Showing papers on "Thermal efficiency published in 1975"

Efficiency of a Carnot engine at maximum power output

Abstract: The efficiency of a Carnot engine is treated for the case where the power output is limited by the rates of heat transfer to and from the working substance. It is shown that the efficiency, η, at maximum power output is given by the expression η = 1 − (T2/T1)1/2 where T1 and T2 are the respective temperatures of the heat source and heat sink. It is also shown that the efficiency of existing engines is well described by the above result.

Waste heat regenerating system

Abstract: The invention described herein pertains to a combination hydraulic thermodynamic prime mover, for the conversion of thermal energy from low-temperature heat sources, such as solar heat, geothermal steam of poor quality and waste heat of all kinds, into useful mechanical or electrical power, employing a new and novel technique of low temperature-pressure energy conversion.

Process for recovering energy from liquefied gases

Abstract: In a process for recovering the energy from a liquefied gas by evaporation in heat exchange with a cycle medium which is simultaneously cooled, said cycle medium being thereafter compressed, heated, subjected to engine expansion and recovered in a cyclical manner, wherein the improvement comprises operating the cycle so that the cycle medium remains in the gaseous phase throughout the entire cycle.

Hybrid motor unit with energy storage

Abstract: An automotive engine unit comprises an internal combustion engine adapted to meet the power requirements of a vehicle under steady speed running conditions, a hot air turbine unit of higher power output than the internal combustion engine adapted to meet the additional power requirements for accelerating the vehicle, an air compressor driven directly or indirectly by power supplied by the internal combustion engine, and an air storage reservoir. During acceleration of the vehicle, air from the reservoir is fed to the turbine through a heat exchanger where it absorbs heat from the exhaust gases of the internal combustion engine.

Intake-air amount detecting system for an internal combustion engine

Abstract: There is provided an intake-air amount detecting system for an internal combustion engine in which a first temperature of an intake air for an internal combustion engine is measured, the intake-air is heated by an electrical heating element, a second temperature of the heated intake-air is measured, an amount of heat generated by the electrical heating element is adjusted to maintain a difference between the second temperature and the first temperature at a fixed value, and the amount of heat generated by the heating element is calculated to determine the amount of the intake-air to the internal combustion engine.

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.

Computer analysis of Stirling engines

Abstract: The analysis given applies to reciprocating machines that are based on a regenerative thermal cycle. Included are closed-cycle Stirling engines, refrigerators and heat pumps, related free piston machines, cryogenerators, pressure generators, and Vuilleumier machines. Regenerative reciprocating gas machines are high-efficiency, open- or closed-cycle mechanisms either for converting heat energy into mechanical or pneumatic power, or alternatively for elevating heat energy to a higher temperature level through an expenditure of mechanical work or heat energy. Finally, they may perform several of these operations simultaneously. The computer program described realistically simulates the behavior and the characteristics of a regenerative closed-cycle machine, both in steady-state and transient operation. However, substantial programming effort and a large-scale digital computer, such as an IBM 360/65, were required. Output from the program included both parametric variations and single-valued characteristic criteria (run/no run condition, efficiencies, specific output, etc.). The program structure allows planned parametric studies for developing a superior machine. Either an intuitive trial-and-error approach or a sophisticated system transfer function analysis can be used to describe frequency responses of the principal output parameters as a function of variations in the design parameters.

Means of increasing efficiency of CPC solar energy collector

Abstract: A device is provided for improving the thermal efficiency of a cylindrical radiant energy collector. A channel is placed next to and in close proximity to the nonreflective side of an energy reflective wall of a cylindrical collector. A coolant is piped through the channel and removes a portion of the nonreflective energy incident on the wall which is absorbed by the wall. The energy transferred to the coolant may be utilized in a useful manner.

Single mixed gas type gasoline engine

Abstract: PURPOSE: A single mixed gas type gasoline engine, that realizes to promote thermal efficiency by increasing combustion velocity while providing injection port direction installed in a sub-combustion chamber of a partial spherical crust state to pass vicinity of central part of an intake valve and an exhaust valve head and a skittish area to short cut flame propagation distance. COPYRIGHT: (C)1977,JPO&Japio

Method and system for utilizing waste energy from internal combustion engines as ancillary power

Abstract: A system for increasing the efficiency of an internal combustion engine by converting the waste energy to drive a turbine. Output power from the turbine is used to supplement the basic power of the engine or to provide power to auxiliary systems such as the electrical generator, compressor type air conditioner, power assist steering mechanism and power assist brakes. In a disclosed embodiment, a thermostatically actuated valve is responsive to heat build-up in the engine to direct a stream of water on a water based liquid from a reserve tank into a steam generating chamber utilizing the waste heat of the engine where it is converted to high pressure steam which drives a turbine. The turbine shaft is mechanically coupled to supplement the power of the engine and/or to provide power to one or more of the auxiliary systems mentioned above through a series of jackshaft attachments.

Irreversibility, entropy production, and thermal efficiency

Abstract: The relationships between the entropy production per cycle and the thermal efficiency are investigated for a class of irreversible cyclic processes. Examples are given that pinpoint specific sources of irreversibility and their thermodynamic consequences. It is found that an increase (decrease) in an irreversible cycle’s thermal efficiency does not necessarily lead to a decrease (increase) in its entropy production even if the work done per cycle is held constant. Only for the case of a reversible Carnot cycle is it guaranteed that a change (negative for this case) in the efficiency is met by an entropy production change of opposite algebraic sign. Sufficiency conditions are found for which the entropy production and the efficiency η are inversely related for more general cyclic processes. For a given set of heat reservoirs and specified values of the work output W, the absolute minimum and maximum entropy productions are determined and are shown to be monotonically decreasing functions of η for fixed W. It is shown also that, for an irreversible cycle with maximum and minimum temperatures T+ and T−, respectively, η? (1−T−/T+)(1+T−ΔS/W)−1, where ΔS is the entropy production per cycle. The equality holds only for a cycle employing two reservoirs. The potential relevance of these results to environmental and technological problems is mentioned.

Isothermal open cycle thermodynamic engine and method

Abstract: A pollution-free thermodynamic engine system and method for converting thermal potential energy to useful mechanical energy employing an isothermal or quasi-isothermal primary working fluid thermodynamic expansion cycle. A relatively cold primary working fluid is conducted from a low temperature storage tank, through a plurality of engine stages each comprising a heat exchanger and an expansion engine operated on an isothermal of quasi-isothermal expansion cycle, and finally exhausted. A relatively warm secondary fluid is circulated through the engine stages to provide a heat input thereto. The engine stages are connected to the primary working fluid path in parallel to operate on a first isothermal expansion cycle; the engine stages are cascaded to operate on a second serial isothermal expansion cycle. A plurality of preliminary heat exchangers in the primary fluid loop enable operation of the engine system on an alternate quasi-isothermal cycle in which the primary working fluid is cycled a plurality of times in a closed loop to improve the energy conversion efficiency of the system.

System for utilizing waste heat of an internal combustion engine

Abstract: Waste heat generated by an internal combustion engine is utilized by an apparatus comprising a supercharger, a turbine drivably engaging the supercharger, a vaporizer, a condenser and fluid injection duct means. The turbine, the vaporizer and the condenser form a closed loop within which a motive fluid is circulated. The vaporizer is intimately associated with the internal combustion engine, and the motive fluid within the vaporizer is converted to gaseous form by heat transfer from the engine. The vaporized fluid is then used to drive the turbine which, in turn, drives the supercharger, thereby increasing the efficiency of the engine. Spent motive fluid is recovered from the turbine, condensed, and recycled to the vaporizer. Additionally, a fluid injection duct introduces fluid preferably in the form of steam into the air which enters the engine.

Efficiencies of electrolytic and thermochemical hydrogen production

Abstract: Two methods not involving fossil fuels for manufacturing hydrogen have been suggested as a basis for an eventual hydrogen economy: first, electrolysis of water using nuclear (or ultimately solar, geothermal or thermonuclear) electricity and, second, thermochemical cycles using nuclear heat, in general from a high temperature reactor2,3. In the thermochemical processes, a series of chemical steps is envisaged that will allow the differential splitting of the H2O molecule by means of reactions at different temperatures and with appropriate thermodynamic requirements to give high efficiency. The sequence of reactions, ideally of gas–solid type, acts as an adsorption–desorption-cycle heat engine. For economic hydrogen production, high thermal efficiency combined with low capital investment cost is necessary. The question is whether a system constructed on the basis of a sequence of chemical reactions will be more efficient (and ultimately less costly) than one based on a heat engine producing electricity, followed by electrolysis. Here I shall examine briefly some aspects of the efficiency of both approaches.

Electric power generating device fed with energy recovered from the exhaust gases of an internal combustion engine

Abstract: An electric power generating device recovering the energy of the exhaust gases of an internal combustion engine, comprising a speed-reducer mounted between the engine and a transmission shaft and a turbo-alternator set driven by the energy taken from said exhaust gases and the turbine of which is operatively connected to said reducer through a reversible transmission system with variable speed keyed in follow-up relationship to the speed variations of said transmission shaft.

Thermodynamics of a simple rubber‐band heat engine

Abstract: We analyze the thermodynamics of a simple heat engine. The engine’s efficiency is calculated for an idealized but reasonable model. The engine’s work cycle is compared with a Carnot cycle, and it is shown to be equivalent to the Carnot cycle as an extremely ideal limiting case. A working model of the engine is easily constructed for classroom demonstrations. We measured the force law parameters for a working model, and we estimate the efficiency of this model. The estimated efficiency of our demonstration engine is small compared with that of a Carnot engine operating at the same temperatures. We show that a Carnot engine could in principle be constructed based on the thermal expansion concept, but its efficiency would be intrinsically small when rubber is the working substance because of the inherently small incremental temperature increase possible in an adiabatic expansion.

Maximum efficiency of direct utilization of radiation

Abstract: The author considers the thermodynamic efficiency limits associated with the direct conversion of solar energy into work (e.g., the photoelectric effect).

Efficient thermo-mechanical generation of electricity from the heat of radioisotopes

Abstract: The thermomechanical generator uses a thermomechanical oscillator to convert heat efficiently into a mechanical oscillation which in turn excites a suitable transducer to generate alternating electricity The thermomechanical oscillator used is based on the Stirling cycle, but avoids the need for rotary motion and for sliding pistons by having a mechanically-resonant, spring- suspended displacer, and by using an oscillating metal diaphragm to provide the mechanical output The diaphragm drives an alternator consisting of a spring- suspended permanent magnet oscillating between fixed pole pieces which carry the electrical power output windings Because a thermomechanical generator is much more efficient than a thermo-electric generator at comparable temperatures, it is particularly suitable for use with a radioisotope heat source The amounts of radioisotope and of shielding required are both greatly reduced A machine heated by radioisotopes and delivering 107W ac at 80Hz began operating in October, 1974 Operating experience with this machine is reported, and these results, together with those obtained with higher-powered machines heated by other means, are used to calculate characteristics and performance of thermo- mechanical radioisotope generators capable of using heat sources such as the waste-management $sup 90$Sr radioisotope sources becoming available from the US nuclear waste management programme Amore » design to use one of these heat sources in a 52-W underwater generator is described (auth)« less

Room heating apparatus using combustion

Abstract: Room heating apparatus having a burner disposed in the upper part of a body to which air for combustion is forcibly supplied from a blower, a heat exchanger and a combustion chamber serially connected below the burner, and a second blower for recycling air from the room over the outer surfaces of the heat exchanger and the combustion chamber being disposed in the bottom of the body. The combustion chamber and the heat exchanger are substantially flat-shaped in configuration being on the order of ten times their thickness in both height and width. Accordingly, the room heating apparatus is a compact heating unit having high thermal efficiency, and the blower for recycling air can be protected from damage due to heat of the burner, even in the event the blower is accidentally stopped.

Torch ignited engine

Abstract: PURPOSE:To improve the thermal efficiency of a torch ignition type engine by reducing the combustion time in the main chamber by setting the communicating port from the torch comes out in such a position that the volume of initial combustion of mixed air in the main chamber is maximized.

Precise combustion-control saves fuel and power

Abstract: Instrumentation assuring a minimum amount of excess air for combustion of fuels improves the importance and increases the thermal efficiency of boilers, furnaces, and kilns. This has now become an important factor due to increased fuel prices. To achieve good combustion control and the best fuel-burning efficiency requires that two fundamental conditions be established: exact balancing of the air/fuel ratio from burner to burner; and precise control of the chemical composition of the flue gases leaving the boiler or process. Three examples are given that illustrate the savings in detail. Calculations are given for a power-topping boiler in a pulp and paper mill generating 800,000 lb/h steam at 600 psi and 900/sup 0/F. The boiler includes an economizer and a small air heater. The second example is for an oil or coal fired rotary cement kiln that handles 100 tons/h of clinker. A third example is given for a gas-fired glass-melting furnace with a capacity of 11 tons/h of melt. (MCW)

Integral heater thermal energy storage device

Abstract: In a Vuilleumier cryogenic refrigerating system for operation wherein the source of thermal energy for the hot cylinder during periods of interrupted electrical energy is supplied by heat of fusion of the thermal energy storage material, the container for the thermal energy storage material is made the electrical heating element for both the refrigerator and the thermal energy storage material.

Enthalpy augmentation to MHD generation

Abstract: An improved magnetohydrodynamic (MHD) generator is provided by increasing the electrical conductivity of the working fluid by raising the temperature of the fluid. This is accomplished by providing an additional source of heat for the combustion products within the combustor. The additional source of heat in the combustor is provided by an electrical arc discharge within the combustor. The arc is energized by feeding back a part of the electrical output power from the MHD generator to the arc electrodes. In a typical nominal 20 megawatt system the thermal efficiency of the system is typically increased from approximately 20% to approximately 24.5% by such enthalpy augmentation.