US3667215A - Heat engines - Google Patents

Heat engines Download PDF

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Publication number
US3667215A
US3667215A US878817A US3667215DA US3667215A US 3667215 A US3667215 A US 3667215A US 878817 A US878817 A US 878817A US 3667215D A US3667215D A US 3667215DA US 3667215 A US3667215 A US 3667215A
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heat
medium
expansion
substantially constant
cycle
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Venkataramanayya K Rao
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Atomic Energy of Canada Ltd AECL
Nordion Inc
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Atomic Energy of Canada Ltd AECL
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K27/00—Plants for converting heat or fluid energy into mechanical energy, not otherwise provided for
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02C—GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS
    • F02C1/00—Gas-turbine plants characterised by the use of hot gases or unheated pressurised gases, as the working fluid
    • F02C1/04—Gas-turbine plants characterised by the use of hot gases or unheated pressurised gases, as the working fluid the working fluid being heated indirectly
    • F02C1/10—Closed cycles
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02G—HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS; USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR
    • F02G2242/00—Ericsson-type engines having open regenerative cycles controlled by valves

Definitions

  • HEAT ENGINES Inventor: Venkataramanayya K. Rao', Bangalore, [561 References cited lnda UNlTED STATES PATENTS [73] Assignee: Atomic Energy of Canada Limited Commerits. Ottawa Ontario, 2,869,830 l/ I959 Cox ..60/59 T Canada Primary Examiner-Martin P. Schwadron [22] Filed: Nov. 21, 1969 Assistant Examiner-Allen M. Ostrager [21 1 pp No: 878,817 Attomey-Cushman.
  • FIG. 4A FIG. 4B
  • FIG.4C PRIOR ART PRIOR ART PRIOR ART PRIOR ART PATENTEDJUH 6 m2 3, 667, 215
  • This invention relates to a method and apparatus for the I thermal to mechanical conversion of energy.
  • the invention has particular, but not exclusive application, in the ufilization of heat which is not at a relatively high temperature.
  • the present invention resulted from a need to provide a small heat engine to convert thermal energy, derived from decay of a radioisotope source, into mechanical and electrical energy.
  • thermal energy derived from decay of a radioisotope source
  • Such a requirement was stimulated in the expectation that certain navigational aids, i.e. lamps, fog detectors, fog signals, radio beacons etc., could be left unattended for long periods in remote locations.
  • the minimum efficiency of conversion be set at 20 percent, that the power output for one embodiment be of the order of 600 watts and that the maximum temperature of the available thermal energy be about 600 C.
  • the method comprises the steps: compressing a gaseous medium in a first space having a lower mean temperature and pressure by a compression ratio r," adding heat at substantially constant pressure to the compressed medium, adding further heat from a source to the compressed medium at substantially constant volume, expanding the said medium into a second space having a high mean temperature and pressure by an expansion ratio R, where R is greater than r, extracting an amount of heat from the expanded gas at substantially constant pressure and substantially equal to the first mentioned added heat, cooling said medium at substantially constant pressure, utilizing the work done by the medium during expansion to provide the work required for the compression step and a mechanical output, and, cycling repeating all the foregoing steps.
  • the invention comprises: compression means for compressing the working medium by a ratio of r, heat exchanger output means for adding heat at constant pressure to the compressed medium, means for adding further heat at constant volume, expansion means a second portion of the energy converted in the expansion means to a mechanical output, and, means for respectively cycling all the foregoing means in succession.
  • FIG. 1 (prior art) is a diagram of a simple gas turbine power plant and the computed thermal efficiency as a function of pressure ratio.
  • FIG. 2 (prior art) is a similar diagram to the preceding one, differing from it by the incorporation of reheat and regeneration into the plant.
  • FIG. 3 shows the basic components of the Rankine cycle.
  • FIGS. 4A, 4B, 4C are graphs of Temperature-Entropy characteristics for the Rankine cycle using Wet, Dry and Ideal Expansion, respectively.
  • FIG. 5 is a diagram of a heat engine, according to the present invention, on its upward stroke.
  • FIG. 6 is similar to FIG. 5, but wherein engine is on its downward stroke.
  • FIG. 7 is a Pressure-Volume diagram of the ideal thermodynamic cycle of the heat according to the present invention.
  • FIGS. 8 and 9 are graphs depicting the computed performance characteristics of the ideal thermodynamic cycle as in FIG. 7 with carbon dioxide and air, respectively, as working media.
  • Direct Conversion For use with radioisotope sources, only two methods of direct conversion need be considered(a) Thermoelectric and (b) Thermionic conversion systems. Both the systems are in service and under development in great variety by a number of civil and military organizations mainly in the United States. The most recent and comprehensive source of reference of these endeavors is the Proceedings of the 1967 Intersociety Conference on Energy Conversion Engineering. Numerous power generators built under the SNAP program-Systems for Nuclear Auxiliary Poweruse one or the other of these two methods of energy conversion. The present state of the art of these devices is summed up in the table below.
  • the indirect conversion systems which can also be called dynamic conversion systems, make use of a heat engine to convert thermal power to mechanical, which is later converted easily to electric power.
  • thermodynamic cycle on which the heat engine operates.
  • the working medium is a gas which does not change phase during the cycle. Any gas may be used as the working medium as the performance of the system is, theoretically, independent of the properties of the working medium. There are no problems of degradation of the working medium due to high temperatures or irradiation.
  • the thermal efficiency of the Brayton Cycle depends on the maximum cycle temperature and is extremely sensitive to component performance.
  • the modifications include regeneration and reheat.
  • FIG. 1 represents the performance of what is termed the CBTX cycle.
  • a schematic layout of the system working on the CBTX cycle is shown therein.
  • the working medium is compressed in the compressor C and heated in the heater B using the radioisotope source after passing through the regenerator X.
  • the gas then expands through the turbine Twhich exhausts through the regenerator X.
  • An open cycle is shown on the assumption that the working medium is air.
  • the power available on the turbine shaft in excess of the power requirements of the compressor is the useful power.
  • the efiiciency can be improved somewhat by using a more complicated system as depicted in FIG. 2 which is designated as the CBTRTX cycle.
  • This cycle incorporates both reheat and regeneration.
  • the working medium is re-heated back to the maximum cycle temperature after a partial expansion through the turbine T and expanded again to the lowest possible pressure through the turbine T As is evident, this is a more complicated arrangement than the previous one.
  • the Brayton Cycle can hence be ruled out for the present application especially in view of the merits of the other cycles to be discussed next.
  • the Rankine Cycle is inherently a very eflicient cycle because heat addition and heat rejection take place mainly at the highest and at the lowest cycle temperatures respectively.
  • the basic components of a Rankine system are the turbine, the feed pump, the heat source and the heat sink or condenser and are shown in FIG. 3.
  • the main feature of this system is that the working medium undergoes a phase change during the cycle.
  • Balje has provided contours of constant efficiency on N,D, plots. For optimum performance, then, a turbine must operate at fixed values of N, and D,. Consequently N, X D, constant for that point, so that (N-D) (HQ constant. This shows that the turbine tip speed is directly proportional to the square root of the enthalpy drop through the turbine.
  • the critical pressure 2. The molecular weight, and
  • the expansion through the turbine is, ideally, isentropic.
  • the source and sink temperatures and the mean pressure level in the system are assumed fixed.
  • the speed of the turbine therefore decreases with an increase in the molecular weight of the fluid. Since a definite volume flow is to be maintained for a given output, the components of the turbine can be made larger and more efiicient in low power units.
  • the other property of the fluid of significance in turbine design is the slope of the saturated vapor line on Temperature- Entropy coordinates. If this slope is negative, as is the case with water and liquid metals, the vapor becomes "wet after expansion through the turbine nozzle giving rise to erosion problems. If the slope is positive as with many organic fluids, the vapor becomes superheated after expansion and needs to be de-superheated before it can be condensed. The ideal situation, of course, is to have an infinite slope for the line.
  • the Stirling Cycle is a regenerative cycle and, theoretically, achieves the highest possible thermal efficiency between a given set of source and sink temperatures.
  • the thermal efficiency of the Stirling Cycle is the same as that of the Carnot Cycle.
  • the evolution of a mechanical device to operate on this thermodynamic cycle has needed very ingenious and refined mechanical design.
  • the Philips engine is a very elaborate mechanical arrangement with two coaxial pistons reciprocating in one cylinder with no lubrication.
  • the working medium is either Helium or Hydrogen gas at a mean pressure of about 1 1O atmospheres. These high mean pressures are required to achieve a reasonably high specific output (output/weight) from the engine and naturally impose problems of the dynamic seal between the piston rod and the cylinder.
  • the maximum source temperature is at present limited to 700 C. It is contemplated that this will be increased to 800 C. and the mean gas pressure to 220 atmospheres with the use of better creep resisting materials in the near future.
  • thermodynamic cycle A simple mechanical device intended to work on a new thermodynamic cycle of high efficiency which may be adapted to a radioisotope source will now be presented. Though this thermodynamic cycle is not as efficient as the Stirling Cycle, it is more efiicient than most conventional cycles. The simplicity of the corresponding mechanical device might make the concept of this heat engine worth pursuing further.
  • the engine consists of a mechanism containing a cylinder and reciprocating piston in which both sides of the piston are utilized to subject a working medium to various thermodynamic processes. Some of these processes occur simultaneously above and below the piston.
  • a heat source, a heat sink and a regenerator are the other components of the engine. Valves are located in the passages connecting these components with each other to regulate the flow of the working medium among them.
  • FIG. 5 shows the piston in its upward stroke. During this stroke, the following events take place:
  • Valve V in the space above the-piston: Valve V is closed. Valve V, is open. Hot gas is displaced into the Cooler (Heat sink) through the Regenerator.
  • Valve V is open. Valve V is closed. Cool gas from the Cooler is sucked in.
  • FIG. 6 shows the piston in its downward stroke. During this stroke, the following events occur:
  • Valve V is open. V is closed, The gas to which heat energy has been added in the Heater (Heat source) increasing its pressure now expands.
  • Valve V in the space below the piston: Valve V is closed. Valve V is open. The cool gas sucked in during the previous stroke is compressed and displaced into the Heater through the Regenerator.
  • the intended processes for the working medium can now be traced as follows: Starting at its lowest temperature at the exit of the Cooler, the working medium is sucked into the space below the piston. It is then compressed (adiabatically) and admitted to the Heater through the Regenerator. In the Regenerator, the working medium picks up some heat energy (at constant pressure) and is then further heated (at constant volume) in the Heater to its maximum temperature and pres sure in the cycle. The time required for the entire upward stroke of the piston is available for heat transfer to the working medium in the Heater. This process is intended to take place at constant volume by keeping the valves V and V, shut. The working medium is now made to expand (adiabatically) in the space above the piston such that its pressure falls down to the lowest pressure in the cycle. This is achieved by providing a higher volume ratio during expansion than that during compression. These ratios can be adjusted to the appropriate values by choosing the correct piston rod diameter.
  • The. working medium is then displaced into the. Cooler through the Regenerator which picks up a part of the heat energy (at constant pressure) remaining in the working medium.
  • the working medium is finally cooled to its lowest temperature in the cycle in the Cooler (at constant pressure). This completes the thermodynamic cycle of the working medium.
  • thermodynamic cycle for the working medium is shown in FIG. 7. The following points should be noted in connection with this engine.
  • the expansion ratio is higher than the compression ratio. This results in the utilization of the toe of the indicator diagram that is nonnally lost in conventional engines where the compression and expansion ratios are nearly equal. It is possible to achieve this because the compression and the expansion processes take place on opposite sides of the piston in the present engine.
  • the process of regeneration at the end of the compression process utilizes some of the energy in the gases that have undergone expansion. This raises the mean temperature at which heat is added and lowers the mean temperature at which heat is rejected in the cycle.
  • thermodynamic cycle A detailed analysis of this thermodynamic cycle has been carried out using a digital computer.
  • the maximum cycle temperature was fixed at 600 C. l,570 R.) as specified.
  • the following gases were investigated in turn as to their performance as working media in the engine: Air, Nitrogen, Carbon Dioxide, Hydrogen Helium, Argon, Sulphur Dioxide. Air and Carbon Dioxide result in a better performance than the rest with Carbon Dioxide giving the best overall performance.
  • FIGS. 8 and 9 The results obtained on the computer with Carbon Dioxide and Air as working media are plotted in FIGS. 8 and 9 respectively.
  • the process of regeneration can be effected only as long as the temperature at the end of the compression process is lower than the temperature at the end of the expansion process.
  • Curves A and B in FIGS. 8 and 9 therefore merge with each other at some value of the compression ratio.
  • Curve C in FIGS. 8 and 9 shows the specific output of the engine the output per unit rate of mass flow of the working medium through the engine.
  • a practical limitation on the minimum size of the engine may be imposed by the speed being limited by the rate of heat transfer in the regenerator. Also, the minimum mean pressure may be determined by heat transfer.
  • Appendix A An analytical expression for the thermal efficiency of the ideal cycle is derived in Appendix A. Some approximate perfon'nance calculations of a Carbon dioxide engine for the present application are shown in Appendix B.
  • FIG. 7 which shows the ideal thermodynamic cycle of the engine, assume unit mass of working medium. In the ideal cycle, the regenerator has an efficiency of percent.
  • a method as claimed in claim 1 wherein said first and second spaces together form a fixed volume, the respective spaces being separated by a movable member within said fixed volume and wherein the net force acting on the said movable member at any time is due to pressures acting upon opposite sides thereof.
  • Apparatus for the conversion of energy available in a thermal source into mechanical energy using a gaseous working medium comprising in succession:
  • heat exchanger output means for adding heat at substantially constant pressures to the compressed medium
  • expansion means for nominally adiabatic expansion of the said compressed and heated medium through an expansion ratio R where R is numerically greater than r
  • v. means connecting items (iv) and (i) to divert a first portion of the energy converted in the expansion means to drive said compression means
  • heat exchanger input means operatively associated with the said heat exchanger output means for extracting heat at substantially constant pressure from the expanded medium and for providing the added heat in step (ii),
  • cooling means for extracting further heat at substantially constant pressure from the expanded medium
  • viii means to divert a second portion of the energy converted in the expansion means to a mechanical output
  • ix means for repeatively cycling items (i) to (viii) in succession.
  • Apparatus as claimed in claim 5 wherein there is a single cylinder and piston common to items (i) and (iv), said cylinder including inlet and outlet valves.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
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US878817A 1969-02-14 1969-11-21 Heat engines Expired - Lifetime US3667215A (en)

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DE (1) DE1957174A1 (en, 2012)
FR (1) FR2030932A5 (en, 2012)
GB (1) GB1259653A (en, 2012)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1985001988A1 (en) * 1983-11-02 1985-05-09 Mitchell Matthew P Improved stirling cycle engine and heat pump
US6418707B1 (en) * 2000-09-07 2002-07-16 Marius A. Paul General advanced power system
US20100192566A1 (en) * 2009-01-30 2010-08-05 Williams Jonathan H Engine for Utilizing Thermal Energy to Generate Electricity
US20120317972A1 (en) * 2010-04-05 2012-12-20 Harold Lee Carder Two cycles heat engine
US20150285183A1 (en) * 2012-11-20 2015-10-08 Dulob Ab Hot gas engine
ES2639589A1 (es) * 2016-04-26 2017-10-27 Universidade Da Coruña Ciclo combinado de motor de combustión interna y máquina alternativa de doble efecto, procesos cerrados y movimiento continuo
US10982543B2 (en) * 2017-03-10 2021-04-20 Barry W. Johnston Near-adiabatic engine
US20240027128A1 (en) * 2022-07-25 2024-01-25 Sapphire Technologies, Inc. Conditioning gas for a pipeline
US20240026803A1 (en) * 2022-07-25 2024-01-25 Sapphire Technologies, Inc. Cooling gas recovered from a well
US20240026851A1 (en) * 2022-07-25 2024-01-25 Sapphire Technologies, Inc. Energy recovery from a gas well

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2869830A (en) * 1948-03-05 1959-01-20 Power Jets Res & Dev Ltd Method and apparatus for heating fluid

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2869830A (en) * 1948-03-05 1959-01-20 Power Jets Res & Dev Ltd Method and apparatus for heating fluid

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1985001988A1 (en) * 1983-11-02 1985-05-09 Mitchell Matthew P Improved stirling cycle engine and heat pump
US6418707B1 (en) * 2000-09-07 2002-07-16 Marius A. Paul General advanced power system
US20100192566A1 (en) * 2009-01-30 2010-08-05 Williams Jonathan H Engine for Utilizing Thermal Energy to Generate Electricity
US8096118B2 (en) 2009-01-30 2012-01-17 Williams Jonathan H Engine for utilizing thermal energy to generate electricity
US20120317972A1 (en) * 2010-04-05 2012-12-20 Harold Lee Carder Two cycles heat engine
US9945321B2 (en) * 2012-11-20 2018-04-17 Dulob Ab Hot gas engine
US20150285183A1 (en) * 2012-11-20 2015-10-08 Dulob Ab Hot gas engine
ES2639589A1 (es) * 2016-04-26 2017-10-27 Universidade Da Coruña Ciclo combinado de motor de combustión interna y máquina alternativa de doble efecto, procesos cerrados y movimiento continuo
US10982543B2 (en) * 2017-03-10 2021-04-20 Barry W. Johnston Near-adiabatic engine
US20240027128A1 (en) * 2022-07-25 2024-01-25 Sapphire Technologies, Inc. Conditioning gas for a pipeline
US20240026803A1 (en) * 2022-07-25 2024-01-25 Sapphire Technologies, Inc. Cooling gas recovered from a well
US20240026851A1 (en) * 2022-07-25 2024-01-25 Sapphire Technologies, Inc. Energy recovery from a gas well
US12258887B2 (en) * 2022-07-25 2025-03-25 Sapphire Technologies, Inc. Cooling gas recovered from a well
US12286953B2 (en) * 2022-07-25 2025-04-29 Sapphire Technologies, Inc. Energy recovery from a gas well

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FR2030932A5 (en, 2012) 1970-11-13
GB1259653A (en, 2012) 1972-01-12
CH528015A (fr) 1972-09-15
DE1957174A1 (de) 1970-08-27

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