Showing papers on "Thermodynamic cycle published in 1979"

A pistonless Stirling engine—The traveling wave heat engine

Abstract: The propagation of acoustical waves through a differentially heated regenerator results in gas in the regenerator undergoing a Stirling thermodynamic cycle. One direction of wave propagation results in amplification of the waves and conversion of thermal energy into acoustical energy. The opposite direction results in acoustical energy being used to pump heat. The ideal gain and maximum energy conversion rates are derived in this paper. Low power gain measurements were made which verify the derived gain equation. Practical engines and heat pumps using this principle are discussed.

Optimal configuration of a class of irreversible heat engines. I

Abstract: In a previous paper we analyzed a class of irreversible cyclic heat engines to find their optimal operating configuration for specific performance goals. In that paper the thermodynamic variables of the working fluid were not treated as dynamical variables, instead the dynamics was replaced by an integral constraint. In this paper we reanalyze the same class of heat engines treating the thermodynamic variables of the working fluid as dynamical variables, and we obtain the optimal configuration of the engine when the performance goal is to maximize the average power output per cycle or, alternatively, to maximize the efficiency of the engine. To carry through this program it is necessary to use mathematical techniques from optimal-control theory. Since this subject is unfamiliar to most physicists and chemists, we briefly introduce some of the central ideas of the theory.

Use of organic working fluids in Rankine engines

Abstract: A compilation is presented of state-of-the-art data on the use of organic working fluids in operational Rankine cycle engines. Particular attention is given to the determination of the maximum temperatures used for various working fluids in operational Rankine cycle engines and identification of thermal instability and chemical reaction problems related to these temperatures. Information is included on the characteristics and selection of working fluids; the behavior of lubricating oils in contact with working fluids; operational experience; and recommended organic fluids R and D. (LCL)

Ceramics in Heat Engines

Abstract: Recent improvements in high performance ceramics have given a new impetus for the advancement of heat engines. The thermal efficiencies of the Otto, Diesel, Brayton, and the Stirling cycle can now be improved by higher operating temperatures, reduced heat loss, and exhaust energy recovery. Although physical and chemical properties of the high performance ceramics have been improved significantly, they still fall short of meeting the requirements necessary for application and commercialization of advanced heat engine concepts. Aside from the need for greater strength, the problems of consistency, quality, design, material inspection, insulative properties, oxidation, and other important features must be solved before high performance ceramics can be considered a viable material for advanced heat engines. Several approaches in developing an adiabatic engine design in the laboratory are shown. Other possible future improvements such as the minimum friction unlubricated engine through the use of ceramics are also described.

Effect of partial suppression of heat loss to coolant on the high output diesel engine cycle

Abstract: The paper describes the results of a detailed cycle analysis applied to a high output 6 cylinder truck diesel engine: 1) conventional form; 2) with a uniformly distributed layer of silicon nitride giving approximately isothermal wall conditions; and 3) with adiabatic wall conditions. For case (1) the benefits are largely limited to increased exhaust enthalpy, suggesting the desirability of turbocompounding. Case (2) gives marked improvement in cycle efficiency as well as raised exhaust enthalpy. Paper number 790823.

Heat and liquid recovery using open cycle heat pump system.

Abstract: Recovery of heat and/or condensable liquid from a gaseous environment utilizing an open cycle heat pump system. The open cycle heat pump system is employed to alter the temperature of a gas by compression (1), expansion (5), heat exchange (3), and combinations thereof, to condense select vapors carried in the gaseous environment for removal from the gas. The open cycle heat pump system can also be used to extract the heat from a gas for use as desired. The invention also relates to recovering condensable solvent and/or heat from gas streams employed in drying ovens (41) used in processing solvent-laden materials.

Analysis of binary thermodynamic cycles for a moderately low-temperature geothermal resource

Abstract: Analyses of a number of geothermal binary-cycles were made with the objective of finding a cycle which can produce low-cost electrical energy from a moderately low-temperature geothermal resource. Cycles were screened which included isobutane, pentane, cis-2-butene, and several mixed-hydrocarbon working fluids. Dual- and triple-boiling cycles were analyzed. Both shell-and-tube and direct-contact boilers, heaters, and condensers were assessed. A geothermal fluid (geo-fluid), typical of Raft River resource conditions was assumed, which has a temperature of 290/sup 0/F and 52 parts per million dissolved nitrogen. Special emphasis in the analyses was directed toward investigation of several methods for keeping the loss of working fluid for the cycle at an acceptable level. It was concluded that for the Raft River geo-fluid, the direct-contact cycle has a potential for net geofluid utilization effectiveness values, (watt-hr/lbm geo-fluid) equivalent to those of the shell-and-tube cycle. Therefore, because of the lower cost of direct-contact components, a potential exists for the direct-contact plant to produce lower cost electrical energy than a comparable shell-and-tube plant. Advanced cycles were assessed which showed improvements in net geo-fluid utilization effectivness, relative to the first Raft River 5-MW Pilot Plant (dual-boiling, shell-and-tube isobutane cycle), of up to 19%.

Open cycle heat pump system and process for transferring heat

Abstract: Two or more open cycle vapor compression heat pumps of interdependently different capacities are placed in parallel arrangement intermediate a heat sink and a heat source for the transfer of sensible heat therebetween.

The role of interfacial heat and mechanical energy transfers in a liquid-metal MHD generator

Abstract: A brief description of the two-phase liquid-metal MHD power generation cycle and its advantages is provided. The importance of good interfacial liquid to gas heat transfer is discussed, and data confirming that satisfactory heat transfer is indeed achieved in an experimental generator is presented. An expression for the effect of the velocity difference between the gas and the liquid on generator performance is derived. An ‘equivalent turbine’ efficiency is defined to characterize the generator as part of a heat engine and related to experimental data.

Research and development of an air-cycle heat-pump water heater. Final report

Abstract: A prototype reverse Brayton air cycle heat pump water heater has been designed and built for residential applications. The system consists of a compressor/expander, an air-water heat exchanger, an electric motor, a water circulation pump, a thermostat, and fluid management controls. The prototype development program consisted of a market analysis, design study, and development testing. A potential residential market for the new high-efficiency water heater of approximately 480,000 units/y was identified. The retail and installation cost of this water heater is estimated to be between $500 and $600 which is approximately $300 more than a conventional electric water heater. The average payback per unit is less than 3-1/2 y and the average recurring energy cost savings after the payback period is approximately $105/y at the average seasonal coefficient of performance (COP) of 1.7. As part of the design effort, a thermodynamic parametric analysis was performed on the water heater system. It was determined that to obtain a coefficient of performance of 1.7, the isentropic efficiency of both the compressor and the expander must be at least 85%. The selected mechanical configuration is described. The water heater has a diameter of 25 in. and a height of 73 in. The resultsmore » of the development testing of the prototype water heater system showed: the electrical motor maximum efficiency of 78%; the compressor isentropic efficiency is 95 to 119% and the volumetric efficiency is approximately 85%; the expander isentropic efficiency is approximately 58% and the volumetric efficiency is 92%; a significant heat transfer loss of approximately 16% occurred in the expander; and the prototype heat pump system COP is 1.26 which is less than the design goal of at least 1.7. Future development work is recommended.« less

The Reversed Brayton Cycle Heat Pump—A Natural Open Cycle for HVAC Applications

Abstract: Using reasonable assumptions for turbomachinery efficiencies and heat exchanger effectivenesses, the Coefficient of Performance (COP) and Specific Heating Effect (SHE) of the regenerated and unregenerated cycles are computed and optimized. Only heating data are presented and both open and closed cycles are considered. An effort is made to indicate those cases where (the working fluid being air) the cycle may be appropriately open to combine the heating function with ventilation. When driven by an appropriately small direct Brayton cycle prime mover, the total potential for a new and widespread gas turbine application of literally millions of units becomes defined.

User's manual for PRESTO. A computer code for the performance of regenerative superheated steam-turbine cycles

Abstract: PRESTO is a computer code developed at the Oak Ridge National Laboratory (ORNL) to analyze the performance of regenerative steam-turbine cycles using superheated steam such as that normally available from large fossil-fueled steam generators. Throttle pressures may be either sub- or supercritical. The turbine arrangement may be tandem- or cross-compound and have zero, one, or two reheaters. Cycles modeled for study may thus range from a single one-section nonextraction cycle to a three-section cycle with multiple reheat. The computer code is also designed to analyze the performance of steam-turbine cycles containing such additional features as steam induction, extraction, and feedwater heating by an external heat source. These features allow the user to combine the steam-turbine cycle with a high-temperature topping cycle or to integrate it with an advanced-concept heat source. This manual has been divided into three major sections, i.e., a general description of the code's methodology, which will give a basic understanding of the code; a description of the options built into the code to handle cogeneration cycles, peaking units, etc; and instructions for the data input preparation. The PRESTO computer code is written in standard FORTRAN IV for the IBM 360/370 series of digital computers.

Waste heat boiler and heat exchange process

Abstract: A system for recovering waste heat from a stream of heated gas is disclosed. The system includes a convection heat transfer chamber, a boiler tank, and a plurality of heat pipes thermally interconnecting the convection heat transferchamber with the boiler tank. Each of the heat pipes includes an evaporator section which is disposed in heat transfer relation with a stream of heated gas flowing through the convection heat transfer chamber, and a condenser section disposed in heat transfer relation with a volume of water disposed within the boiler tank. The evaporator sections and condenser sections are totally enclosed within the convection heat transfer chamber and boiler tank, respectively, and are connected in closedcycle fluid communication with each other. The heat pipes contain a working fluid which is characterized by a thermodynamic cycle in which the working fluid is vaporized in the evaporator section and flows to the condenser section where it is condensed to the liquid phase and returns in a closed cycle to the evaporator section, thereby transferring heat energy from the heated gas stream in the convection heat transfer chamber to the volume of water contained in the boiler tank. In a regenerative arrangement, exhaust gas discharged from the convection heat transfer chamber is recycled to the input of the convection heat transfer chamber to provide high mass flow at low velocity for optimum efficiency. In another arrangement, superheated steam is provided by a pair of heat pipe boilers whose convection heat transfer chambers are connected in series, with the evaporator of the steam generating unit being located downstream of the superheat unit and the input of the superheat unit being the steam output of the steam generating unit.

Heat cycle system and method for producing fresh water from brine

Abstract: Steam, for example, is produced from aqueous brine, by a system that employs preferably hot waste fluid, and nozzle means and rotary separator means generally of a known kind per se. The method steps include transferring the waste heat of combustion source (22) to the brine flowing in heater exchanger coil (23), expanding the hot brine through nozzle means (24) to form a jet of steam and liquid droplets, causing said expanded flow to rotate the rotary separator means (26) for forming a liquid layer of said droplets on the separator means by centrifugal action while separating the steam (at 28), which is used to heat the incoming brine pumped by pump (11) in condensers (14, 13). The separated liquid from the rotating layer is used to drive turbine means (29) and the condensed steam provides fresh water from the brine. Several stages of separators may be employed in series or in series and parallel. Also, the steam may be used to assist in power generation. The system described is of low first cost and low operating cost, and is simple and reliable.

Solar-fossil hybrid power system using a combined cycle

Abstract: A solar central receiver hybrid power system concept which uses a gas turbine/heat recovery steam generator/steam turbine combined cycle to generate electricity from both solar and fossil fuel energy is described. The concept description dwells primarily on a near term 100 MWe (net) system that utilizes a state-of-the-art combined cycle with a gas turbine inlet temperature of 1093/sup 0/C (2000/sup 0/F). This system is implementable in the 1985 time frame. An advanced system that uses an inlet temperature of 1316/sup 0/C (2400/sup 0/F) is also described. Performance comparisons of these two systems are given. Major advantages of the system concept as well as its technical issues are highlighted.

Internal heater module for cryogenic refrigerators and Stirling heat engines

Abstract: Heat energy is supplied to the hot volume of a Vuilleumier cycle cryogenic refrigerator, or to a Stirling cycle heat engine, with and by the inventive heater module which is disposed within the hot working volume of the machine. The heater module is in contact with the working fluid within the hot volume, thereby more efficiently supplying heat energy to the machine. This invention accomplishes heat input to the most optimum place, namely: inside the hot volume. A preferred embodiment and a variation are taught.

Quasi Equilibrium Fuel-Air Heat Balanced Cycle Analysis.

Abstract: : The quasi equilibrium thermodynamic model of the Naval Academy Heat Balanced Engine (NAHBE) has been modified to include the influence of fuel-air chemistry on predicted indicated engine performance. Heat addition to the Air Standard Heat Balanced Cycle was expressed in terms of an appropriate fuel-air ratio and heating value for a standard fuel. Indicated parameters including mean effective pressure, peak pressure, specific fuel consumption and thermal efficiency for compatible Otto and Heat Balanced cycles were calculated and compared. Performance parameters for both cycles were obtained at equal compression ratios, fuel-air ratios, fuel type, and engine rpm. Results show that for overall stoichiometric heat addition the Heat Balanced cycle can produce greater indicated engine power, higher indicated thermal efficiency and lower indicated specific fuel consumption than the corresponding Otto cycle. Further analysis indicates that the optimum heat balancing conditions occur for constant volume heat addition with rich mixture composition followed by constant pressure heat addition with lean composition. (Author)

Experimental performance study of a series solar heat pump

Abstract: To provide energy conservation for space heating, a vapor compression heat pump can be used to elevate temperatures which are above ambient but insufficient in themselves for comfortable conditioning. The Solar Assisted Heat Pump (SAHP) falls into this category, using low temperature, hence potentially inexpensive, collectors which provide input temperatures in the 40 to 100/sup 0/F range. Since little experience or data of heat pump operation at the high evaporating temperatures is available, an experimental study is being carried out in the Brookhaven National Laboratory (BNL) Solar Laboratory using a specially constructed solar heat pump simulator to study performance and component characteristics while attempting to obtain Coefficients of Performance (COP) which track the increasing trend with evaporating temperature dictated by the Carnot and Ideal Vapor Cycles. This paper reports the results of the initial phase, wherein a residential size liquid-to-liquid heat pump assembled from off-the-shelf components was tested. Results showed that a substantially increasing COP, which follows theory, was attainable at evaporating temperatures as high as 98/sup 0/F by using variable compressor speed, large heat exchangers, and proper selection of expansion device. A discussion of how this performance could be utilized in a complete SAHP system is included. The resultsmore » apply also to heat pump non-solar sources such as reclaim or geothermal heat.« less

Heating system using a closed thermodynamic cycle heat pump - having four stages, used for heating buildings in driers etc.

Abstract: The stages in the cycle are compression, condensation, expansion and vaporisation-followed by recompression. The fluid used in the cycle is a non-azeotropic mixt. Each stage of the process is a multistage process to use the different condensation and evaporation characteristics of the various mixt. components. The heat removed from the mixt. as it condenses passes into a heating system. Heat for vaporising the liq. is taken from an external source such as the air, a stream or a lake. The use of the multistage process increases the system efficiency. It may be used efficiently where there is a big temp. difference between the hot and cold source. It is relatively simple in regard to the equipment needed and its control and regulation.

An Initial Model for the Finite Displacement Response Characteristics of a Fluidyne Pump.

Abstract: : This paper is the final report on the independent laboratory in house research (ILIR) sponsored work by the Harry Diamond Laboratories on the Fluidyne pump. The effort started with a survey of the extant literature on the subject, continued with experimental observations that led to a mathematical model, and has culminated with a comprehensive statement on the physical operation of the pump. The literature is particulary sparse on the subject; hence, only the basic references are cited. The report presents a detailed mathematical model of the fluid mechanical and thermodynamic processes occurring during oscillation. A positive-feedback simulation model is postulated that demonstrates, for the first time, physically why there is an onset of oscillations and subsequent sustained motion. This model is based on actual observations of the startup process in a prototype pump. The initially reported thermodynamic efficiency of this heat engine was less than 0.3 percent. Currently, Fluidyne pumps have demonstrated efficiencies of about 2 percent. The peak efficiencies, however, may theoretically approach 10 percent. The mathematical model has shown that large losses occur in the heat transfer to the working gas, heat losses to the displacer liquid, and friction in the output line. Improvements in these areas may dramatically improve the observed overall efficiency. The efficiency of the cycle itself, that is, the work done by the thermodynamic cycle relative to the output work, is on the order of 10 percent.

Alternate cycles applied to ocean thermal energy conversion

Abstract: Four open cycle OTEC concepts are described. These are: (1) single, vertical-axis turbine; (2) multiple, horizontal-axis turbines; (3) foam lift/hydraulic turbine; and (4) mist lift/hydraulic turbine. A preliminary assessment of achievable performance is made in addition to a description of the subsystem performance objectives which would support the achievement of the full potential inherent in these concepts. The results and conclusions of the paper include a description of the research objectives, achievement of which make open cycle OTEC a viable alternative as a nationl energy source.

Heat engine using air heat - comprises two cylinder machine giving adiabatic expansion followed by isothermal compression

Abstract: The heat engine uses air heat, comprising a two-cylinder piston machine in which the air undergoes a three-stage quasi-open process - adiabatic expansion, followed by isothermal compression and isobar heat absorption. To remove the waste heat released on isothermal compression a heat pump is inserted. This transfers this heat to the cold air leaving the machine, including the compression heat of the heat pump with a relatively small temp. drop.

Analysis of binary thermodynamic cycles for a moderately low-temperature geothermal resource

Abstract: Analyses of a number of geothermal binary-cycles were made with the objective of finding a cycle which can produce low-cost electrical energy from a moderately low-temperature geothermal resource. Cycles were screened which included isobutane, pentane, cis-2-butene, and several mixed-hydrocarbon working fluids. Dual- and triple-boiling cycles were analyzed. Both shell-and-tube and direct-contact boilers, heaters, and condensers were assessed. A geothermal fluid (geo-fluid), typical of Raft River resource conditions was assumed, which has a temperature of 290/sup 0/F and 52 parts per million dissolved nitrogen. Special emphasis in the analyses was directed toward investigation of several methods for keeping the loss of working fluid for the cycle at an acceptable level. It was concluded that for the Raft River geo-fluid, the direct-contact cycle has a potential for net geofluid utilization effectiveness values, (watt-hr/lbm geo-fluid) equivalent to those of the shell-and-tube cycle. Therefore, because of the lower cost of direct-contact components, a potential exists for the direct-contact plant to produce lower cost electrical energy than a comparable shell-and-tube plant. Advanced cycles were assessed which showed improvements in net geo-fluid utilization effectivness, relative to the first Raft River 5-MW Pilot Plant (dual-boiling, shell-and-tube isobutane cycle), of up to 19%.