Showing papers on "Thermal efficiency published in 1978"

Applied Thermodynamics for Engineering Technologists

Abstract: 1 Introduction And The First Law Of Thermodynamics 2 The Working Fluid 3 Reversible And Irreversible Processes 4 The Second Law 5 The Heat Engine Cycle 6 Mixtures 7 Combustion 8 Steam Cycles 9 Gas Turbine Cycles 10 Nozzles And Jet Propulsion 11 Rotodynamic Machinery 12 Positive Displacement Machines 13 Reciprocating Internal-Combustion Engines 14 Refrigeration And Heat Pumps 15 Psychometry And Air-Conditioning 16 Heat Transfer 17 The Sources, Use And Management Of Energy

Two Thermodynamic Optima in the Design of Sensible Heat Units for Energy Storage

Abstract: The paper presents a treatment of sensible-heat energy storage units as systems intended to store useful work. An analysis of the thermodynamic irreversibilities associated with storing energy from a hot gas source as sensible heat in huge liquid baths points out two important trade-offs. First, there exists an optimum well-defined quantity of hot gas to be used in order to maximize the useful work stored in the liquid bath. Using more than this optimum quantity in the hope of maximizing the amount of thermal energy stored as sensible heat leads to severe thermodynamics losses. Second, there exists an optimum relationship among the gas-liquid heat-exchanger design parameters which minimizes the system irreversibility while maximizing its capability of storing useful work. This relationship provides a procedure for estimating the heat-exchanger optimum number of transfer units. The existence of the two optima demonstrates that designing sensible heat units for maximum thermal energy storage does not necessarily amount to thermodynamically optimizing such systems.

On the efficiency of rate processes. Power and efficiency of heat engines

Abstract: We analyze the power and efficiency of heat engines which operate subject to irreversible heat flow. First, we consider a specific model, with a cycle for an ideal gas similar to that of a reversible Carnot engine (’’isothermal cycle’’), and find the maximum power, and efficiency at the point of maximum power (ηm), for given heat bath temperatures and compression ratio. We prove that the cycle chosen produces more power than any other conceivable cycle in the limit of large compression ratio; the derivation is made for an ideal or van der Waals gas as a working fluid, but this is not restrictive in this limit. We use these results to obtain a general formulation, of upper bounds on power and ηm, valid for isothermal cycles to study the dependence of these quatities on the form of the law of irreversible heat conduction. We find that ηm depends only on the heat bath temperatures and the form of the irreversible rate process, but is independent of the material properties of the system. The dependence of ηm ...

Removal of acid gases from hot gas mixtures

Abstract: A process for removing acid gases such as CO 2 and H 2 S from gas streams using an aqueous alkaline scrubbing solution which is circulated between an absorption and regeneration stage wherein the stripping steam for regeneration is derived at least partly from the hot feed gas to be purified. The thermal efficiency of the process is substantially improved by first heat-exchanging the hot feed gas with the scrubbing solution to raise stripping steam and then heat-exchanging the hot feed gas with water (which is preferably condensate water produced in the scrubbing process) in a second heat exchanger operating under reduced pressure, thus recovering additional low-level heat from the feed gas and producing low-pressure steam which is compressed and then utilized as additional stripping steam. In a preferred embodiment, additional low-pressure steam is generated by also flashing off low-pressure steam from the regenerated scrubbing solution and compressing this steam together with the steam produced in the second heat exchanger for use as stripping steam.

Apparatus for generating thermal energy and electrical energy

Abstract: An apparatus for generating thermal and electrical energy includes an internal combustion engine connected to and adapted to drive a generator for providing electrical power and a brake for generating thermal energy. In one embodiment, a heat carrier flows through appropriate conduits for absorbing heat energy from the brake, from the combustion chamber of the engine, and from the engine exhaust gases and delivers the heat energy to a end-use heat exchanger, for example, a room or space heater. In a second embodiment, the engine exhaust gas flow is used to drive a gas turbine that, in turn, drives a compressor in a thermal cycle to provide additional heat transfer capability.

Apparatus for the combined production of electrical energy and heat

Abstract: Apparatus for the combined production of heat and electrical energy comprising an internal combustion engine driving an electricity generator and enclosed in a thermally insulated housing with heat exchangers for extracting heat from the engine coolant, the engine oil, the exhaust gases from the engine and from the electricity generator, and for transferring this heat to an external heating circuit, in which all the components are carried by a rectangular or cubic supporting framework to which the thermal and acoustic insulation panels are attached by quick-release fastenings, the engine and generator being connected together to form a rigid unit which is suspended from the framework while the ignition equipment of the engine is housed externally of the framework and cooled by the incoming air being drawn into the engine flowing through a housing in which it is supported.

Steam-Drive Correlation and Prediction

Abstract: Studies of the steam injection processes in physical models and with field steam-drive projects support the concept that the oil produced is usually proportional to the steam zone size. Exceptions to this behavior can occur when a small amount of heat is applied to reservoirs in which a substantial amount of primary oil remains, or when initial oil saturation is low. Results of laboratory experiments comparing steam soaks and steam drive are presented. These experiments add to evidence that ultimate thermal efficiency in both processes is largely dependent upon reservoir and steam properties, and project life. Application of this principle often leads to the conclusion that heat can effectively be injected at a high rate initially. A mathematical model using a simple energy balance is developed to compare the results of experimental model studies and field-steam drive projects with the steam zone concept. This model uses basic reservoir parameters and steam properties together with Mandl's theory to calculate steam-zone size and to predict ultimate oil/steam ratio. Results correlate well with field experience and suggest that the model is a useful screening tool for estimation of oil/steam ratio from average reservoir properties.

Internal combustion and steam engine

Abstract: A six-stroke cycle engine fires a fuel charge for a first power stroke, the exhaust gases being directed to a thermally insulated jacket surrounding the cylinder and having fins and/or baffles to recover heat from the gases and conduct the heat to the inner cylinder wall for converting injected water into steam for a second power stroke. The fins and/or baffles in the jacket also function as a muffler for the engine.

Compact thermal energy reservoirs

Abstract: Light weight, compact and efficient thermal energy reservoirs are described in which thin layers of a heat storage material, such as an inorganic salt having a high latent heat of fusion, are heated or cooled by an intermittent primary energy source, such as solar or off-peak electric power. The stored energy is utilized during periods when the primary energy source is not available. The heat storage material is contained in flat fluid tight packages, such as a heat sealed polyethylene film bag, which can readily be removed and replaced through removable panels or doors in the insulated reservoir enclosure.

Steady Metal Combustor as a Closed Thermal Energy Source

Abstract: A thermal energy source is described which can be used with closed thermodynamic cycles to obtain a power system that is independent of the environment. The energy source is based on the steady combustion of gaseous sulfur hexafluoride and liquid lithium, yielding liquid lithium fluoride and lithium sulfide as combustion products. For liquid bath temperatures between 1065 and 1638 K, lithium and the combustion products form an immiscible liquid mixture and the denser product liquid can be removed from the combustor through a trap in order to achieve steady operation. A combustor with a maximum thermal power of 25 kW was employed to study the operation of this system, to measure performance, and to determine the properties of the immiscible liquid mixture. The experiments also examined ignition characteristics, various modes of product collection, utilization of the reactants by the combustion process, and system capabilities for long term, variable-load operation as a thermal energy source. An analysis based on the van Laar thermodynamic model was developed which satisfactorily correlates both properties and the thermal performance of the system.

Processing of tar sands

Abstract: Petroliferous material of tar sands is processed to recover material boiling below 850° F. with higher boiling material converted to high BTU fuel gas and with heat developed transported to improve the thermal efficiency of the combination operation.

Gas turbine engine power plant using solar energy as a heat source

Abstract: The working medium of a gas turbine engine power plant is heated indirectly by energy derived by solar radiation, the power plant comprising radiant energy collecting means, radiant energy receiving means, radiant energy heat transfer means, a relatively large capacity pressurized heat store and a gas turbine engine in which the compressed air is heated by heat energy in the heat store.

Parametric simulation of significant design and operating alternatives affecting the fuel economy and emissions of spark-ignited engines

Abstract: A fundamental thermodynamic model of the complete spark-ignited, homogeneous charge engine cycle has been used in several parametric analyses to predict the effects of engine design and operating alternatives on fuel consumption and emissions of NOx and unburned hydrocarbons (HC). The simulation includes sub-models for wall heat transfer, NOx and HC emissions, and the engine breathing processes. This work demonstrates the power and utility of a comprehensive engine simulation by presenting several independent parametric studies that were carried out in response to genuine engine design and/or operating strategy questions. Included in this compilation are the effects of cycle heat loss, exhaust port heat loss, combustion duration, and charge dilution (exhaust gas recirculation and/or lean air-fuel ratio). In addition, the influence of the design variables associated with bore-stroke ratio, intake and exhaust valve lift, and cam timing are considered. Actual engine data is shown to enhance and lend validity to the analytical results when appropriate.

Heating system producing warm air for motor vehicles driven by an internal combustion engine

Abstract: A warm-air heating system for motor vehicles driven by an internal combustion engine, which is equipped with a heat-exchanger adapted to be acted upon by atmospheric air for the transfer of heat from a heat carrier that circulates in a line circulatory system, and with a heat-exchanger also interconnected in the line circulatory system which absorbs exhaust gas heat of the internal combustion engine and gives off the heat to the heat carrier; the line circulatory system for the heat carrier of the heating system is thereby in heat-transferring connection at least with the lubricating oil circulatory system of the internal combustion engine.

Research on the sodium heat engine

Abstract: The Sodium Heat Engine (SHE) is a new device for direct thermoelectric energy conversion. It uses the ionically conducting ceramic, 5''-alumina, to form a high-temperature concentration cell for elemental sodium. The vapor pressure (activity) gradient across the cell is maintained by a high temperature heat source (at 600-1000/sup 0/C) on one side of a ..beta..-alumina membrane and a low temperature condenser (at 100-200/sup 0/C) on the other side Theoretical analysis of the SHE shows that under quasi-reversible conditions the efficiency should be more than 90% of Carnot efficiency. For typical operating conditions of T2=800/sup 0/C, T/sub 1//sub 2/-100/sup 0/C, a specific power output of 0.7 watt/cm/sup 2/ has been achieved in test electrodes. If certain design criteria involving parasitic heat losses can be met, the SHE should achieve overall thermal efficiency in the range of 20-40% at a power output of 1 watt/cm/sup 2/. 7 references, 11 figures.

Efficiency of the solid‐state engine made with Nitinol memory material

Abstract: The thermal efficiency of the solid‐state engine (SSE) based on the shape‐recovery phenomenon accompanied by the martensite‐parent‐phase (M→P) transformation has been evaluated. Particular application is made for the memory components made with the Nitinol alloys. The result is expressed in terms of the hot and cold reservoir temperatures (T and T0), the latent heat of the M→P transformation, ΔH, the fraction of the M→P transformation, α, and a coefficient β that depends on the geometry and type of the deformation of the memory component. The relationship between the efficiencies of the SS and the Carnot engines is discussed. The factor α is expressed in terms of Tc, the critical temperature under an applied load, the degree of prestraining of the component, and the volume change involved in the M→P transformation. It is seen that the maximum of the thermal efficiency approaches that of the Carnot engine at an x=T−T0 value that depends on T0, ΔH, and α. Choosing T0=297 K and a Nitinol alloy with ΔH=2 cal/g, the maximum efficiency, about 20%, occurs at x=75 K. Moreover, for a steady‐state heat‐mechanical energy conversion, the critical temperature of the memory component is found in terms of the T and T0 temperatures. The engine efficiency in terms of the energy loss due to friction and the heat‐transfer coefficient is analyzed and estimated to be about 16%. It is seen that higher thermal efficiency can be obtained if a Nitinol alloy with a larger H value than given above can be found.

The efficiencies of thermochemical energy transfer

Abstract: A general thermodynamic study of thermochemical energy transfer and work production processes is presented. Both gaseous systems in which the effluent of each reactor is not separated into the reactant and product species, and liquid/gas systems in which the effluent separates spontaneously into liquid and gas phases, are treated. the study extends to consideration of non-isothermal reactors, to the individual roles of reactor and heat exchanger in the work production processes and to the significance of the intrinsic work of phase separation. the overall system efficiency is derived as the product of two efficiencies: the energy storage efficiency which defines the fraction of the input energy passed in chemical form to storage and the work recovery efficiency which defines the fraction of this stored energy available as output work. the fundamental thermodynamic processes underlying the derivation of these efficiencies are examined from the point of view of optimization of the design and operation of individual system components. In particular, it is shown that the available work from a thermochemical energy transfer system approaches the maximum value given by the Gibbs' free energy change when the temperature profile of the exothermic reactor is suitably tailored. The work of separation has formed the basis of the analysis of specific system components and has given a useful insight into the understanding of energy storage efficiency. Work recovery efficiencies are calculated for the ammonia/hydrogen-nitrogen system and the paper concludes with a discussion of some practical considerations relating to the recovery of work and the performance that one might ultimately expect from this system.

Methods and means for storing energy

Abstract: A method is disclosed for storage of energy produced at a conventional power station and release of said energy when subsequently required. The method comprises using the energy to refrigerate and liquefy atmospheric nitrogen and oxygen, storing the liquid gases at substantially below atmospheric temperature and subsequently using cold liquid gas, in combination with a source of heat at or above atmospheric temperature, to drive a closed cycle heat engine and yield mechanical energy. Auxiliary open and closed cycle heat engines are added to yield further mechanical energy and so utilize the full energy potential of the cold liquid gases.

Combustion system with partial recirculation of exhaust gases and feed mechanism therefor

Abstract: A combustion system for particulate wood waste, coal, peat and other combustible materials is disclosed. The system comprises means for feeding combustion material into the combustion chamber of a furnace and means for recirculating a portion of the exhaust gases from the furnace back into the combustion chamber for increasing the temperature of the combustion chamber and so improve the thermal efficiency of the furnace.

Influence of cyclic wall-to-gas heat transfer in the cylinder of the valved hot-gas engine

Abstract: The valved hot-gas engine (VHGE), first reported at the 1973 IECEC is a closed regenerative, reciprocating Brayton cycle engine using helium as the working gas. Preliminary analysis shows that this engine is competitive with the Stirling engine in terms of low pollution, high efficiency, and power density. The low efficiencies of the first one cylinder engine have been under investigation since 1972. Tests and analyses show that cyclic heat transfer between the gas and the cylinder causes the major loss rather than piston ring leakage as first suspected. Engine efficiency could approach the expected 47% by further reduction of cyclic heat transfer in both the expander and the compressor.

Energy conversion method with water recovery

Abstract: A mechanical energy conversion method and system for the restoration of dissipated heat energy, contained in natural or artificial water bodies at or near ambient temperatures, to industrial process heat, mainly in the form of steam up to 200°-400° C. The sensible heat contained in a water body is concentrated as latent heat in low pressure water vapor which is thermo-compressed by steam ejection to an intermediate pressure level, wherefrom mechanical compression takes over, generating highly superheated output steam. The ejecting steam is not generated in a boiler, but is continuously regenerated by the compressor and routed back for repeated ejection. The compressor is driven by a heat engine whose reject heat is collected and upgraded as well. The output of heat energy is essentially equal to the sum of the heating value of the fuel consumed and the intake of latent heat and amounts thus to substantially more than the heating value of the fuel alone.

Steel mfr. from solid ferrous material esp. scrap, in converter - where bottom tuyeres are used as fuel burners to preheat charge prior to melting and oxygen refining

Abstract: In the lower part of the converter are tuyeres for injecting oxidising gas, esp. O2, surrounded by a protective medium and burnt with fuel (I) contg. carbon to produce hot combustion gas. The gas travels up the heap of scrap to preheat the latter, followed by melting and oxygen refining in the same converter. During preheating, fuels (I) are fed through a pipe and/or the tuyeres, which consist of at least two concentric pipes used as burners for preheating. The fuel is burnt to CO2 and H2O, and pref. consists of light or heavy oil; residue and/or tar from crude oil distn.; or CH4, C3H8, and/or C4H10. Preheating is pref. to max. 1100 degrees C using 1-10 l fuel/minute/tonne solid ferrous material. The pref converter contains tuyeres in the lower side walls and in a replaceable base. An inexpensive process for steel mfr. from scrap, prereduced pellets, sponge-or solid pig-iron, where a high amt. of scrap can be used with rapid melting, high thermal efficiency and long lining life.

Resonant or pulsating combustion heating apparatus

Abstract: A resonant or pulsating combustion heating apparatus of the present invention provides a high thermal efficiency heater with low concentrations of carbon monoxide and nitrogen oxides in the exhaust gas. The pulsation heater is constructed to provide an afterburner or late-combustion reactor in the pulsation tube. Combustion in the combustion chamber is of a relatively rich fuel/air mixture in which no nitrogen oxides are produced. The afterburning in the pulsation tube is carried out in the presence of excess air providing late combustion to remove carbon monoxide (CO).

Gas-powered engine adapted to utilize stored solar heat energy and compressed gas power system

Abstract: Atmospheric fluids such as air and water are used to increase the power output of a gas compressor-gas engine system. Compression is aided by yielding heat over ambient atmospheric temperature. Gas from the compressor drives a gas engine. The gas engine gains power by absorbing heat energy from ambient atmospheric fluid. The warmed fluids and cooled fluids of the system may be usefully applied.

Cooling system of gas turbine power generating equipment

Abstract: PURPOSE:Cooling system of gas turbine power generating equipment which is improved thermal efficiency of gas turbine to require cooling, by using generated steam from gas turbine exhaust heat for cooling source.

Method for converting heat energy to mechanical energy with monochlorotetrafluoroethane

Abstract: Monochlorotetrafluoroethane is useful as a power fluid with particular suitability for large scale Rankine cycle applications based on systems with moderate temperature heat sources. The fluid is utilized in a Rankine cycle application by vaporizing the fluid by passing the same in heat exchange relationship with a heat source and utilizing the kinetic energy of the resulting expanding vapors to perform work. In this manner heat energy is converted to mechanical energy.

Thermalldecomposition apparatus for solid waste

Abstract: PURPOSE:To provide a dangerless apparatus described in the title, which is of high thermal efficiency and is constituted of a retort. The retort has an inlet and an outlet at the both ends respectively and is made of straight, heat resistant, heat conductive material, and at least a part of which pierces through a fluidized bed in order to heat indirectly the material to be dry distilled in the fluidized bed of a heating chamber.

Composite heat pump system

Abstract: PURPOSE:To obtain a system enabling high thermal efficiency with a comparatively small mechanical power by combining both compression and absorption type heat pumps.

Apparatus for treating sludge

Abstract: PURPOSE:To improve combustion rate and thermal efficiency of the furnace, by extending an arc-electrode protecting tube, providing blowers respectively at an air inlet port and in an exhaust-gas outlet passage, and by an efficient use of waste heat