Showing papers on "Thermal efficiency published in 1979"

The quantum open system as a model of the heat engine

Abstract: The quantum open system weakly coupled to thermal reservoirs at different temperatures and under the influence of slowly varying external conditions is studied. The famous Carnot inequality for the efficiency of any heat engine is obtained.

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.

Evaluation of combined photovoltaic/thermal collectors

Abstract: The thermal and electric performance of an air and a liquid type combined photovoltaic/thermal solar collector has been evaluated, yielding close correlation with theoretical results. Maximum thermal efficiencies of 42.5% and 40% for the liquid and air collectors without electric power production decreased to 40.4% and 32.9% when electrical power was produced. Maximum electrical efficiencies of 6.8% were measured.

Process for wastewater treatment and wastewater sludge conversion into energy

Abstract: The process disclosed includes treating settled sludge and/or organic debris recovered from a wastewater treatment system and thermally converting the treated material and/or comminuted organic solid wastes separately or in combination into steam combustible gas, residual tars and oils and other energy by-products which are recycled as heat for increasing the thermodynamic efficiency of the process. The process further includes cleaning the combustible gas which is provided during the thermal conversion so that the gas is suitable for driving gas engine or gas turbine generators and the like.

How to Estimate Recoverable Heat Energy in Wood or Bark Fuels.

Abstract: : A reference source is provided for estimating the amount of heat energy that may be recovered using wood or bark fuel in typical furnace and boiler or hot air combustion heat recovery systems A survey of reported data on higher heating values for various species of wood and bark fuels is provided A set of formulas of a type commonly used by combustion technologists is also provided for estimating combustion system heat losses and net recoverable heat energy per pound of fuel as-fired, based on fuel higher heating value, moisture content, and excess air, stack gas temperature, and ambient temperature assumptions (Author)

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.

Energy conversion method and system

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 sun 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.

Moving bed heat storage and recovery system

Abstract: An energy storage and recovery system designed for storing excess over demand energy generated by a steam cycle electrical generating plant during slack electricity demand periods and for recovering the stored energy to provide supplemental electricity during peak demand periods. The system utilizes one or more moving bed heat exchangers for transferring heat between the steam cycle of the power plant and a moving bed of refractory particles. Pipes and valves establish fluid communication between the heat exchangers and the steam cycle to supply fluid to selectively heat the moving bed of refractory particles or to cool them as the case may be. One or more insulated silos are provided for storing the refractory particles and means are provided for transporting the particles between the silos and the heat exchangers.

Internal combustion engine with gas synthesizer

Abstract: An internal combustion engine, synthesizing CO and H2 fuels from methanol in a first synthesizer, and also synthesizing H2 fuel from CO and water in a second synthesizer, thus upgrading a technically difficult to use fuel to a low polluting, easily usable fuel, by use of the energy from exhaust gas waste heat thus improving the fuel heating value by 20%; the engine fuel system also having an alternate energy source for synthesizing the fuel, the engine also having an additional alternate fuel source for engine starting and operation when the synthesized fuel reservoir is low and electrical battery energy is limited thus allowing time for the heat exchanger synthesizers to warm up to produce CO and H2 fuel, which is especially required during cold operating seasons.

Cooling and heating system utilizing solar heat

Abstract: A cooling and heating system utilizing solar heat comprises a heat collector for heating a circulating heat medium with solar heat, an absorption refrigerator operable with the heat medium heated by the heat collector and serving as a generating heat source to provide a chilled medium, and an air-conditioning unit for circulating the chilled medium or the heated medium alternatively therethrough to cool or heat the space to be air-conditioned. The system further comprises a bypass line provided with an auxiliary refrigerator of the dual-effect type and connected to an intermediate portion of a line extending from the absorption refrigerator to the air-conditioning unit for supplying chilled medium or the heated medium to the unit. Change-over means is provided for passing the chilled medium or the heated medium through the bypass line.

Heating system and method utilizing recoverable engine heat

Abstract: A heating system and method are provided in which a defined area to be heated or to be used for drying crop material may be connected through adjustable ducting to either a primary heat source, such as an oil or gas furnace, or to an alternate heat source comprising a shrouded engine, such as an internal combustion or turbine engine, from which heat may be extracted. A control system allows the engine heat source to be automatically activated in the event of an electric power failure or to be selectively used as the sole source or as a supplementary back up source of heat. The control system further allows the automatic activation of the electric system, should the engine system fail, thus cycling from one mode to the other when either is selected as the primary mode.

Evaluation of acetylene as a spark ignition engine fuel

Abstract: In spite of its known shortcomings as a fuel for spark ignition engines, acetylene has been suggested as a possible alternative to petroleum-based fuels since it can be produced from non-petroleum resources (coal, limestone and water). Therefore, acetylene was evaluated in a single-cylinder engine to investigate performance and emission characteristics with special emphasis on lean operation for NOx control. Testing was carried out at constant speed, constant airflow and MBT spark timing. Equivalence ratio and compression ratio were the primary variables. The engine operated much leaner when fuelled with acetylene than with gasoline. With acetylene, the engine operated at equivalence ratios as lean as 0·53 and 0·43 for compression ratios of 4 and 6, respectively. However, the operating range was very limited. Knock-induced preignition occurred either with compression ratios above 6 or with mixtures richer than 0·69 equivalence ratio. Both the indicated thermal efficiency and power output were less for acetylene fuelling than for gasoline. Acetylene combustion occurred at sufficiently lean equivalence ratios to produce very low NOx and CO emissions. However, when the low NOx levels were achieved hydrocarbon control was not improved over that with gasoline. Despite the potential for NOx control demonstrated in this study of acetylene fuelling, difficulties encountered with engine knock and preignition plus well-known safety problems (wide flammability limits and explosive decomposition) associated with acetylene render this fuel impractical for spark ignition engines.

Analysis of a heat exchanger-thermoelectric generator system

Abstract: Analysis of a thermoelectric generator (TEG) in an ocean thermal energy conversion (OTEC) application is presented. An analytic model is developed for describing the heat exchanger-TEG interactions. This model is used to illustrate limitations of applying conventional fixed junction temperature assumptions to systems experiencing significant temperature drops across the heat exchanger surfaces. Design methods are developed for determining the thermoelectric element geometry that produces maximum output power. Results show that a heat exchanger-TEG system may deliver about 100 W/m/sup 2/ of heat exchanger surface. This compares favorably with conventional OTEC schemes.

Metallurgical problems and opportunities in coal-fired steam power plants

Abstract: External constraints on the generation of electricity in steam power plants that determine metallurgical research and development include 1) the source of fuel, 2) environmental controls, 3) the economy of scale, 4) efficiency of energy conversion, and 5) reliability of the power generating equipment. These are reviewed in the current time frame. Economic and political factors dictate that coal and nuclear fission are the major fuels for generation of electricity until the end of the century. Environmental constraints on SO2 emission dominate a great deal of current materials research and development. Only a small percentage of available coal is low enough in sulfur to meet new source standards. Conversion of coal to a clean gaseous, liquid, or solid fuel is replete with difficult metallurgical problems, chiefly in high temperature corrosion. To compete with stack gas desulfurization it is necessary to burn the clean converted coal in more thermally efficient combined cycles, which requires development of high temperature industrial gas turbines. The fabrication problems of advanced air or water cooling of metal hot components are traded off against the brittle design problems of ceramic components. Removal of sulfur in the combustion stage in fluidized beds containing an SO2 acceptor has many attractive features, but potential problems exist in hot corrosion of the in-bed tubes and erosioncorrosion-fouling of expander turbines. The economy of scale has increased power plant size to about 1200 MW, where further increases seem to have stalled because of metallurgical problems. Improvements in thermal efficiency from high steam temperatures and pressures also have stalled, and even retreated, because of metallurgical barriers. The main current effort in materials research and development is aimed at improved reliability rather than efficiency. Two metallurgical opportunities to improve reliability are described in detail: titanium low pressure turbine blades and large rotor forgings.

Liquid-phase methanol. Final report

Abstract: The key to a new process on methanol synthesis is a three phase fluidized system. An inert liquid is used as a sink for the exotherm of the synthesis reaction. This temperature control feature allows greater per pass conversion and improved thermal efficiency as compared to presently available technology. The first annual report presents experimental findings from a bench scale apparatus. Thermodynamic calculations and a preliminary economic analysis are presented. The interest in this technology is twofold. One is in its potential as an efficient method of energy storage from coal-based gasification power plants. This would allow a gasifier to run at constant throughput, maximizing its efficiency, while demand fluctuations on the utility side can be followed by inventory changes in the energy storage system. The other application is in a plant to produce fuel grade methanol for export to power plants for intermediate or peak load use. (GRA)

High efficiency furnace

Abstract: A heat exchanger and process having multiple fluidized beds for heat exchange between two gas streams of different temperatures. The apparatus and process provides a compact high efficiency warm air furnace especially adapted for energy conservation for the heating of modern highly insulated residential buildings by gas fired furnaces of relatively low rated gas input.

Heating system with heat pump and auxiliary heater

Abstract: A heating system for a building utilizing a heat pump having a condenser which is driven by an internal combustion engine. The internal combustion engine drives an additional aggregate, such as a brake, for the purpose of generating additional heat which is added to the main heat carrier in the heating network in the building. The circulating system for the additional heat generating aggregate is self-contained and separate from the heating network of the building.

Second-law analysis of solar-thermal processes

Abstract: The second law of thermodynamics provides an analytic framework for the assessment of the potential displacement of fossil fuels by solar energy. the most promising areas are those which have entropy levels corresponding to the entropy level of the solar resource as converted to heat in various types of solar collectors. Since the entropy of solar heat can be partitioned by the means of collection—d.g., by the collector concentration ratio—solar can be matched much more precisely to many tasks at temperatures up to 300°C than can fossil fuels which are low entropy sources now widely misused for high entropy tasks.

Recyclable-fuel engine system

Abstract: A recyclable-fuel engine system designed for use in a vehicle. The system includes a hydrogen-producing catalytic unit having plural catalytic beds, and a hydrogen-fueled engine having combustion and exhaust chambers. The catalytic beds, when supplied with heat, catalyze a reduced form of a hydrocarbon carrier to hydrogen and a dehydrogenated form of the carrier. One of the catalytic beds is supplied heat by direct heat transfer from the engine's exhaust chamber. The remaining catalytic beds are supplied heat by heat pipes receiving heat from the combustion and exhaust chambers. The hydrogen produced in the catalytic unit is supplied to the engine, to power the same. Also disclosed herein are apparatus and method for regenerating the catalytic beds periodically.

Thermoclines: A Solar Thermal Energy Resource for Enhanced Hydroelectric Power Production

Abstract: The solar thermal energy stored in hydroelectric reservoir thermoclines is very large and greatly exceeds the gravitational hydroenergy of the surface water, even after limitations arising from the second law of thermodynamics have been taken into account. Greatly enhanced power production can be obtained at present hydroelectric facilities if heat engines are adapted to exploit this large thermal energy resource.

Feedback energy conversion system

Abstract: A heat pumping process for the generation of industrially useful heat energy achieves an improved fuel effectiveness by feeding back to the process part of its otherwise output heat energy as an input to assist in compressing the process evaporized performing fluid. An equivalent amount of extraneous fuel otherwise required to carry out the mechanical work now done by the fed back energy is thus replaced.

Analysis of pollutant formation and control and fuel economy in diesel engines

Abstract: Publisher Summary This chapter presents a comparison between the characteristics of the diesel and other automobile engines. The high thermal efficiency of the diesel engine is mainly caused by the relatively high compression ratio required to start the autoignition process, the lower pumping losses as a result of the absence of the throttle valve, and the overall lean mixture required to achieve an efficient heterogeneous combustion process. The chapter describes high speed diesel engines used for automotive applications. Pollutants from the automotive power plants are found to be a major contributor of the photochemical smog formation in the atmosphere and a cause of social and health problems. The preignition processes in diesel engines may be divided into physical and chemical processes. The physical processes include spray disintegration and droplet formation; heating of the liquid fuel and evaporation; and diffusion of the vapor into the air to form a combustible mixture. The chemical processes include the decomposition of the heavy hydrocarbons into lighter components and the preignition chemical reactions between the decomposed components and oxygen.

Energy efficient heat-treating furnace system

Abstract: A method and apparatus are disclosed for heat-treating parts in a furnace system which uses a minimum total amount of energy. The self-contained, continuous heat-treating system includes components such as a carburizer, a tempering furnace, and a part cooler. Energy transfer between these and other components operable at different temperatures and/or energy requirements are used to maximize thermal efficiency of the system. Furnace components are provided and interconnected so that combustion air for radiant tube heaters supplying thermal energy to parts in a high temperature furnace such as a carburizer is preheated by exchanging heat in a part cooler and by recuperation of the carburizer exhaust; combustion products from the carburizer supply energy for reheating parts in a lower temperature furnace such as a tempering furnace; the tempering furnace exhaust is used for preheating parts prior to their entry into the carburizer; and energy transferred by the parts to a quench medium is used to heat water for subsequent washing of the parts. In one arrangement of components a tempering furnace is mounted on top of a carburizer as part of a compact multi-level configuration. In another arrangement the components form a single level system with energy transfer features and high thermal efficiencies similar to those of the multi-level system.