U.S. patent application number 11/592683 was filed with the patent office on 2007-07-19 for dual thermodynamic cycle cryogenically fueled systems.
This patent application is currently assigned to MeV Technology, Inc.. Invention is credited to Michael D. Strathman.
Application Number | 20070163261 11/592683 |
Document ID | / |
Family ID | 38023872 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163261 |
Kind Code |
A1 |
Strathman; Michael D. |
July 19, 2007 |
Dual thermodynamic cycle cryogenically fueled systems
Abstract
Systems and methods for converting thermal energy, such as solar
energy, from a localized thermal energy source to another form of
energy or work comprise dual thermodynamic cycle systems that
utilize the liquid-to-gas phase transitions of a cryogenic fluid
such as liquid nitrogen and a working fluid such as sulfur
hexafluoride to drive prime movers. Heat transfer between the
fluids as they undergo the phase transitions is used to increase
the energy in the system and its work output, and improve system
efficiency.
Inventors: |
Strathman; Michael D.; (San
Jose, CA) |
Correspondence
Address: |
LAW OFFICES OF BARRY N. YOUNG
260 SHERIDAN AVENUE
SUITE 410
PALO ALTO
CA
94306-2047
US
|
Assignee: |
MeV Technology, Inc.
|
Family ID: |
38023872 |
Appl. No.: |
11/592683 |
Filed: |
November 3, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60735056 |
Nov 8, 2005 |
|
|
|
60737682 |
Nov 17, 2005 |
|
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Current U.S.
Class: |
60/651 ;
60/659 |
Current CPC
Class: |
F03G 6/068 20130101;
F01K 23/18 20130101; F01K 25/10 20130101; F03G 6/00 20130101; F01K
25/085 20130101; F01K 23/00 20130101; Y02E 10/46 20130101 |
Class at
Publication: |
060/651 ;
060/659 |
International
Class: |
F01K 25/08 20060101
F01K025/08; F01K 3/00 20060101 F01K003/00 |
Claims
1. A method of converting thermal energy comprising: transferring
thermal energy into a cryogenic fluid from a first portion of
working fluid to expand the cryogenic fluid and create a first gas
and to convert the first portion of working fluid to a working
liquid; transferring thermal energy into a second portion of the
working fluid to expand the second portion of the working fluid and
create a second gas; utilizing the second gas to operate an energy
conversion apparatus; transferring additional thermal energy to the
first gas from exhausted second gas from the energy conversion
apparatus to increase the energy in the first gas; and utilizing
the first gas with said increased energy to operate another energy
conversion apparatus.
2. The method of claim 1, wherein said transferring of additional
thermal energy to the first gas comprises substantially reducing
the temperature of said exhausted second gas by a heat exchange
between said first and exhausted second gasses.
3. The method of claim 2, wherein said transferring of additional
thermal energy comprises flowing said first gas and said exhausted
second gas through a common heat exchanger that provides thermal
communication between said gasses.
4. The method of claim 1, wherein said cryogenic fluid comprises
cryogenic fluid from a cryogenic liquid reservoir, said first
portion of working fluid comprises said exhausted second gas, and
wherein said transferring thermal energy into said cryogenic fluid
comprises extracting said thermal energy from the exhausted second
gas to create said first gas.
5. The method of claim 4, wherein said extracting thermal energy
comprises transferring heat from said exhausted second gas to
condense said exhausted second gas to said working liquid.
6. The method of claim 1, wherein said transferring thermal energy
into a cryogenic fluid comprises transferring heat from said first
portion of working fluid into a cryogenic liquid in a
reservoir.
7. The method of claim 1, wherein said transferring thermal energy
into said second portion of working fluid comprises expanding said
second portion of working fluid in an atmospheric boiler.
8. The method of claim 7 further comprising adding heat to said
atmospheric boiler from a heat collector to increase the
temperature of said atmospheric boiler above ambient.
9. The method of claim 1, wherein said portions of working fluid
comprise working fluid in different parts of a closed system that
operates on a first thermodynamic cycle.
10. The method of claim 9 further comprising using pressure and
temperature differentials in said closed system to circulate said
working fluid in said closed system without using a pump.
11. The method of claim 10 further comprising moving said
circulating working fluid between first and second containers by
exchanging pressures in said containers and by controlling inlet
and outlets of said containers.
12. The method of claim 9, wherein said cryogenic fluid and said
first gas comprise different phases of the cryogenic fluid in an
open system operating on a second thermodynamic cycle.
13. The method of claim 1, wherein one or both of said first and
second energy conversion apparatus comprises a prime mover.
14. The method of claim 1, wherein the working fluid is selected
from the group consisting of sulfur hexafluoride, carbon dioxide,
liquefied natural gas, and a mixture of the above.
15. A method of converting thermal energy comprising: expanding a
portion of a working fluid in a first system operating according to
a first thermodynamic cycle to create a working gas for operating
first energy conversion apparatus; expanding a portion of a
cryogenic fluid in a second system operating according to a second
thermodynamic cycle to create another gas for operating second
energy conversion apparatus, said second system being coupled to
said first system and said expanding comprising transferring heat
from the working gas to said portion of cryogenic fluid to create
said other gas; and transferring additional heat from said working
gas in said first system to said other gas in said second system to
increase the internal energy of said other gas.
16. The method of claim 15, wherein said transferring heat from
said working gas to expand said portion of cryogenic fluid
comprises substantially condensing said working gas.
17. The method of claim 15, wherein said first-mentioned expanding
to create said working gas comprises reducing the pressure and
increasing the temperature of said working fluid in an atmospheric
boiler.
18. The method of claim 15, wherein said transferring additional
heat to said other gas comprises passing said working gas and said
other gas through a common heat exchanger.
19. A method of converting thermal energy, comprising: transferring
heat into a working fluid in a first container to expand a portion
of the working fluid to create a first gas; operating a first prime
mover using said first gas; exhausting said first gas from said
first prime mover into a second container immersed in a cryogenic
fluid in a third container; transferring heat from the exhausted
first gas to said cryogenic fluid to expand a portion of said
cryogenic fluid to create a second gas; operating a second prime
mover utilizing the second gas; and swapping said first and second
containers and repeating said foregoing steps.
20. A system for converting thermal energy, comprising: a cryogenic
fluid reservoir; a condenser for a working fluid, the condenser and
the cryogenic fluid reservoir being in thermal communication for
the transfer of heat to cryogenic fluid in said cryogenic fluid
reservoir to expand a portion of the cryogenic fluid to a first
gas; a boiler for transferring heat to working fluid from said
condenser to expand the working fluid to a second gas, the second
gas operating energy conversion apparatus, and the energy
conversion apparatus exhausting said second gas; a heat exchanger
receiving the first gas and the exhausted second gas for
transferring thermal energy from said exhausted second gas to the
first gas to increase the energy in the first gas; and the first
gas with increased energy operating another energy conversion
apparatus.
21. The system of claim 20, wherein said condenser receives
exhausted second gas from the heat exchanger, said exhausted second
gas comprising said working fluid, and wherein said heat transfer
to the cryogenic fluid condenses said working fluid to a working
liquid, said working liquid comprising said working fluid in said
boiler.
22. The system of claim 21 further comprising first and second
working fluid reservoirs being connected together and to said
condenser and to said boiler by a plurality of lines containing
control valves to enable the control of working fluid through said
lines.
23. The system of claim 20, wherein said heat exchanger comprises
heat conductive pipes through which said gasses pass, the pipes
being in thermal communication for the exchange of thermal
energy.
24. The system of claim 23, wherein said cryogenic reservoir, said
heat exchanger and said other energy conversion apparatus comprise
a first system part that operates according to an open
thermodynamic cycle, and said condenser, said boiler, said heat
exchanger and said first mentioned energy conversion apparatus
comprise a second system part the operates according to a closed
thermodynamic cycle, said system parts being coupled for the
exchange of thermal energy.
25. A method of operating a system that operates on a closed
thermodynamic cycle to circulate fluids through the system without
using a pump, the fluids comprising fluids that expand to a gas and
condense to a liquid upon the transfer and removal of heat, the
method comprising: filling substantially the first tank with cold
liquid and the second tank with hot gas; pressurizing the first
tank with the hot gas from the second tank; flowing cold liquid
into the second tank while expanding the liquid from the first tank
to form a gas; supplying the gas to a prime mover; condensing the
gas from the prime mover to said cold liquid; and repeating said
foregoing steps by swapping said filling, said pressurizing, and
said flowing steps between said first and second tanks, thereby
circulating said fluids through said system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
patent Application No. 60/735,056, filed Nov. 8, 2005, and U.S.
provisional patent Application No. 60/737,682, filed Nov. 17, 2005,
the disclosures of which are hereby incorporated by reference
herein.
TECHNICAL FIELD
[0002] The invention relates generally to methods and apparatus
utilizing cryogenic fluids, and more particularly to methods and
apparatus for utilizing cryogenic fluids for thermal energy
conversion and to operate prime movers.
BACKGROUND OF THE INVENTION
[0003] Systems utilizing cryogenic fluids to operate prime movers
(e.g., engines, turbines, motors, pumps, generators, and
equivalents) to produce various forms of energy have been
investigated as environmentally clean sources of energy. A
cryogenic automobile is a zero-emission vehicle, and one example of
such a clean energy system. It operates on the thermodynamic
potential between the ambient atmosphere and a reservoir of liquid
nitrogen. One way to utilize that potential is through an open
Rankine cycle. Liquid nitrogen is drawn from a tank at the system
pressure, then vaporized and superheated in a two-stage heat
exchange system. The resulting high pressure, near-ambient
temperature gas is injected into a quasi-isothermal expander that
produces the system's motive work. The spent, low-pressure gas is
exhausted back to the atmosphere.
[0004] Although liquid nitrogen powered engines useful for example
in an automobile have been studied in the past, there have been
problems with such engines, including implementing a
quasi-isothermal expander and a frost-free liquid nitrogen heat
exchange system. There are many thermodynamic cycles available for
utilizing the thermal potential of liquid nitrogen. These
thermodynamic cycles range from the Brayton cycle, to two- and even
three-fluid topping cycles, to employing a hydrocarbon-fueled
boiler for superheating beyond atmospheric temperatures. The
easiest system to implement, and the one studied at the University
of Washington, uses an open Rankine cycle. In this system, the
ambient temperature was used to boil the liquid nitrogen and to
raise the pressure in the high pressure side of the engine to on
the order of 30-50 bar. No work was extracted from the cryogenic
fluid in the fluid-to-gas transformation. All work was dissipated
into the ambient around the engine.
[0005] There are several problems with using cryogenic fluids,
including that cryogenic fluids need very effective thermal
insulation, have significant problems with ice condensation within
an engine from the cold temperature fluids used, and are extremely
inefficient for the production of mechanical power from the phase
change of the cryogenic fluid to an expanding gas. The extremely
inefficient production of mechanical power from the phase change of
the cryogenic fluid to an expanding gas is the biggest problem with
existing technology.
[0006] Using phase change in a cryogenic fluid has additional
serious problems. Conventional systems merely dump the heat from
the cold cryogenic fluid at atmospheric ambient temperatures, and
do not fully utilize the thermodynamic possibilities available from
the cryogenic fluid. Some systems use nitrogen gas to preheat the
cryogenic fluid before it enters the heat exchanger, but this only
provides a minor improvement in the overall efficiency of the
energy conversion in the engine.
[0007] Conventional thermal power engines utilizing cryogenic
fluids suffer from a serious limitation, which is low efficiency in
the energy conversion. A need exists for a higher efficiency system
for thermal energy utilization in general, and especially for solar
energy, which does not require expensive equipment, materials, and
maintenance. What is needed is a relatively stable and
non-degradable thermal energy utilization apparatus and method for
long-term operation to utilize thermal energy that is more
efficient and that overcomes the shortcomings described above.
SUMMARY OF THE INVENTION
[0008] The present invention affords a system and method to utilize
ambient thermal energy, including solar energy, geothermal energy,
waste-heat energy, bio-mass combustion energy, and other equivalent
types of energy, and for using cryogenic fluids.
[0009] In a first aspect, the invention affords a method of
converting thermal energy that includes transferring thermal energy
into a cryogenic fluid from a working fluid to expand a portion of
the cryogenic fluid and generate a first gas and condense the
working fluid to a liquid; expanding at least a portion of the
working fluid by transferring thermal energy to the working fluid
to create a second gas; utilizing the second gas to operate an
energy conversion apparatus; and transferring additional thermal
energy to the first gas from second gas exhausted from the energy
conversion apparatus to substantially condense the second gas into
the working fluid, and utilizing the first gas with increased
energy to operate another energy conversion apparatus.
[0010] In another aspect, the invention affords a method of
converting thermal energy by expanding a portion of a working fluid
in a first system that operates according to a first thermodynamic
cycle to generate a first gas for operating energy conversion
apparatus; expanding a portion of a cryogenic fluid in a second
system operating according to another thermodynamic cycle to
generate a second gas for operating other energy conversion
apparatus. The two systems are coupled together, and the method
further involves transferring additional heat from the first gas to
the second gas to increase the energy of the second gas.
[0011] In a further aspect, the energy conversion apparatus
comprises a prime mover, and the inventive method expands a portion
of a working fluid in a first container to create a first gas that
operates a first prime mover. Gas is exhausted from the first prime
mover into a second container immersed in a cryogenic fluid in a
third container to expand a portion of the cryogenic fluid and
create a second gas that operates a second prime mover. The first
and second containers are then swapped as the energy transfer
between the gasses reduces sufficiently to reduce the expansion
processes, and the method is repeated.
[0012] In an additional aspect, the invention affords an apparatus
to utilize a cryogenic fluid to operate a prime mover that includes
at least one cryogenic liquid reservoir, at least one working fluid
liquid condenser, a thermal contact between the cryogenic liquid
reservoir and the working fluid liquid condenser, a first heat
exchanger pipe, a second heat exchanger pipe, a thermal contact
between the first heat exchanger pipe and the second heat exchanger
pipe, a first prime mover coupled to the first heat exchanger pipe,
a second prime mover coupled to the second heat exchanger pipe; an
atmospheric boiler coupled to the second prime mover, at least one
working fluid liquid reservoir coupled to the atmospheric boiler, a
means for moving working fluid from the at least one working fluid
liquid condenser and the at least one working fluid liquid
reservoir, and a plurality of valves, situated so as to isolate at
least one working fluid liquid reservoir, at least one heat
exchanger pipe, at least one working fluid liquid condenser, at
least one prime mover, and at least one cryogenic liquid reservoir
from each other.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a block diagram of a conventional liquid nitrogen
engine;
[0014] FIG. 2 is a block diagram of a dual thermodynamic cycle
cryogenically powered prime mover system in accordance with the
invention, where a cold Rankine cycle engine utilizes the
temperature differential between a cryogenic fluid and the ambient
temperature;
[0015] FIG. 3 illustrates a vapor pressure curve of a working
fluid, sulfur hexafluoride (SF.sub.6), that may be used in the
invention;
[0016] FIG. 4 is a block diagram of the system of FIG. 2 showing a
heat exchanger in more detail and where a conventional feed water
pump is used;
[0017] FIG. 5 is a block diagram of a cryogenic prime mover system,
in accordance with an alternative embodiment of the invention where
a piston-less feed water pump is used in place of a conventional
feed water pump;
[0018] FIG. 6A is a diagrammatic view of an implementation of a
cryogenic prime mover system, in accordance with the invention;
[0019] FIG. 6B is a diagrammatic view showing a first operating
state of the system of FIG. 6A;
[0020] FIG. 6C is a diagrammatic view of a second operating phase
of the cryogenic prime mover system of FIG. 6A;
[0021] FIG. 6D is a diagrammatic view of a third operating phase of
the cryogenic prime mover system of FIG. 6A;
[0022] FIG. 6E is a diagrammatic view of a fourth operating phase
of the cryogenic prime mover system of FIG. 6A;
[0023] FIG. 6F illustrates a cryogenic prime mover system, in
accordance with an alternative embodiment of the invention;
[0024] FIG. 7 is a flowchart of a method of operating a cryogenic
prime mover system, in accordance with the invention;
[0025] FIG. 8 is a flowchart of an alternative method of operating
a cryogenic prime mover system in accordance with the
invention;
[0026] FIG. 9 is a flowchart of a method of operating a cryogenic
prime mover system in accordance with a further embodiment of the
invention; and
[0027] FIG. 10 is a flowchart of a method of operating a cryogenic
prime mover system, in accordance with another embodiment of the
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] Embodiments of the invention can be constructed from
commercially available components. In all of the embodiments
disclosed below, different materials could be used for the chambers
and reservoirs, including but not exclusively including: various
plastics, rubbers, resins, ceramics, and metals. In all of the
embodiments disclosed below, different materials could be used for
the piping, including but not exclusively including: various
plastics, rubbers, resins, ceramics, metals, or other equivalent
manmade materials. The heat exchanger could be a low-temperature
heat exchanger, a mid-temperature heat exchanger, a
high-temperature heat exchanger, or a combination of different
types of heat exchangers.
[0029] FIG. 1 illustrates a block diagram of a conventional open
Rankine cycle liquid nitrogen engine that has been extensively
studied at the University of Washington. As shown, the engine has a
heat source supplying heat 103 to a heat exchanger 102 that is
connected with a pipe 169 to an expander/turbine (e.g., air
turbine, generator, or equivalent) 112, which in turn, is connected
with an output pipe 167 to an economizer 124. The economizer is
connected to an inlet pipe 165 from a liquid nitrogen tank and feed
pump 106. The economizer 124 heats up the liquid nitrogen and
supplies it by an output pipe 104 to the heat exchanger 102. The
engine uses liquid nitrogen stored at a temperature of 77.degree.
K. and a pressure of 1 bar. The nitrogen is pumped, as a liquid, up
to the system working pressure, and this high pressure liquid
nitrogen flows into the economizer 124.
[0030] The economizer 124 is a shell-and-tube type heat exchanger
where the shell-side fluid is the exhaust from the expander. This
has the advantage of providing a frost-free pre-heat to the
incoming liquid nitrogen. Once through the economizer 124, the
vaporized nitrogen enters the heat exchanger, which has a
multi-element, tube-in cross flow configuration. The exterior
fluid, i.e., the ambient atmosphere, is drawn through the core of
the heat exchanger 102 either by the motion of the engine, e.g.,
the vehicle in which it is used, or by a fan, depending on the
operating regime. This heat exchanger 102 must be able to operate
across the normal spectrum of environmental and operating
conditions without suffering the adverse effects of frost
buildup.
[0031] Upon leaving the heat exchanger 102 at 169, the working
fluid is a high pressure, near-ambient temperature gas that is
injected into the expander/turbine 112, which provides all of the
motive work for the system. This expander/turbine can be either a
positive displacement engine or a turbine engine. Following
expansion, the low pressure nitrogen gas exhaust is warm enough to
be used in the economizer 124 to preheat the incoming liquid before
finally being vented to the atmosphere.
[0032] Heat 103 is supplied to the heat exchanger 102, and nitrogen
gas 105 is rejected by the economizer 124. The work output 107 from
this engine is from the expander/turbine (e.g., air turbine,
generator, or equivalent) 112 and the work input 108 to this engine
is used by the tank and feed pump 106. The net work produced by
this engine is the difference of the work output 107 and the work
input to operate the liquid nitrogen tank and feed pump 106.
[0033] The open Rankine cycle operates at critical pressure on the
temperature-entropy diagram. Because pressurization of the working
fluid occurs in the liquid phase of the fluid, the work required is
small in comparison with the available work. One process comprises
the pass through the economizer and heat exchanger. Two other
processes comprise the isothermal and adiabatic modes of expansion,
respectively, that provide the upper and lower limits to the
expander's performance. Another process comprises the liquefaction
stage, and this occurs remotely at an air processing plant.
[0034] In virtually all such known engines, the liquid nitrogen
must be stored in a very well insulated tank having a reservoir
capacity of 50 to 100 liters of liquid nitrogen, and ambient heat
is used to convert the liquid nitrogen to an expanding gaseous
nitrogen to run an air turbine which emits gaseous nitrogen as a
benign exhaust. However, the miles per liter of liquid nitrogen
attainable in a vehicle powered by this engine is typically been on
the order of less than one mile per liter of liquid nitrogen used,
thereby requiring impractically large and cumbersome tanks of
liquid nitrogen. Accordingly, this technology has limited practical
application, and has mainly been only a technological
curiosity.
[0035] As will be described below, the invention provides a system
which has particular utility for more efficiently operating energy
conversion apparatus, such as a prime mover for generating useful
mechanical power, or to do work such as generate chemical energy,
compress gases, or drive generators to produce either AC or DC
electricity. Other embodiments of the invention provide apparatus
or systems that are useful for supplying cryogenic fluids, i.e.,
fluids generated from cryogenic liquefaction of substances such as
nitrogen or oxygen, liquefied natural gas, liquefied hydrocarbon
gases, any mixture of the above, or equivalents.
[0036] More particularly, the invention may employ a modified
closed Rankine cycle engine coupled to a cryogenic fluid in an open
cycle Rankine cycle process to afford a dual thermodynamic cycle
system. The heat needed to boil the cryogenic fluid is supplied by
driving the phase transition of a working fluid, such as SF.sub.6,
CO.sub.2, and others, as will be discussed later, from the gas
phase to the liquid phase. A reservoir of the working fluid is
raised to the ambient temperature (or higher if an external heat
source is utilized). This hot high pressure gas is run through a
prime mover (gas turbine, expander, or equivalent) where the
pressure is lowered and then feed into the condenser where the gas
to liquid phase transition is driven by giving off heat to boil off
the cryogenic fluid.
[0037] A cold engine differs from a conventional hot Rankine (or
steam) engine. In the hot engine, the cold side of the engine is
close to infinite (the heat is dumped into the ambient air
temperature) and the "hot" side of the engine is limited by the
available fuel and the temperature at which that fuel burns. In the
case of the "cold" engine, this is reversed. There is a finite
supply of fuel on the cold side of the engine, and an infinite
amount of heat on the hot side is available from the ambient
environment. The invention utilizes this difference in a novel
system and method to achieve considerable improvements in
efficiency over convention approaches by warming a working fluid
when it is moved from the liquid cold side of the engine to the
liquid hot side of the engine.
[0038] As will be described, the invention also affords a novel
piston-less pump for moving working fluid between hot and cold
sides of the system, without having to rely on a conventional feed
water pump as used in the Rankine cycle engine. The piston-less
feed fluid pump has several advantages over the conventional feed
water pump in a cold engine. It uses the fact that there is an
infinite supply of heat for the operation of the engine. Cold
working fluid can be directly exposed to the hot side of the engine
and brought to working temperature simply by exposing the cold
working fluid to ambient in a heat exchanger, similar to the method
used in the prior art liquid nitrogen powered vehicles. Hot working
fluid gas moves through the prime mover generating power, and is
condensed back to a liquid by boiling the cryogenic fluid. The
gaseous cryogenic fluid is at a high pressure due to the heat
supplied by the phase transformation of the working fluid from gas
to liquid. This high pressure gas is still very cold and can be
used in a heat exchanger to cool the low pressure gaseous working
fluid that is exiting a first prime mover and moving to the low
pressure in a condenser. This will result in warm high pressure
gaseous cryogenic fluid being available for another thermodynamic
cycle system and to work in an expander similar to an open Rankine
cycle. The low pressure gaseous cryogenic fluid is expelled into
the atmosphere from the output of a second prime mover.
[0039] FIG. 2 illustrates a block diagram of a dual thermodynamic
cycle cryogenically fueled prime mover system in accordance with a
first embodiment of the invention. As will be explained, the
invention may comprise a first system or system part operating
according to a first thermodynamic cycle, such as an open Rankine
cycle, coupled to a second system or system part operating on a
second thermodynamic cycle, such as a closed Rankine cycle.
[0040] As shown in FIG. 2, the overall system may comprise a
cryogenic liquid reservoir 202 in thermal contact, i.e., thermal
communication, 204 to a working fluid liquid condenser 206, a
working fluid pump 208, a heat exchanger 209 comprising first and
second half heat exchangers 210 and 212 in thermal contact, i.e.,
thermal communication, 211. Half heat exchanger 210 may be coupled
to the cryogenic liquid reservoir 202; and half heat exchanger 212
may be coupled to the working fluid liquid condenser 206. Condenser
206 may be coupled to the working fluid pump 208, and the pump may
be coupled to a working fluid liquid reservoir 214. The reservoir
214 may be coupled to an atmospheric boiler 228 which is coupled to
a prime mover 222, and that, in turn, is coupled to the half heat
exchanger 212. The atmospheric boiler 228 coupling to prime mover
222 may be through a high pressure gas line 224, and the
atmospheric boiler may further be coupled via a pressure
equalization line 230 to the working fluid liquid reservoir 214. In
a preferred embodiment, the prime mover 216 may be a radial piston
air motor, such as is available from Cooper Power Tools, for
example, or another type of motor or generator. Prime mover 216
which is coupled to the half heat exchanger 210 may produce output
power 218, and prime mover 222 may produce output power 226. Prime
mover 216 may also have an exhaust 220 for exhausting the gas phase
of the cryogenic fluid to the atmosphere.
[0041] The open cycle system part of the overall system shown in
FIG. 2 includes the cryogenic liquid reservoir 202, the half heat
exchanger 210 and the prime mover 216. The closed system part
comprises the working fluid liquid condenser 206, the working fluid
pump 208, the working fluid reservoir 214, the atmospheric boiler
228, the prime mover 222 and the half heat exchanger 212. The
coupling of the two system parts comprises the thermal contact 204
between reservoir 202 and condenser 206, and the thermal contact
211 between the two half heat exchangers 210 and 212.
[0042] As will be explained more fully below, the invention employs
the heat exchange between a cryogenic fluid and a working fluid to
cause phase transitions in the fluids between liquid and gaseous
states, and employs the high pressure gases resulting from such
transitions to drive prime movers to produce work or otherwise
convert the thermal energy to another form. The invention optimizes
this operation by coupling the two different thermodynamic systems
together in a way that substantially improves efficiency by
capturing and using thermal energy that would otherwise be lost in
the two systems. This requires thermal communication, and
preferably physical contact, between containers of the fluids in
the two systems, as by thermal contacts 204 and 211, and as will be
described more fully below.
[0043] The thermal contact 204 between the cryogenic liquid
reservoir 202 and the working fluid liquid condenser 206 may be
achieved by placing the cryogenic liquid reservoir 202 in heat
conductive proximity to (preferably contact with) the working fluid
liquid condenser 206 to enable thermal communication and good
exchange of heat between the reservoir and condenser. The thermal
contact 204 may comprise heat pipes or equivalent heat transporters
to provide thermal communication between the cryogenic liquid
reservoir 202 and the working fluid liquid condenser 206.
Similarly, the thermal contact 211 between the half heat exchanger
210 and the half heat exchanger 212 may be achieved by placing the
half heat exchangers in contact with one another.
[0044] In the embodiment of the invention shown in FIGS. 2 and 4,
the working fluid pump 208 may be a conventional piston pump, for
example, and assists in transporting the working fluid liquid from
the condenser 206 to the reservoir 214. As will be described later,
the invention affords, and other embodiments preferably employ, a
piston-less pumping arrangement instead of a conventional piston
pump for moving the working fluids.
[0045] Suitable fluids and their utility in the invention are
explained in more detail below. In some embodiments of the
invention, one fluid may be used as a working fluid, and a second
fluid may be used as a reservoir fluid. Several possible fluids
that may be utilized for the working fluid, include but are not
limited to sulfur hexafluoride (SF.sub.6), carbon dioxide
(CO.sub.2), liquefied natural gas (LNG), a mixture of the above, or
other non-aqueous fluids that can be liquefied at low pressure at a
temperature above the temperature of liquid nitrogen and at high
pressure and standard temperature, but also exists as a gas at
standard temperature and low pressure. The cryogenic fluid may
comprise liquid nitrogen, for example, which is used to condense a
working fluid, such as SF.sub.6 (or another working fluid, as
described below). The energy needed to drive the gas-to-liquid
phase transformation in the SF.sub.6 working fluid may be supplied
by an equivalent liquid-to-gas phase transition for the liquid
nitrogen. The liquid nitrogen may be maintained well below the
critical point, but still pressurized to several hundred pounds per
square inch (psi). There may be a heat exchange between the cold
nitrogen gas (cryogenic fluid) and the warm SF.sub.6 gas (working
fluid) to improve overall system efficiency, as will be
explained.
[0046] The prime mover 216 being fueled by the cryogenic fluid may
exhaust the gas phase of the cryogenic fluid to the atmosphere at
220. Alternatively, the prime mover 216 may transmit the gas phase
of the cryogenic fluid back into the system, as to a storage
reservoir, for reuse or recycling. Prime mover 216 produces output
power at 218 from the gas expansion of the cryogenic fluid; and
prime mover 222 produces output power at 226 from the gaseous
expansion of working fluid, thereby affording a system that
operates on two thermodynamic cycles. This output power can be
converted to mechanical power, for use in a vehicle such as an
automobile, for example, to chemical energy, or used to compress
gases, and/or to generate electricity. The working fluid in the
engine can be any fluid having a suitable vapor pressure curve, as
shown in FIG. 3. Sulfur hexafluoride is one example of a suitable
working fluid.
[0047] FIG. 3 illustrates a vapor pressure (PV) curve for sulfur
hexafluoride (SF.sub.6) which may be used as a working fluid in the
invention. The vertical axis 302 in FIG. 3 indicates the vapor
pressure of the working fluid SF.sub.6, and horizontal axes
indicate the temperature. The curve 304 indicates the relation
between the vapor pressure of the working fluid SF.sub.6 and the
temperature. Horizontal axis 306 indicates the temperature in
degrees Kelvin (K), and horizontal axis 308 indicates the
temperature in degrees Celsius (C). The working fluid is preferably
a fluid chosen to have a high pressure at the working temperature
(typically ambient) and a much lower pressure at the cryogenic
temperature in the condenser. As mentioned above, both CO.sub.2 and
SF.sub.6 adhere well to these criteria.
[0048] As is well known, the process of evaporation in a closed
chamber will proceed until there are as many molecules returning to
the liquid as there are escaping. At this point the vapor is said
to be saturated, and the pressure of that vapor (usually expressed
in mmHg) is referred to as the saturated vapor pressure. Since the
molecular kinetic energy is greater at higher temperatures, more
molecules can escape the surface and the saturated vapor pressure
is correspondingly higher. If instead the chamber and the liquid
are open to the air, then the vapor pressure is a partial pressure
along with the other constituents of the air. The temperature at
which the vapor pressure is equal to the atmospheric pressure is
called the boiling point. The phase change of a fluid from a liquid
to a vapor (and the reverse process) can be utilized in multiple
ways by the invention, as will be described below.
[0049] Sulfur hexafluoride (SF.sub.6) is a preferred working fluid
because of its pressure at ambient (30-50 bar) and its ability to
be pumped by cryogenic liquid nitrogen in sulfur hexafluoride
(SF.sub.6) recovery systems. The pressure vapor (PV) curve for
carbon dioxide (CO.sub.2) is similar to that of SF.sub.6 and
CO.sub.2 is a good alternative to SF.sub.6. Additionally, the
invention has the advantage of capturing CO.sub.2 in the engine and
removing it from the atmosphere. This is particularly advantageous
if the engine finds substantial use in many applications and
vehicles. Depending on the application and the conditions in which
the invention is used, standard PV curves as shown in FIG. 3 may be
employed to identify other appropriate working fluids.
[0050] FIG. 4 is a block diagram of the system of FIG. 2 showing
more details of the heat exchanger 209 and its relation to other
components of the system, and will be used for describing the
operation of the system.
[0051] As described in connection with FIG. 2, heat exchanger 209
may comprise two half heat exchangers 210 and 212 in thermal
contact with one another. As indicated in FIG. 4, the heat
exchanger 209 may comprise an enclosure housing the two half heat
exchangers 210 and 212 in thermal contact with each other by a
common thermally conducting wall 211 separating the two half heat
exchangers. As mention above, the two heat exchangers 210 and 212
may comprise heat pipes of heat conductive material such as copper,
or some other metal or alloy having good heat transfer
characteristics, preferably joined together by the common wall 211
in such a fashion as to maximize the heat transfer from one pipe to
the other pipe. The heat transfer is a function of the area of the
thermal connection between the two pipes.
[0052] As shown in the figure, half heat exchanger 210 may have a
high pressure cold end coupled to the cryogenic liquid reservoir
202 for receiving cold cryogenic gas from the reservoir 202. This
cold cryogenic gas is produced by adding heat to the cryogenic
liquid from the working fluid in condenser 206 via thermal contact
204 to expand the cryogenic liquid to a gas. Half heat exchanger
also has a high pressure hot end coupled to the prime mover 216 for
providing high pressure hot cryogenic gas to the prime mover. The
cryogenic gas flowing through half heat exchanger 210 receives
additional heat via thermal contact 211 from the hot working fluid
gas flowing in half heat exchanger 212 to increase its internal
thermal energy. This additional thermal energy substantially
increases efficiency of the system by increasing the energy in the
hot gas flowing to prime mover 216.
[0053] Half heat exchanger 212 has a low pressure hot end coupled
to the prime mover 222 for receiving the hot exhaust working fluid
gas from the prime mover, which is exhausted at low pressure from
the prime mover. As the hot exhaust gas passes through the half
heat exchanger 212, it is chilled by the transfer of heat to the
expanded cryogenic fluid gas in half heat exchanger 210, and exits
the half heat exchanger 212 at a low pressure cold end coupled to
the working fluid liquid condenser 206. The chilled working fluid
gas enters the condenser 206 where it is further chilled and
condensed to a liquid by the heat transfer via thermal contact 204
to the cryogenic liquid in reservoir 202, which causes the
cryogenic liquid to undergo a liquid-to-gas phase transition, as
described above.
[0054] Advantageously, in accordance with the invention, the hot
working fluid gas from prime mover 222 that enters and flows
through half heat exchanger 212 heats the cryogenic gas that flows
through half heat exchanger 210 to prime mover 216 to further
increase the internal energy of the cryogenic gas, as explained.
The cryogenic gas exiting the high pressure hot end of the heat
exchanger 210 to prime mover 216 will be heated to a temperature
closer to the temperature of the working fluid entering heat
exchanger 212 from prime mover 222, thereby providing more to the
prime mover 216 and substantially increasing its output power. In
fact, the increased temperature differential over ambient resulting
from heating of the cryogenic gas by hot working fluid gas in the
heat exchanger 209 results in an increase in work output of the
order of three to four times over conventional open Rankine cycle
systems. Moreover, by the time the working fluid gas from prime
mover 222 exits the cold end of half heat exchanger 212, it will be
much nearer in temperature to the cryogenic fluid than when it
entered the heat exchanger due to the heat transfer to the
cryogenic liquid flowing through half heat exchanger 210, thereby
facilitating the gas-to-liquid phase transition in the condenser.
This heat exchange between the two fluids improves system
efficiency.
[0055] The working fluid may be pumped by a conventional working
fluid pump from the condenser to the working fluid liquid
reservoir, where the temperature of the working fluid liquid will
be near but somewhat less than ambient and its pressure will be of
the order of 40-50 bar, when the working fluid is sulfur
hexafluoride. From the reservoir 214, the working fluid flows to
the atmospheric boiler 228 where it receives thermal energy and
undergoes a phase change from a liquid to a vapor and forms the
high pressure hot working fluid gas that drives the prime mover
222. As noted, this high pressure hot gas is exhausted from the
prime mover to the heat exchanger 212. The atmospheric boiler 228
may be coupled back to the reservoir 214 by a pressure equalization
line 230, as shown.
[0056] FIG. 5 illustrates a block diagram of an alternative
embodiment of a cryogenic prime mover system in accordance with of
the invention. As shown in FIG. 5, this alternative embodiment may
be similar to the system of FIGS. 2 and 4, comprising a cryogenic
liquid reservoir 202, a thermal contact 204 to a working fluid
liquid condenser 206, a working fluid pump 208, a heat exchanger
210 coupled to the cryogenic liquid reservoir 202, and a heat
exchanger 212 coupled to the working fluid liquid condenser 206.
However, the embodiment of FIG. 5 differs in several significant
respects from those embodiments.
[0057] In addition to a first working fluid liquid reservoir 214,
the system of FIG. 5 may also comprise a second working fluid
liquid reservoir 215 coupled (as at 217) to the first working fluid
reservoir 214, and the two reservoirs may be coupled to the
condenser 206. Additionally, the working fluid pump 208 of FIG. 2
and 4 which was used to circulate working fluid may be eliminated.
Instead, as will be described below in connection with FIGS. 6A-E,
the reservoirs 214 and 215 and their interconnections in the system
of FIG. 5 afford a piston-less pumping operation that moves the
working fluid in the system without the necessity of a conventional
pump. Additionally, the system of FIG. 5 may comprise a pump 604
and a hot storage collector 602 coupled together with the
atmospheric boiler 228, as shown. The pump 604 and hot storage
collector 602 are advantageous in allowing additional heat to be
transferred to the atmospheric boiler to raise its temperature
above ambient, by pumping a transfer liquid, such as oil or liquid
sodium, from the boiler through the hot storage collector 602. Hot
storage collector 602 may comprise, for instance, cooling fins as
in a radiator that operates at ambient temperature. This allows
heat to be captured and added to the boiler to improve its
efficiency and to increase the thermal energy in the working gas
flowing to prime mover 222.
[0058] As also shown in the figure, the first and second working
fluid liquid reservoirs 214 and 215 may both be coupled to
atmospheric boiler 228. The atmospheric boiler may couple back to
the first and second working fluid liquid reservoirs 214 and 215
via a pressure equalization line 230, and the boiler may supply
high pressure hot gaseous working fluid to prime mover 222 via high
pressure gas line 224. The two working fluid liquid reservoirs may
also be connected together and to the boiler by a line 217.
[0059] As explained above, the working fluid from the reservoirs
214, 215 undergoes a phase change from a liquid to a vapor upon the
application of thermal energy in atmospheric boiler 228. This vapor
is at high pressure and may be used to drive the prime mover 222 to
produce work 226, as explained above, and the exhaust from the
prime mover may be supplied to the half heat exchanger 212.
[0060] FIGS. 6A-6E are more detailed diagrammatic views of a dual
thermodynamic cycle cryogenically fueled prime mover system in
accordance with the invention as shown in FIG. 5, and illustrate
various phases (states) of the system and its control as the system
progresses through an operating cycle. The figures also illustrate
the piston-less pumping aspect of the invention.
[0061] As described, the working fluid portion of the system may
comprise a closed loop system in which the working fluid is
recycled and reused as the system, whereas the cryogenic portion of
the system is an open system that does not reuse cryogenic fluid,
but exhausts it to the atmosphere from a prime mover
(motor/generator). These two systems operate according to different
thermodynamic cycles that may comprise, respectively a closed
Rankine cycle and an open Rankine cycle. The arrangement of the
system components and the control by the valves of the pressure and
flow through the working fluid reservoirs (tanks 1 and 2) affords a
piston-less pump arrangement that circulates fluid through the
closed cycle working fluid portion of the system without the
necessity of a conventional pump.
[0062] Referring to FIG. 6A, cryogenic liquid reservoir 202 may be
a container of liquid nitrogen (LN.sub.2), for example, in thermal
communication with the working fluid liquid condenser 206 for
SF.sub.6 or CO.sub.2, for example, SF.sub.6 being shown in the
figure. The thermal communication may be effected by the thermal
contact 204 between the cryogenic liquid reservoir 202 and the
working fluid liquid condenser 206. The first and second working
fluid liquid reservoirs 214 and 215 may comprise two tanks
connected to the condenser 206 by valves V1 and V2, and connected
together by a valve V3. The atmospheric boiler 228 may comprise an
evaporator which receives heat 606, as from the atmosphere or
another heat source to convert the working liquid to a gas, and the
two reservoir tanks may also be connected to the evaporator by a
line 232 having control valves V4 and V5, and by pressure
equalization lines 234 and 236 (corresponding to line 230 of FIGS.
4-5) respectively having control valves V6 and V7.
[0063] A prime mover (e.g., motor/generator) 216 may be coupled to
the cryogenic liquid reservoir 202 through an evaporator 203, and a
prime mover (e.g., motor/generator) 222 may be coupled to the
working fluid liquid condenser 206 and to the atmospheric boiler
(evaporator) 228 via a line 224 and control valve V8. The prime
mover 216 has an exit to atmosphere 220 for releasing gas from the
cryogenic fluid produced by evaporator 203.
[0064] Valves V1 and V2 control the flow of working fluid into
working fluid liquid reservoirs (tanks) 214 and 215, respectively.
Valve V3 controls the pressure equalization and the flow of working
fluid between working fluid liquid reservoirs 214 and 215. Valves
V4 and V5 respectively control the flow of working fluid from
working fluid liquid reservoirs 214 and 215 into the evaporator
(atmospheric boiler) 228. Valves V6 and V7 may control the
equalization of pressure in the working fluid liquid reservoirs 214
and 215, respectively, relative to the evaporator (atmospheric
boiler). Valve V8 controls the flow of working fluid gas between
the motor/generator (prime mover) 222.
[0065] FIG. 6B is a simplified view of the cryogenic prime mover
system of FIG. 6A showing the system in a first operating phase
(state). FIG. 6B shows the system with all the valves in the closed
position. Reservoir 215 (i.e., tank 2) is substantially full of
cold working fluid liquid, and reservoir 214 (i.e., tank 1) is more
or less empty of working liquid but contains high pressure warm
working gas. Valves V1 and V2 are shut-off to stop the flow of
working fluid into the working fluid liquid reservoirs 214 and 215,
respectively. Valve V3 is shut-off to stop the flow of working
fluid between the working fluid liquid reservoirs and to maintain
the separate pressures in each reservoir. Valves V4 and V5 are
shut-off to stop the flow of working fluid from the working fluid
liquid reservoirs into the evaporator (atmospheric boiler) 228, and
valves V6 and V7 are shut-off to stop the equalization of pressure
in the working fluid liquid reservoirs relative to the evaporator
(atmospheric boiler) 228. Valve V8 is shut-off to stop the flow of
working fluid gas to the motor/generator (prime mover) 222. The
system is shown in a quiescent state in FIG. 6B.
[0066] FIG. 6C illustrates a next second phase of the system from
the state shown in FIG. 6B in which valves V1, V5, V7 and V8 are
opened. Working fluid liquid reservoir 215 (tank 2) is
substantially full of cold working fluid. The working fluid from
tank 2 may feed the evaporator 228, which expands the working fluid
to supply hot gas to the generator 222. The hot gas from the
generator 222 is condensed and liquefied in the condenser 206
(which is in thermal contact 204 with the cryogenic liquid
reservoir 202, as shown in FIG. 6A), and stored as cold working
fluid liquid in reservoir 214 (tank 1). Not shown in the figure,
there is preferably a heat exchanger in the line between tanks 1
and 2 and the evaporator 228 that uses the hot gas exhausted from
the generator 222 to the condenser to heat the warm working fluid
flowing to the evaporator. This increases the energy in the working
fluid to the evaporator, and removes heat from the exhaust gas to
the condenser to increase system efficiency.
[0067] Valve V1 may be open to allow working fluid from condenser
206 to flow into working fluid reservoir 214, and V2 may be
shut-off to stop the flow of working fluid into working fluid
reservoir 215. Valve V3 is shut-off to stop the flow of working
fluid between working fluid reservoirs 214 and 215 and to maintain
the reservoir pressures. Valve V4 is shut-off, and V5 is open to
permit the flow of working fluid from working fluid reservoir 215
into evaporator 228. Valve V6 is shut-off and V7 is open to permit
the equalization of pressure in the working fluid liquid reservoir
215 relative to the evaporator 228. Finally, valve V8 is open to
permit the flow of hot working fluid gas from the evaporator to the
motor/generator 222.
[0068] FIG. 6D illustrates a next third phase of the system of FIG.
6A, in which working fluid reservoir 214 is substantially full of
cold working liquid, and working fluid reservoir 215 is
substantially empty of liquid but contains hot gas which filled the
reservoir from reservoir 214 when valve V3 was opened. With valve
V3 open, the pressure is equalized between reservoirs 214 and 215.
When the pressure is equalized, valve V3 may be closed and the
system will be ready to reverse the cycle. Valves V1 and V2 may be
shut-off to stop the flow of working fluid into working fluid
liquid reservoirs 214 and 215, respectively. Valves V4 and V5 may
be shut-off to control the flow of working fluid from working fluid
liquid reservoirs 214 and 215 into the evaporator 228. Valves V6
and V7 are shut-off to stop equalization of the pressure in the
working fluid liquid reservoirs 214 and 215 relative to the
evaporator 228. Valve V8 is shut-off to stop the flow of working
fluid gas to the motor/generator (prime mover) 222.
[0069] FIG. 6E illustrates a fourth phase of the system that is
similar to the state shown in FIG. 6A, where the system flow is
reversed from the state of FIG. 6D. Working fluid reservoir 214
(tank 1) is substantially full of warm working liquid (warmed by
the hot gas flow from tank 2 in the phase shown in FIG. 6D) and may
be used to feed the evaporator 228 and power the generator 222.
Working fluid reservoir 215 (tank 2) is substantially empty of
liquid, but contains cold working fluid from the condenser 206.
Valve V1 is shut-off and V2 is open to control, respectively, the
flows of working fluid into working fluid reservoirs 214 and 215.
Valve V3 is shut-off to stop the flow of working fluid between
working fluid reservoirs 214 and 215. Valve V4 is open and V5 is
shut-off to control the flow of working fluid from working fluid
liquid reservoirs 214 and 215 into evaporator 228. Valve V6 is open
for the equalization of pressure in the working fluid reservoir 214
relative to evaporator 228 and to enable the working fluid to flow
from reservoir 214 to the evaporator, and valve V7 is closed. Valve
V8 is open to permit the flow of working fluid gas to the
motor/generator 222.
[0070] The working liquid in working fluid reservoir 214 (tank 1)
is warm because of the flow of hot gas from reservoir 215 and
because the liquid is heated to the ambient atmospheric temperature
in the tank. As described above, there is preferably a heat
exchanger in the line between the working fluid reservoir and the
evaporator that uses the hot exhaust gas from the generator 222 to
preheat the working fluid flowing to the evaporator. Moreover, in
an alternative embodiment (not illustrated) the cold fluid from
working fluid reservoirs may be used in either condenser 206 assist
in condensing the gas from the generator, or may be used in another
system having tanks 3 and 4 arranged similar to that shown and run
another cycle and extract additional energy from the working
fluid.
[0071] As will be appreciated from the foregoing description of the
operating states of the system as shown in FIGS. 6A-E, the movement
of working fluid between the reservoir tanks 1 and 2 (214 and 215)
and its circulation through the system, is controlled by the
pressure and temperature differentials between the two working
fluid reservoirs and between other system components, and by the
positions of the various valves in the interconnecting lines. By
appropriate control of the valves, the system can be cycled through
its various states and the working fluid can be circulated through
the system by using these pressure differentials without the
necessity of a conventional pump. The arrangement of the system
components and valves effectively affords a piston-less
(non-moving) pump that effects transport of fluids based on the
pressure and temperature differentials, thereby avoiding the
necessity of a conventional pump, such as a feed water pump used in
conventional Rankine cycle engines. As will be appreciated from the
foregoing, this piston-less pump has more general applicability to
other types of systems employing fluids that expand with heat and
condense with cold to produce varying pressures differentials as
the system progress through an operating cycle.
[0072] FIG. 6F illustrates an open loop cryogenic prime mover
system in accordance with an alternative embodiment of the
invention. FIG. 6F illustrates a simpler embodiment of that shown
in FIG. 6A-6E. This system uses a single container or tank of hot
working fluid 214 which is raised to its boiling point for a given
input pressure to a motor/generator 222 (prime mover) by a heating
tape 608 surrounding the container. The working fluid is expanded
in the motor/generator, and then re-condensed in a second container
or tank 215 disposed in an insulated dewar 614, pressure sealed at
612, that contains a cryogenic fluid such as liquid nitrogen,
LN.sub.2. As the liquid nitrogen absorbs heat from the working
fluid, it vaporizes into a hot gas, and pressurizes the interior of
the sealed dewar. The pressurized liquid nitrogen may be supplied
through a pressure regulator 616 to another motor/generator (prime
mover) 216, and exhausted at 220 to the atmosphere. Power is
generated both by the movement of the working fluid from tank 214
through motor/generator 222 to tank 215, as well as by the movement
of warm gaseous cryogenic fluid through prime mover 216 as it is
vented at 220 to the atmosphere.
[0073] At the start of the cycle, the tank 214 may be substantially
full of working liquid (i.e., working fluid), such as the
previously mentioned fluids SF.sub.6 or CO.sub.2. This working
liquid may be transitioned (changed) to the gas phase using heat
added by the heating tape 608 to create a high-pressure working
gas. The working gas flows through the generator 222 to the
low-pressure side of the generator and into container 215, where it
is re-liquefied in the container. The phase transition from
gas-to-liquid is exothermic, and the energy to drive this reaction
is provided by the liquid-to-gas transformation occurring in the
LN.sub.2 pressure vessel 202 comprising the insulated dewar
614.
[0074] As the cycle proceeds, work is done in the two generators
222 and 216 as the high-pressure working fluid in the tank 214
transitions to the gas phase and moves through the motor/generator
and into the tank 215. Work is also done by the pressurized gas
created in the LN.sub.2 pressure vessel 202 as it is vented through
the motor/generator 216 to the atmosphere.
[0075] When the cycle is completed, substantially all of the liquid
working fluid may have moved from working fluid tank 214 into
working fluid tank 215. The tanks 214 and 215 may then be
disconnected from the system and physically exchanged or switched
places so that the original right-most tank (in the figure) 215
becomes the new left-most heated tank 214, once again full of the
working fluid, and the original left-most tank 214 becomes the new
right-most tank 215 ready to be chilled to condense the working gas
to a liquid state.
[0076] As will be appreciated, the embodiment of FIG. 6F is a
manual system, rather than an automatic system such as FIGS. 6A-E,
since following one cycle of operation, the system must be "reset"
before a second cycle may be commenced. Moreover, while the working
fluid portion of the system is a closed system, since working fluid
may be recycled and reused in a subsequent cycle, the cryogenic
portion of the system is an open system since liquid nitrogen is
not recycled, but rather is exhausted to the atmosphere. Therefore,
the liquid nitrogen dewar will have to be recharged
periodically.
[0077] The invention can be used to generate electrical energy,
either for fixed locations, e.g., for residential or business use,
or for moving vehicles, e.g., for automobiles, trucks, etc.
Generating electrical energy in large quantities for an electrical
power grid using conventional power generation approaches is not
trivial, especially for AC electricity power grids, since large
amounts of AC electrical energy needed by an electricity power grid
cannot be readily stored. Therefore the energy taken from an
electrical power supply grid must be equal to the energy being
delivered.
[0078] Cryogenic fluid reservoir systems in accordance with the
invention solve this problem by storing electrical energy as
potential energy in cryogenic fluids. Systems of the invention may
generate cryogenic fluids at times of surplus energy on an
electrical supply grid, typically at night, store the energy as
potential energy, and then release the potential energy through an
electrical generator at times of high demand. Use of electric
generator turbines allows direct energy conversion to AC electrical
power. Electrical DC to AC conversion as used in many conventional
alternative energy systems is not required, thereby significantly
reducing the complexity, reliability problems, and cost of
construction and maintenance of energy generation plants, as
compared to conventional DC electricity supply systems.
[0079] FIG. 7 is a flowchart of a method of converting thermal
energy to another useful form of energy, in accordance with the
invention. The method begins at 702. At 704, thermal energy is
transferred into a cryogenic fluid from a working fluid to vaporize
a portion of the cryogenic fluid and generate a first working fluid
gas. At 706, the first gas may be used to operate a first prime
mover to convert the energy of the first gas to a different form.
At 708, at least a portion of the working fluid may be vaporized to
create a second working fluid gas. At 710, the second gas may be
utilized to operate a second prime mover. At 712, the second gas
may be routed through a heat exchanger to substantially condense
the second gas back into working fluid liquid. The method ends at
operation 714.
[0080] FIG. 8 illustrates a flowchart of an alternative method of
converting thermal energy to another form of energy that is
substantially similar to the method of FIG. 7. Steps 802-806 and
812-817 of FIG. 8 are substantially the same as steps 702-714 of
FIG. 7. The difference in the methods of FIGS. 7 and 8 is that the
method of FIG. 8 includes, following the step at 806 (where the
first gas is used to operate a prime mover), the additional step at
808 of moving a portion of the working fluid to a reservoir. The
remainder of the steps of the method may be the same as shown in
FIG. 7.
[0081] FIG. 9 illustrates a flowchart of another method of
generating energy in accordance with the invention. The method
begins at 902. At 904, a first portion of a working fluid is stored
in a first working fluid reservoir. At 906, a second portion of the
working fluid is stored in a second working fluid reservoir. At
908, thermal energy is transferred into a cryogenic fluid, for
instance from the first portion of working fluid, to vaporize a
portion of the cryogenic fluid to generate a first gas. At 910, the
first gas may be used to operate a first prime mover. Next, at 912,
the first portion of the working fluid may be separated from the
second portion of the working fluid, and at 914 the first portion
of the working fluid may be vaporized to generate a second gas. At
916, the second gas may be utilized to operate a second prime
mover. This prime mover can be used to convert the energy in the
second gas to another form of energy, as, for example, to generate
mechanical power, electrical power, compress gases, or create
chemical energy. At 918, the second gas may be routed through a
heat exchanger to substantially condense the second gas into the
first portion of the working fluid. Next, at 920, the preceding
three operations at 914, 916 and 918 may be repeated using the
second portion of the working fluid rather than the first portion,
after swapping the roles of the first and second working fluid
reservoirs. The method ends at 922.
[0082] FIG. 10 is a flowchart of a method of generating electricity
in accordance with the invention. The method begins at 1002, and at
1004, thermal energy is transferred into a cryogenic fluid from a
working fluid to vaporize a portion of the cryogenic fluid and
generate a first gas. At 1006, the first gas may be utilized to
operate a first prime mover that may include a first generator. A
1008, at least a portion of the working fluid may be vaporized to
create a second gas, which may be included, as indicated at 1010,
to operate a second prime mover that may include a second
generator. At 1012, the second gas may be routed through a heat
exchanger to substantially condense the second gas into the working
fluid. The method ends at 1014.
[0083] As will be appreciated from the foregoing, while the
invention has been described with reference to preferred
embodiments, various changes in these embodiments may be made
without departing from the spirit and principles of the invention,
the scope of which is defined in the appended claims.
* * * * *