Showing papers on "Thermal efficiency published in 1981"

Finite time optimizations of a Newton’s law Carnot cycle

Abstract: We treat the problem of optimal finite time operations of a heat engine using an arbitrary working fluid and working between two constant temperature heat reservoirs. We work in a simplified framework (’’Newton’s law thermodynamics’’) which considers only losses associated with the heat exchange processes. We find the operations which maximize power, efficiency, effectiveness, and profit and those which minimize the loss of available work and the production of entropy. We find that all these optimal operations take place with the working fluid exchanging heat at a constant rate with each reservoir (implying a constant rate of entropy production) and undergoing adiabatic processes instantaneously. We define ’’Carnot space’’ to be the set of all operations of the engine which consist of constant rate heat exchanges and instantaneous adiabats. All optimal operations are points in this space which is shown (within the model) to be three dimensional. The different optimal operations with different connotations of ’’optimal’’ as described above are compared within this framework. To further study the economic implication of this model we also view the operation of the engine as an economic production process with work as its output. We obtain a simple analytical form of the production function and see repeatedly that maximum profit operation is a compromise between operation which maximizes the power and operation which minimizes the loss of available work. The path of maximum profit is obtained as a function of the costs of power and of availability.

On the thermodynamic limit of photovoltaic energy conversion

Abstract: An infinite stack ofp—n junctions with smoothly varying bandgap from ∞ to 0 is considered. AnI —V characteristic is derived, which is more correct than the classical exponential characteristic. It is shown that open-circuit operation is a reversible process and leads to the Carnot efficiency, if one defines the efficiency in the way that is usual in the theory of thermodynamic engines. If instead one uses the definition of efficiency usual in photovoltaics, open-circuit mode gives rise to zero efficiency. Then operation at maximum efficiency equals operation at maximum power and is not reversible.

Maximum work from a finite reservoir by sequential Carnot cycles

Abstract: The production of work from a heat source with finite heat capacity is discussed. We examine the conversion of heat from such a source first by a single Carnot engine and then by a sequence of Carnot engines. The optimum values of the operating temperatures of these engines are calculated. The work production and efficiency of a sequence with an arbitrary number of engines is derived, and it is shown that the maximum available work can be extracted only when the number of cycles in the sequence becomes infinite. The results illustrate the importance of recovery or bottoming processes in the optimization of work‐producing systems. In addition, the present model illuminates one practical limitation of the Carnot cycle: The Carnot efficiency is only obtainable from a heat source with infinite heat capacity. However, another cycle, somewhat reminiscent of the Otto and Brayton cycles, is derived which will provide the maximum efficiency for a heat source with a finite heat capacity.

Balancing the heat flow between components associated with a gas turbine engine

Abstract: Heat transfer systems for maintaining a thermal balance between a gas turbine engine and heat generating accessory components of the engine are disclosed. In the embodiment illustrated, heat is removed from the cooling system 48 of an electrical generator 46 and is transferred to the fuel supply system 32 of the engine. In one detailed embodiment, the cooling system 48 is in direct heat transfer communication with the downstream portion 62 of the fuel supply system through a heat exchanger 76 and in indirect heat transfer communication with the upstream portion 60 of the fuel supply system through the fuel recirculation system 42.

Effects of dust on the performance of thermal and photovoltaic flat plate collectors in Saudi Arabia: preliminary results

Abstract: The effect of dust accumulation on the surfaces of flat plate thermal and photovoltaic collectors has been studied and preliminary results are presented. One photovoltaic and two thermal panels were tested and the degradation in performance due to surface dust was determined. 10 refs.

Liquid Droplet Radiators for Heat Rejection in Space

Abstract: A radiator for heat rejection in space is described which utilizes a stream of liquid droplets to radiate waste heat. The large surface area per mass makes the liquid droplet radiator at least an order of magnitude lighter than tube and fin radiators. Generation and collection of the droplets, as well as heat transfer to the liquid, can be achieved with modest extensions of conventional technology. Low vapor pressure liquids are available which cover a radiating temperature range 250-1000 K with negligible evaporation losses. The droplet radiator may be employed for a wide range of heat rejection applications in space. Three applications - heat rejection for a high temperature Rankine cycle, cooling of photovoltaic cells, and low temperature heat rejection for refrigeration in space illustrate the versatility of the radiator.

Infrared emissions from turbofans with high aspect ratio nozzles

Abstract: A mixed flow turbofan is analyzed from the point of view of i.r. emission characteristics. A simple absorption coefficient model of the core flow gas displays the potential effectiveness of high aspect ratio nozzles as a variable in the design of aircraft engine installations for low i.r. signature. The simplicity of the model described and the limited view perspectives used to assess the signature restrict the usefulness of the results to that of guiding preliminary design. In general, more precise solutions are complex and depend on specification of a relatively large number of independent variables to describe the source—seeker geometry, weather, etc. The level of effort to carry out more accurate analysis may be inconsistent with the preliminary design process where simple criteria such as those described here may be sufficient to select the best of several candidate designs. The influence of cycle parameters is assessed using an /zth power dependence of radiation on temperature and a simple mixing model to estimate the core length. The analysis shows that cycle parameters which improve cycle efficiency and thus fuel consumption also reduce i.r. emissions. Bypass ratio near unity gives low i.r. signature for both optically thin and thick spectral regions.

Method of recovering waste heat from furnace flue gases using a granular heat exchange means

Abstract: Granular heat exchange medium is employed to recover waste heat from a combustion furnace, particularly a glass melting furnace, and the heated medium is then employed to pre-heat combustion air entering the furnace. A bed of granular heat exchange medium also may remove particulate emissions from the exhaust gas.

Method and apparatus for utilizing the waste heat energy of an internal combustion engine

Abstract: A method and apparatus for utilizing the waste heat energy of an internal combustion engine in which a turbine is driven by the exhaust gases from the engine and drives an electrical generator In order to permit a direct coupling between the turbine and the generator and to utilize completely the electrical energy recoverable from the waste heat energy, the generator is a synchronous machine with a non-wound rotor, the generator being connected via an electrical converter to an electric motor which is drivingly coupled to the internal combustion engine to relieve the load therein

Method and apparatus for reducing the initial start-up and subsequent stabilization period losses, for increasing the usable power and for improving the controllability of a thermal power plant

Abstract: In a method for reducing the start-up and stabilization period losses, for increasing the usable power and to improve the controllability of a thermal power plant, there are integrated into the power plant's steam cycle pressurized heat storage reservoirs which are charged by feeding them with excess heat produced in the said power plant as, for example, during the start-up and load stabilizing periods or during periods of reduced electrical power production and, when there is an increased demand for heat, the said heat storage reservoirs are discharged by the release of stored heat into the water-steam cycle. Control deviations in the electrical power while the power plant is in full operation are counterbalanced by changes in the charging and discharging streams of the pressurized heat storage reservoirs. In the apparatus for carrying out this method, pressurized heat storage reservoirs are connected, on the water-side, to the condensate system and, on the steam side, to the medium pressure of intermediate superheater network of the steam cycle or also to the power plant's medium pressure or low pressure turbine extraction points.

Catalytic gas-fired furnace system and method

Abstract: A gas-fired, forced air furnace system employing a fiber matrix burner element and a condensing-type heat exchanger to achieve both high system thermal efficiency and low emission of NO X and other gaseous pollutants The value of excess air in the fuel-air reactants supplied to the ceramic fiber matrix burner is selected to be equal to or greater than ten percent to provide NO X emissions below fifteen ppm on an air-free basis, with CO and HC emissions substantially comparable to those from existing furnaces, and the surface area of the condensing portion of the heat exchanger system is designed to produce sufficient condensation of moisture in the combustion gasses to produce an overall system thermal efficiency of at least about ninety percent

Locomotive energy recovery system

Abstract: An energy recovery system for a diesel electric locomotive is disclosed. The energy recovery system captures and stores the waste heat generated by the diesel engine of the diesel electric locomotive for use at a remote location at a later time. The energy recovery system also converts the electricity generated by the diesel electric locomotive during dynamic braking into heat, and captures and stores this heat for use at a remote location at a later time.

Apparatus for insuring the complete burning of fuel in a six cycle combustion engine

Abstract: A six cycle combustion engine is disclosed which utilizes the 5th and 6th cycle for drawing in and expelling preheated air to further warm the combustion chamber. The flow of the coolant water has been reversed so that heat absorbed in the engine head will flow to the cylinder walls and give a warming trend thereto. In addition, a fuel system is disclosed which insures the complete mixing of air and fuel vapor molecules prior to their deliverance to the intake of the engine.

Study of the methanol-reformed gas engine

Abstract: Methanol reacts in the presence of a catalyst and decomposes into a gas made up of hydrogen, carbon monoxide, etc. This is an endothermic reaction, hence the calorific value of the fuel increases. An experiment was conducted on the characteristics of an Otto cycle engine using reformed gas and methanol as fuels. As a result, it was confirmed that the engine provided high thermal efficiency and clean exhaust characteristics at a compression ratio of 14.0 and an excess air ratio of 1.7.

Can magnetic refrigerators liquefy hydrogen at high efficiency

Abstract: A concept for a hydrogen liquefier based on the magnetocaloric effect is introduced A second-law analysis of the general device is described The calculation predicts that efficiencies approx 50% of Carnot are probable A brief comparison to gas refrigeration systems is made

Process for cleaning surfaces fouled by deposits resulting from combustion of carbon-bearing substances

Abstract: A process for cleaning surfaces of installations fouled by products of combustion of carbon-bearing materials, such as in particular boiler combustion chambers, rotary or static heat exchangers, combustion product ducts and flues, electrostatic filters, etc., which are to be cleaned without having to stop the combustion process, in order to maintain maximum thermal efficiency in order thereby to make a substantial energy saving, in which an aqueous solution of ammonium nitrate and potassium nitrate is injected into the installation, the deposited substances being detached from the installation by means of sound sources.

Unitary heat engine/heat pump system

Abstract: A system for providing thermal energy output at intermediate levels below about 120° C. uses both a conventional heat source input and an ambient heat source input to the hot and cold ends, respectively, of a Vuilleumier cycle machine. While converting thermal energy to work in both a heat engine process and a heat pump process, an intermediate working chamber integral with both processes is arranged to provide thermal output at the desired intermediate level. By maintaining the pressure ratio within predetermined limits and observing a number of temperature relationships desirably high coefficients of performance are provided with useful levels of output in a reliable system having long operating life.

Solid fuel prodn. from waste materials - by low-temp. pyrolysis

Abstract: Prodn. of solid fuel from waste materials (esp. comminuted domestic refuse) is carried out by a process in which the fuel is obtd. in a form suitable for use in conventional combustion equipment (esp. in powder form), with the improvement that the waste material is first subjected to low-temp. pyrolysis. The process is superior to prior art processes w.r.t. environmental acceptability, thermal efficiency and equipment costs. More specifically, it is easier to remove Cl- and F-contg. pollutants from the small amt. of low-temp. pyrolysis gas than from large amts. of high-temp. pyrolysis or combustion gases.

High-power baseline and motoring test results for the GPU-3 Stirling engine

Abstract: Test results are given for the full power range of the engine with both helium and hydrogen working fluids. Comparisons are made to previous testing using an alternator and resistance load bank to absorb the engine output. Indicated power results are presented as determined by several methods. Motoring tests were run to aid in determining engine mechanical losses. Comparisons are made between the results of motoring and energy-balance methods for finding mechanical losses.

Process for recovering exhaust heat

Abstract: The present invention relates to a process for recovering the exhaust heat using the working fluid of the toluene (or benzene)-water system in the vapor cycle, when the moderate heat energy of 400°-750° C. is converted into work. In practice, in order to obtain the maximum overall thermal efficiency ηm, the working fluid of the Rankine cycle in the recovery of exhaust heat of the temperature of 400°-700° C. is suitable to be the mixture of toluene (or benzene) and water containing 20-80 mol. % of water, while the working fluid of the reheating cycle in the recovery of exhaust heat of the temperature of 600°-750° C. is suitable to be the mixture of toluene (or benzene) and water containing 45-90 mol. % of water in considerations of the thermodynamic efficiency of vapor cycle, the performance of the exhaust heat boiler and other factors.

Thermochemical water-splitting for hydrogen production. Final report 1 Jan 75-31 Dec 80. [Sulfur-iodine cycle]

Abstract: This report summarizes the work at GA on the sulfur-iodine water-splitting cycle It presents data for the SO2-I2-H2O reaction This reaction forms two separable phases: (1) one rich in H2SO4, (2) the other rich in HI This report describes how the H2SO4 phase is enhanced by further reaction on contact with I2(l) and SO2 Catalytic decomposition of vaporized H2SO4 into SO2, H2O, and O2 and recovery of these products was found to be feasible It reports on the conversion using H3PO4 of the HI product phase into the components, I2, H2O, and HI Both gaseous and liquid catalytic conversion of HI were found to be reasonable processes to produce H2 In addition, the task group at GA has tried to improve the cycle, particularly to better handle the HI-pregnant phase As a result of these studies, the sulfur-iodine water-splitting cycle is a leading candidate for commercialization with appropriate high-quality heat from fission reactors, fusion reactors, and concentrated solar energy Engineering evaluations have determined the thermal efficiency of the cycle to be about 47% Cost evaluations under way on another program of GA and done previously by other engineers support the commercial viability of the cycle

Surface treating material for heat exchanger

Abstract: PURPOSE:To enable to be proof against acid bedewed water by a structure wherein a main heat exchanger to reheat hot water is provided upstream an auxiliary heat exchanger in combustion gas passage and as well as the surface of the auxiliary heat exchanger is coated with Sn-Bi type corrosion resisting alloy. CONSTITUTION:In order to improve the thermal efficiency, the auxiliary heat exchanger for waste heat recovery is usually arranged downstream the main heat exchanger. However, because acid bedewed water is normally generated on the surface of the auxiliary heat exchanger, said surface is coated with corrosion resisting metal. The surface treating material for said coating consists of Sn-Bi type alloy containing 0.5-10wt% of Bi and coats the surface by immersion plating. The application of said surface treating material brings excellent corrosion resistance, keeping resultant heat conductivity nearly as equal to that of Sn and small contact angle of liquid drop, more smoothly falling down bedewed water and furthermore the melting point of the material is also equal to that of Sn. Accordingly, the heat exchanger A employed said surface treating material can stand for longer use as compared with conventional heat exchanger B.

Method and apparatus for heat storage in internal combustion engines

Abstract: Exhaust emissions are reduced, fuel consumption is improved for internal-combustion engines, and the number of cold starts reduced by storing heat energy from the operation of the engine in a heat-storage reservoir filled with a change-of-state heat-storage material. Absorbed heat energy is released back to the engine's intake manifold to maintain elevated engine temperature between uses and starting up of the engine.