Showing papers on "Thermodynamic cycle published in 1977"

Thermodynamics in finite time: extremals for imperfect heat engines

Abstract: A general description is developed for processes involving work and two heat reservoirs or three heat reservoirs in terms of rates for continuous processes or of cycle averages for periodic processes. The description is applied to heat engines having friction, thermal resistance, and heat losses in order to determine the maximum power and maximum efficiency of such engines. By use of a geometric representation the reversible and irreversible parts of a process are separated as the components of a vector. This leads to the definition of a dimensionless quantity that measures irreversibility and is related in a complementary way to the traditional concept of efficiency. The new quantity appears to be useful in cases where efficiency has no well‐defined meaning.

High temperature refrigerator

Abstract: A high temperature magnetic refrigerator which uses a Stirling-like cycle in which rotating magnetic working material is heated in zero field and adiabatically magnetized, cooled in high field, then adiabatically demagnetized. During this cycle said working material is in heat exchange with a pumped fluid which absorbs heat from a low temperature heat source and deposits heat in a high temperature reservoir. The magnetic refrigeration cycle operates at an efficiency 70% of Carnot.

Method and device for balanced compounding of Stirling cycle machines

Abstract: A multi-cycle thermal reciprocating machine of the type commonly known as Stirling engine, which operates on a closed cycle with a compressible fluid as the operational medium. Double-acting pistons are combined into reciprocating members, each of which is in contact with the operational medium of at least four different Stirling cycles. These cycles occur simultaneously and are symmetrically phased, each performed in at least two different expansible chambers at two different temperatures, typically one hot expansion chamber connected to a cold compression chamber through a conduit containing two heat exchangers and one regenerator. The piston surfaces are arranged in opposed pairs, two pairs of surfaces being maintained at a constant distance apart and so located that the movement of each reciprocating member is caused by one co-acting pair of expansion chambers being part of one pair of thermodynamic cycles in phase opposition to each other, and a second co-acting pair of compression chambers being part of a second pair of cycles also in phase opposition to each other, and in a quadrature relationship with the first pair of cycles. Each cycle is effected by two reciprocating members in such a manner that the compression forces of one cycle are internally balanced by the expansion forces of another cycle, so that in consequence there is a smooth flow of power and the forces transmitted are reduced. The resulting Stirling engines are flexible in design and versatile in application.

Liquid piston heat-actuated heat pump and methods of operating same

Abstract: A heat-actuated heat pump is disclosed having liquid pistons which displace the working gas and transmit power between expanding gas and compressing gas Power output from expanding sections is transmitted to compressing sections without intervening mechanical shafts or levers, and the phasing of the various pistons is self-regulated, thereby eliminating the need for phase control mechanisms, such as crankshafts The engine and heat pump operate in a thermally regenerated cycle without valves, closely approximating a Stirling cycle

Magnetic stirling cycles--A new application for magnetic materials

Abstract: There is the prospect of a fundamental new application for magnetic materials as the working substance in thermodynamic cycles. Recuperative cycles which use a rare-earth ferromagnetic material near its Curie point in the field of a superconducting magnet appear feasible for applications from below 20K to above room temperature. The elements of the cycle, advanced in an earlier paper, are summarized. The basic advantages include high entropy density in the magnetic material, completely reversible processes, convenient control of the entropy by the applied field, the feature that heat transfer is possible during all processes, and the ability of the ideal cycle to attain Carnot efficiency. The mean field theory is used to predict the entropy of a ferromagnet in an applied field and also the isothermal entropy change and isentropic temperature change caused by applying a field. Results are presented for J=7/2 and g=2. The results for isentropic temperature change are compared with experimental data on Gd. Coarse mixtures of ferromagnetic materials with different Curie points are proposed to modify the path of the cycle in the T-S diagram in order to improve the efficiency or to increase the specific power.

Process for the recovery of mechanical work in a heat engine and engine for carrying out the process

Abstract: In a process for recovering mechanical work in a heat engine there is used as a working medium in the heat engine a gas to which vapor is added having a H-value lower than the H-value of the gas, the gas being caused to absorb the condensation heat from the vapor by condensation of the vapor under essentially isothermal expansion. A heat engine for carrying out the process comprises; an isothermal compressor to which a liquid injection mechanism is connected; an isentropic compressor; an expansion machine to which a vapor generator is connected; and at least one additional expansion machine with liquid separator; said compressors and expansion machines being included in a closed circulation system for the gas serving as a working medium.

Energy extraction characteristics of hot dry rock geothermal systems

Abstract: The LASL Hot Dry Rock Geothermal Energy Project is investigating methods to extract energy at useful temperatures and rates from naturally heated crustal rock in locations where the rock does not spontaneously yield natural steam or hot water at a rate sufficient to support commercial utilization. Several concepts are discussed for application to low and high permeability formations. The method being investigated first is intended for use in formations of low initial permeability. It involves producing a circulation system within the hot rock by hydraulic fracturing to create a large crack connecting two drilled holes, then operating the system as a closed pressurized-water heat-extration loop. With the best input assumptions that present knowledge provides, the fluid-flow and heat-exchange calculations indicate that unpumped (buoyant) circulation through a large hydraulic fracture can maintain a commercially useful rate of heat extraction throughout a usefully long system life. With a power cycle designed for the temperature of the fluid produced, total capital investment and generating costs are estimated to be at least competitive with those of fossil-fuel-fired and nuclear electric plants. This paper discusses the potential of the hot dry rock resource, various heat extraction concepts, prediction of reservoir performance, and economic factors, andmore » summarizes recent progress in the LASL field program.« less

Multiple well dual fluid geothermal power cycle

Abstract: Heat energy from hot geothermal fluids supplied by different temperature wells is transferred by heat exchange into a power fluid cycle, preferably of the dual fluid type, at different points in the cycle, which both enables an increase in peak cycle temperature to be achieved and allows more heat energy to be transferred into lower temperature points in the cycle. The result is an increase in the amount of power which can be developed per unit of geothermal fluid supplied.

Thermodynamic processes induced by coherent radiation

Abstract: It is shown by quantum statistics that under certain stated conditions the entropy of coherent radiation is zero and it is still negligible for multimode laser operation. This makes possible gas kinetic processes which, to a small extent, have already been observed or even utilized, but which can be greatly enhanced by an optimized choice of molecular structures and radiation conditions. Radiative cooling of gases is discussed in detail. The conditions for maximum heat withdrawal are derived, and it is proposed that the processes of cooling and relaxation heating can be sufficiently separated in time to achieve certain effects and thermodynamic cycles. One of these is the complete conversion, possible in principle, of coherent radiation into work. This concept is based on a heat pump process followed by heat‐to‐work conversion, the heat rejected being just equal to that withdrawn by radiation. The conditions for complete conversion turn out to be the same as for maximum heat withdrawal. The feasibility of these processes depends on the degree to which practical conditions can be met, and on the validity of certain assumptions which have to await experimental verification.

Installation for the production of energy which utilizes a source of heat or natural thermic differences in level

Abstract: An installation and a method for the production of energy which utilize a source of heat or natural thermic differences are described. A first container contains a fluid in the liquid state and is capable of transmitting the heat to the fluid, a second container being used for holding the fluid after completion of the thermodynamic cycle and after it has returned to the liquid state, the second container being at a temperature lower than the temperature which prevails in the first container. Conduit means for connecting the first and second container are provided. The fluid has a low boiling point and is capable of undergoing a change from the liquid to gaseous state. A turbine or equivalent device is provided to utilize the kinetic energy of the fluid and transform this energy into mechanical energy; the fluid is converted from the liquid to the gaseous state upon entry into this device and returns to the liquid state in the interior of the second container. The operation may be reversed with the second container being exposed to the source of heat.

Molten salt thermal energy storage for utility peaking loads

Abstract: This paper considers the use of thermal energy storage (TES) in molten salts to increase the capacity of power plants. Five existing fossil and nuclear electric utility plants were selected as representative of current technology. A review of system load diagrams indicated that TES to meet loads over 95% of peak was a reasonable goal. Alternate TES heat exchanger locations were evaluated, showing that the stored energy should be used either for feedwater heating or to generate steam for an auxiliary power cycle. Specific salts for each concept are recommended. Design layouts were prepared for one plant, and it was shown that a TES tube/shell heat exchanger system could provide about 7% peaking capability at lower cost than adding steam generation capacity. Promising alternate heat exchanger concepts were also identified.

Solar engine called, bellows solar engine

Abstract: A reciprocating engine for water pumping or air circulation is disclosed which uses solar energy from a black box collector or other low temperature heat source to expand and contract bellows thereby providing large forces with low pressures by taking advantage of large working areas available with bellows. The engine is essentially a constant pressure, variable volume thermodynamic cycle engine having a compressor, a heater and a driver with the compressor and the driver sections both being bellows, the driver being capable of operating the compressor section by means of the former enjoying a force advantage or a mechanical advantage over the later.

Computer program for determining the thermodynamic properties of Freon refrigerants

Abstract: This program was written to be used as a subroutine. The program determines the thermodynamics of Freon refrigerants. The following refrigerants can be analyzed F-11, F-12, F-13, F-14, F-21, F-22, F-23, F-113, and F-114. The subroutine can evaluate a thermodynamic state for these refrigerants given any of the following pairs of state quantities: pressure and quality, pressure and entropy, pressure and enthalpy, temperature and quality, temperature and specific volume, and temperature and pressure. These six pairs of knowns allow the user to analyze any thermodynamic cycle utilizing a refrigerant as the working fluid. The Downing form of the Martin equation of state was used. This report contains a brief description, flow chart and listing of all subroutines required.

Domestic or industrial building heater - effecting mechanical operations necessary for thermodynamic cycle almost reversibly, with high efficiency

Abstract: An installation for heating buildings used as dwellings or industrially makes use of a gas which is in contact alternately with a cold source and a hot source by means of inlet and outlet heat exchangers and a compressor which circulates the gas. The gas describes a thermodynamic cycle in a closed circuit. The exchangers connects points of the circuit situated at different heights in a natural or artificial gravity field. The gas has a lower specific heat capacity than the air and undergoes substantially isothermal press. changes. It exchanges heat with a liquefiable fluid of high latent heat. Typically, the gas is argon and the fluid is pentane. The installation operates in a cycle which approaches closely thermodynamic reversibility. It is simpler and is more efficient than existing installations using a fluid which changes its physical state, and rotary machines, in several stages, of low efficiency because of thermodynamic irreversibility.

Thermodynamic and cost optimization using program GEOTHM

Abstract: Some of the features of the computer program GEOTHM are shown This program designs and optimizes thermodynamic process cycles Several examples of geothermal cycle optimization are given Three dimensional plots generated by the computer show how the optimization process works

Effects of film injection on performance of a cooled turbine

Abstract: Some of the most dramatic increases in the performance of turbojet and turbofan aircraft engines have been obtained as a result of increased thermodynamic cycle temperatures made possible by the use of film cooling techniques. The realization of the potential performance gains, however, is only possible if the quantity of cooling air and the aerodynamic mixing losses resulting from the injection of coolant in the form of film on the flowpath surfaces are minimized. Such a minimization requires a more complete understanding of the relationship between cooling and aerodynamics. A review is conducted of tests which have been conducted to determine the effects of coolant injection on turbine performance. The results obtained in the tests are compared with an analytical technique developed for predicting coolant injection effects. Particular attention is given to the effects of turbine cooling on overall cycle thermodynamic efficiency, taking into account incremental changes in turbine thermodynamic efficiency for various incremental changes in coolant flow rate.

Assessment of technologies for research, development, and demonstration of industrial cogeneration and waste heat recovery in the near term. Final report

Abstract: The status of advanced power systems that have the potential, when developed, of contributing to the generation of electricity in combination with process steam in the time frame from the present to 1985 to 1990 is studied. The study considered the use of heat pumps driven by cogeneration plants; combined steam-gas turbine cycles; diesel topping; open cycle gas turbines; small high-efficiency steam turbines; closed Brayton cycle; the Stirling engine; fuel cells; and thermionics and MHD. The methodology and cost analysis of each technology and projections of fuel savings are presented. Technical and economic analyses of alternatives for recovery of waste heat in the chemical, petroleum refining, and paper and pulp industries are considered. Considered were combustion air preheating, steam generation, or electrical generation from waste flue gases in ammonia, ethylene, and styrene manufacturing in the chemical industry and crude distillation, catalytic reforming, coking and hydrocracking in petroleum refining. Also considered were product heat effluent heat exchange in ethylene and styrene manufacturing and crude distillation in petroleum refining; power recovery from pressurized product streams in catalytic cracking; and drying and product stream heat exchange in the paper and pulp industry. Potential fuel savings for each of these technologies was estimated. Majormore » conclusions are summarized. (MCW)« less

Solar Residential Electrification with High-Performance Heat Engines

Abstract: Application of high-performance closed-cycle heat engines to solar energy conversion for residences and other buildings is considered Stirling and recuperated Brayton cycles are investigated with the former favored due to commonality in construction with conventional small Otto cycle engines Typical top temperatures of these cycles is near best compromise between thermodynamic efficiency vs solar collection efficiency The overall system includes an array of sun-following paraboloidal collectors connected by sodium heat pipes Both heat and electrical buffering, control problems, accoutrements (such as heat pumps), other heat sources, and other electrical sources are examined Analogous conversion of furnace fuel energy into electricity is considered

Heat transfer research and power cycle transient modeling

Abstract: Fine axial flutes enhance heat transfer in vertical shell-and-tube exchangers with water inside the tubes and ammonia evaporating or condensing in layer flow on the shell side. Single-tube experiments with R-11 and ammonia indicate local shell-side coefficients 3 to 5 times those for corresponding smooth tubes. Single-tube experiments with water indicate that at moderate velocities the tube-side coefficients are enhanced by a factor equal to the ratio of fluted-to-smooth surface areas while the fluid friction is similarly increased. The experimental data are transformed into mean individual coefficients for ammonia and water. Overall coefficients for a particular case are presented to illustrate the efficacy of enhancement by flutes on one or both sides of the heat transfer surface. Means are described for using emerging data to predict the static and dynamic behavior of the power cycle and the interactions of components throughout the complete power plant.

Development of a geothermal binary cycle simulator

Abstract: Presented are the logic and methodology used to develop a computer program for simulation of the geothermal binary cycle energy conversion process using both pure fluids and mixtures as working fluids. The simulation was developed sequentially to three levels of description: (a) thermodynamic cycle, (b) equipment sizing, and (c) capital cost specification. Pertinent background information, formulas, and computation methods are discussed.