumped
through the disk chamber 102 to keep the disk surfaces hot and
transfer heat to the gas.
[0089] One embodiment of the apparatus utilizes a vapor flowing
through a vapor entry channel 149 and vapor injector tube 154 into
the disk chamber 102 of the expander. As the vapor condenses, it
releases heat to the walls of the chamber. The condensed liquid is
heavy and is thrown radially outward toward to the outer part of
the chamber 102. FIG. 12 illustrates extended liquid collector
tubes 152 to collect the liquid where it accumulates near the
peripheral rim of the disk. If the incoming vapor has sufficient
pressure, the liquid will be forced to flow through the liquid
collector tubes 152 to the liquid exit channel 153 in the shaft,
and then flow to a heater where the liquid is pumped into a boiler,
which boils the liquid. The vapor then flows back to the
expander.
[0090] If the liquid filled tube runs from the center of the shaft
to the outside of the disk chamber, the pressure at the outer end
of the tube is
P=0.5 .rho.v.sup.2
where P is the pressure in Pascals, .rho. is the density in
kilograms per cubic meter, and v is the velocity of the end of the
tube in meters per second. If the disk is rotating at 12,000 rpm
and the outer end of the tube is 10 centimeters from the center of
the shaft and the density is that of water, the pressure is 7.896
MPa (1,145 psi). It might be difficult to provide the appropriate
pressure to force the liquid out of the disk chamber.
[0091] A solution is to have the liquid collector tube 152 have a
small inside diameter and provide more vapor than is necessary
during operation. The liquid droplets moving radially inward in the
tube are mixed with vapor so that the average density is reduced.
Thus, less vapor pressure is required to move the liquid toward the
shaft.
[0092] Another solution is to design the liquid collector tube 156
with a spiral shape, as shown in FIG. 13. As the liquid 155 enters
the outer end of the tube 156 and starts to flow toward the center
of the shaft, due to the vapor pressure, the liquid has to slow
down, because portions of the tube closer to the disk axis of
rotation (e.g., at the shaft) move more slowly than portions
farther from the rotational axis. This deceleration generates a
force that promotes movement of the liquid toward the shaft 104.
Thus, as the liquid flows through the spiral tube 156 toward the
output channel 153, it decelerates due to the decreasing absolute,
or linear, speed at which the part of the tube adjacent to the
liquid moves as the liquid approaches the disk's axis of rotation.
This progressively decreasing speed results from the fact that
those portions of the tube having a relatively smaller radius
(measured from the axis of rotation) move more slowly than those
portions having a larger radius. Stated differently, an axiom from
rotational dynamics dictates that the closer a point on a rotating
body is to the body's axis of rotation, the slower is that point's
movement speed in a frame of reference exterior to the body itself.
The resulting deceleration force on the liquid promotes movement of
the liquid 155 toward the output channel 153 in the shaft 104.
[0093] FIG. 1 shows the layout of the complete isothermal engine,
which could use isothermal Tesla turbines. The compressor 120
compresses the gas at near isothermal conditions as the fluid from
the cooler 128 removes the heat of compression. The compressed gas
flows through a counter flow heat exchanger 122 that heats the gas.
It then flows into the expander 123 where it expands as it
generates power that turns the generator 130 and the compressor.
The fluid from the heater 127 keeps the gas hot in the
expander.
[0094] The gas is still hot as it leaves the expander. It flows to
the heat exchanger 122 where it delivers its heat to the gas coming
from the compressor. The cooled gas then returns to the compressor
to repeat the cycle.
[0095] The heater can be any heat source, such as solar energy,
geothermal energy, fossil fuel, or nuclear energy. The cooler can
be a cooling tower, air cooler, or any source of cool water.
[0096] The isothermal Tesla turbine expander can also be used in a
two-phase working fluid engine with a boiler as shown in FIG. 2. In
this case, a compressor is not needed. The isothermal Tesla
expander is 142 in FIG. 2. A detailed description of FIG. 2 is
provided previously herein.
[0097] FIG. 14 shows a method of providing higher performance of a
Tesla-like turbine. Curved vanes 170 on outer faces of the disks
extend axially between disks 101 to provide additional surface area
to promote heat transfer between the disks and the fluid flowing
between them for both the compressor and the expander turbine
modes. The vanes 107 also help to guide the gas flow between the
disks 101. For the expander turbine, the gas flowing from the outer
periphery of the disk 101 toward the center imposes a rotational
torque on the vanes, which increases the power delivered to the
shaft. For the compressor turbine, the vanes impart a force on the
gas to more effectively pump the gas.
[0098] The vanes 107 are mounted on or attached to at least one
surface of the disk 101, and extend axially to the adjacent disk to
contact the face of that disk. Alternatively, vanes 107 could
extend axially from both sides of all disks, in which case
corresponding vanes on respective disks may contact each other.
Additionally, the vanes 107 optionally may extend radially inward
onto the disk supports 103.
[0099] Although an apparatus and method have been described in
detail with particular reference to these preferred embodiments,
other embodiments can achieve the same results. Variations and
modifications of the present disclosure will be obvious to those
skilled in the art and it is intended to cover in the appended
claims all such modifications and equivalents. The entire
disclosures of all patents and publications, cited above are hereby
incorporated by reference.
* * * * *