Showing papers on "Thermodynamic cycle published in 1993"
TL;DR: In this paper, the performance of a double-effect cycle for continuous refrigeration is analyzed, allowing the infinite sink temperature and the couples of reactive salts to be used, which depend on the production temperature envisaged, to be selected.
Abstract: With the four components of a chemical heat pump (two solid-gas reactors, an evaporator and a condenser), a cycle of the double-effect type can be applied to continuous refrigeration. The performance of this process is analysed, allowing the infinite sink temperature and the couples of reactive salts to be used, which depend on the production temperature envisaged, to be selected. The results are presented in a diagram from which may be determined the required source temperature (as a function of the refrigeration temperature), the machine's coefficient of performance, its exergetic efficiency and the equilibrium drop, i.e. the power level that can be reached. This process is compared to the double-effect cycle developed on solid adsorption machines. The useful domain of these machines lies between + 10°C and − 70°C for COPs varying from 0.4 to 0.8.
181 citations
Patent•
03 Nov 1993
TL;DR: In this paper, a method and apparatus for implementing a thermodynamic cycle that includes expanding a gaseous working stream, transforming its energy into usable form and producing a spent working stream is described.
Abstract: A method and apparatus for implementing a thermodynamic cycle that includes: (a) expanding a gaseous working stream, transforming its energy into usable form and producing a spent working stream; (b) heating a multicomponent oncoming liquid working stream by partially condensing the spent working stream; and (c) evaporating the heated working stream to form the gaseous working stream using heat produced by a combination of cooling geothermal liquid and condensing geothermal steam.
96 citations
TL;DR: In this paper, a simulation model of the actual processes occurring during the thermodynamic cycle of a real spark ignition engine is developed, incorporating such important features as heat exchange of the cylinder gases with the chamber walls (during all phases), real spark timing, real valve opening and closing timings, accurate simulation of the spherical flame front movement issuing from the spark plug and calculation of eight chemical species concentration during combustion, at every engine degree crank angle.
91 citations
Patent•
26 Jul 1993
TL;DR: An expandable chamber piston type internal combustion engine operating in an open thermodynamic cycle includes a combustion process having a constant volume (isochoric) phase followed by a constant temperature (isothermal) phase.
Abstract: An expandable chamber piston type internal combustion engine operating in an open thermodynamic cycle includes a combustion process having a constant volume (isochoric) phase followed by a constant temperature (isothermal) phase.
66 citations
TL;DR: In this paper, an analysis of the thermodynamic cycles commonly used for the liquefaction of hydrogen in order to predict their performance under a given set of operating conditions and component efficiencies is presented.
59 citations
Patent•
10 Jun 1993
TL;DR: The Modified Ericsson cycle as discussed by the authors is an extension of the regenerative Brayton cycle that can include 2,3,4, or more stages (number of intercooling and heat/reheat cycles between stages) that achieve higher efficiencies and power density (net output power/cycle weight flow rate) than those of regenerative and non-regenerative cycles.
Abstract: This disclosure is the use of high efficiency turbomachinery designs to achieve high efficiency thermodynamic cycles. The high efficiency thermodynamic cycles are referred to as the Modified Ericsson cycles, an expansion of the regenerative Brayton cycle. A Modified Ericsson cycle can include 2,3,4, or more stages (number of intercooling and heat/reheat cycles between stages) that achieve higher efficiencies and power density (net output power/cycle weight flow rate) than those of regenerative and nonregenerative Brayton cycles. Also included is a high temperature tip-turbine driven compressor design for Brayton, Modified Ericsson and other power/refrigeration cycles.
53 citations
Patent•
19 Oct 1993
TL;DR: A Modified Ericsson Turbocharged Reciprocating Engine (METRE) was proposed in this article, which exhibits a high thermal efficiency for power and refrigeration applications by combining a turbocompressor and a multi-piston reciprocating engine.
Abstract: A Modified Ericsson Turbocharged Reciprocating Engine (METRE), is provided which exhibits a high thermal efficiency for power and refrigeration applications A Modified Ericsson cycle can include 2, 3, 4, or more stages (number of intercooling and heat/reheat cycles between stages) As stages are added, both cycle efficiency and power density (power/weight flow) increase, therefore, trade-offs between higher performance and number of stages (system complexity, cost, etc) are necessary to optimize the engine By combining a turbocompressor for the low pressures of the cycle and a multi-piston reciprocating engine for the high pressures of the cycle, a light weight, highly fuel-efficient, low-polluting, engine can be achieved The METRE is highly suited for the power range of automobiles and trucks This engine can use low technology (lower turbine temperatures, efficiencies, etc) as well as high technology components (higher turbine temperatures, efficiency etc) and remain competitive with Brayton, Stirling, gas and Diesel engines The Ericsson cycle, like the Brayton and Stirling, utilizes external combustion or heating and thus can use readily available optional fuels such as natural gas, kerosene, propane, butane and gases derived from coal Solar and nuclear energy are also useable heat source candidates
37 citations
TL;DR: In this article, a vapour compression simulation model was developed to predict the operating point of the system (including condensing and evaporating pressures) as a function of equipment characteristics (for example, compressor swept volume, speed and clearance ratio, and heat exchanger overall conductances).
Abstract: A vapour compression simulation model was developed. Simple mathematical models were employed for each component of the cycle. They resulted in a set of nonlinear equations, which was solved numerically. Heat losses from condenser to ambient were included. The model is capable of predicting the operating point of the system (including condensing and evaporating pressures) as a function of equipment characteristics (for example, compressor swept volume, speed and clearance ratio, and heat exchanger overall conductances) and prevailing thermodynamic conditions (such as heat source and heat sink temperatures with the mass flow rates of their fluids). The predicted performance was compared to that of an existing R-12 unit, showing good agreement. As an application, a comparative analysis is made on the thermodynamic performance of a domestic heat pump running on two different refrigerants: R-12 and R-134a.
32 citations
TL;DR: In this article, a new Carnot model operating with two heat engines and two mechanical heat pumps is defined to be the correct and logical way to describe the mechanical analogy for an absorption heat pump and a heat transformer.
Abstract: Comparison of different absorption heat cycles is not always made on the correct manner. This also includes comparison of an ideal absorption cycle with a mechanical analogy. A new Carnot model operating with two heat engines and two mechanical heat pumps is defined to be the correct and logical way to describe the mechanical analogy for an absorption heat pump and an absorption heat transformer. General equations for the Carnot coefficient of performance, COPr, are exemplified and simulated for an absorption heat pump and an absorption heat transformer, and an entropy flow fraction diagram is introduced. The important fact that the absorption heat cycles must operate under the same conditions when they are compared is discussed.
28 citations
Patent•
20 Aug 1993TL;DR: In this paper, an absorption heat pump having an an evaporator, an absorber, a high-temperature regenerator, a low-time temperature regenerator and a condenser is combined with a fuel cell such that the pump includes a cycle in which vapor exhaust heat from the fuel cell is used as a heat source for the evaporator and the high temperature regenerators.
Abstract: An absorption heat pump and a cogeneration system are provided to have high efficiency of utilizing exhaust heat. An absorption heat pump having an evaporator, an absorber, a high-temperature regenerator, a low-temperature regenerator and a condenser is combined with a fuel cell such that the pump includes a cycle in which vapor exhaust heat from the fuel cell is used as a heat source for the evaporator and the high-temperature regenerator, and another cycle in which warm-water exhaust heat from the fuel cell is used as a heat source for the low-temperature regenerator.
26 citations
TL;DR: In this paper, the thermodynamic inequality derived in the preceding paper is examined in the context of Carnot-like cyclic processes, and a geometrical picture is developed which vividly describes a number of important results.
Abstract: Physical implications of the thermodynamic inequality derived in the preceding paper are examined in the context of Carnot‐like cyclic processes. In terms of the power P and the degradation D associated with such a process, a geometrical picture is developed which vividly describes a number of important results. Our picture also leads to the concept of time efficiency as a natural complement to the concept of power efficiency. Extensions to Carnot‐like refrigerators and heat pumps are carried out. Finally, the influence of a heat leak between the two reservoirs is analyzed.
Journal Article•
TL;DR: The need for industry to move away from mains-powered vapour-compression refrigerators towards environmentally safer heat-powered cycles, as part of a "total energy" system along with, for example, gas-powered CHP plants, was highlighted in this paper.
Abstract: This paper argues the need for industry to move away from mains-powered vapour-compression refrigerators towards environmentally safer heat-powered cycles, as part of a 'total energy' system along with, for example, gas-powered CHP plants. There is an increasing need for small-scale heat-powered refrigerators and heat pumps designed specifically for use in the light commercial sector. Such devices will provide an economic use of fossil fuels and reductions in CO[sub 2] emissions, along with a potential for using environmentally friendlier refrigerants, such as water. A number of heat-powered refrigerator cycle options are described, and a review of current research is provided. It is hoped that this contribution will stimulate wider interest in the technology of heat-powered refrigeration. 100 refs., 12 figs., 1 tab.
TL;DR: Binary-flashing units utilize new types of geothermal power cycles, which may be used with resources of relatively low temperatures (less than 150 C) where other cycles result in very low efficiencies.
Abstract: Binary-flashing units utilize new types of geothermal power cycles, which may be used with resources of relatively low temperatures (less than 150 C) where other cycles result in very low efficiencies. The thermodynamic cycles for the binary-flashing units are combinations of the geothermal binary and flashing cycles. They have most of the advantages of these two conventionally used cycles, but avoid the high irreversibilities associated with some of their processes. Any fluid with suitable thermodynamic properties may be used in the secondary Rankine cycle. At the optimum design conditions binary-flashing geothermal power plants may provide up to 25 percent more power than the conventional geothermal units.
TL;DR: In this article, a dual-loop absorption machine with a solution of lithium bromide-water is presented. But the working fluid pair is not used for transferring refrigerant between the loops, and the calculated COPs are of the order of 1.8.
Abstract: The search for high-efficiency, gas-fired cooling cycles has led to the development of dual-loop absorption machines with cooling coefficients of performance (COPs) in the 1.2 to 1.7 range. This increased performance may call for high generator temperatures, new working fluids or new materials of construction. In most cases, two different sets of working fluids are required. The conceptual design presented here is aimed at obtaining high efficiencies with relatively low temperatures, employing only one set of fluids. The concept consists of two loops coupled in a configuration aimed at minimizing the loss of thermodynamic availability incurred when transferring refrigerant between the loops. The working fluid pair is a solution of lithium bromide-water. The calculated COPs are of the order of 1.8. The cycle relies on an elaborate evaporator-absorber combination. The paper presents the conceptual design, the critical assumptions, and the performance calculations for the concept.
TL;DR: In this article, the thermodynamic cycle appropriate to an alkali metal thermal-to-electric converter cell is discussed for both liquid-and vapor-fed modes of operation, under the assumption that all processes can be performed reversibly.
Abstract: An AMTEC cell, may be described as performing two distinct energy conversion processes: (i) conversion of heat to mechanical energy via a sodium-based heat engine and (ii) conversion of mechanical energy to electrical energy by utilizing the special properties of the electrolyte material. The thermodynamic cycle appropriate to an alkali metal thermal-to-electric converter cell is discussed for both liquid- and vapor-fed modes of operation, under the assumption that all processes can be performed reversibly. In the liquid-fed mode, the reversible efficiency is greater than 89.6% of Carnot efficiency for heat input and rejection temperatures (900--1,300 and 400--800 K, respectively) typical of practical devices. Vapor-fed cells can approach the efficiency of liquid-fed cells. Quantitative estimates confirm that the efficiency is insensitive to either the work required to pressurize the sodium liquid or the details of the state changes associated with cooling the low pressure sodium gas to the heat rejection temperature.
TL;DR: In this article, the authors examined the mechanical efficiency of reciprocating heat engines in a general setting and derived an upper bound on the compression ratio under conditions relating the level of performance of the mechanism to the ratio of engine operating temperatures, which has implications for the design of engines intended for operation from low grade sources such as industrial waste heat or passive solar energy.
Abstract: This paper examines the mechanical efficiency of reciprocating heat engines in a general setting. From an abstract mathematical characterization of machines, the relation of the pressure-volume cycle of an engine and the characteristics of its mechanism to its useful work output is established. Using the ideal Stirling engine in conjunction with this relation, a functional upper bound on the mechanical efficiency of all engines is derived. This shows the existence of limits on compression ratio under conditions relating the level of performance of the mechanism to the ratio of engine operating temperatures. This has implications for the design of engines intended for operation from low grade sources, such as industrial waste heat or passive solar energy.
TL;DR: In this paper, the optimal performance of endoreversible cycles was studied based on another linear heat transfer law (the heat-flux q varies as Delta (1/T)) in irreversible thermodynamics instead of Newton's law.
Abstract: Optimal performance of endoreversible cycles is studied systematically based on another linear heat transfer law (the heat-flux q varies as Delta (1/T)) in irreversible thermodynamics instead of Newton's law. First, a fundamental optimum formula for endoreversible cycles is derived by using a three-heat-source cycle model. Then, the formula is used to deduce the performance bounds of various endoreversible cycles. Some new results are obtained. These results are compared with those obtained by using Newton's law. Consequently, the common characters and the main differences of an endoreversible cycle for the two linear heat transfer laws are expounded. Finally, the effect of finiteness of the high-temperature heat source on the optimal performance of an endoreversible cycle for the two linear heat transfer laws is discussed.
TL;DR: The Carnot cycle as mentioned in this paper is a reversible cycle carried out by an ideal (ideal, not real) heat engine working with an ideal thermodynamic fluid, and the general concept of the thermodynamic cycle is sometimes used for comparisons with economic and biological processes, supposing the latter resemble the former.
TL;DR: In this paper, a closed cycle, Brayton gas-turbine plant with a heat exchanger powered by the sun has been studied, and a simple expression is derived for calculating the efficiency of the cycle in terms of the compression pressure ratio, the pressure loss coefficient and the ratio of the lower to higher temperature in the cycle with efficiency of various components.
Patent•
28 Sep 1993TL;DR: In this article, the proportionality of the volumetric capacities of a compressor and an expander is adjusted to approximate the densities of the liquid heat exchange fluid at the chosen working pressures.
Abstract: A machine, such as a heat pump, and having an all liquid heat exchange fl, operates over a more nearly ideal thermodynamic cycle by adjustment of the proportionality of the volumetric capacities of a compressor and an expander to approximate the proportionality of the densities of the liquid heat exchange fluid at the chosen working pressures. Preferred forms of a unit including both the compressor and the expander on a common shaft employs difference in axial lengths of rotary pumps of the gear or vane type to achieve the adjustment of volumetric capacity. Adjustment of the heat pump system for differing heat sink conditions preferably employs variable compression ratio pumps.
TL;DR: In this article, the equilibrium and reaction rate performance of pseudo-binary La 1-xYxNi5-yMny alloys were investigated with regard to their use in a −20 °C refrigeration system with a 130-150 °C thermally driven heat source, such as solar heat.
TL;DR: In this article, the optimal solar collector outlet temperature for maximizing the work output for an Otto air-standard cycle with ideal regeneration was investigated, and the effect of radiative and convective heat losses from the solar collector, on the optimum outlet temperature was presented.
01 Nov 1993
TL;DR: In this article, a nuclear space power system based on the ultrahigh temperature vapor-core reactor (UTVR) with magnetohydrodynamic (MHD) energy conversion is presented.
Abstract: This article presents the conceptual design of a nuclear space power system based on the ultrahigh temperature vapor-core reactor (UTVR) with magnetohydrodynamic (MHD) energy conversion. This UF4-fueled gas-core cavity reactor operates at a maximum core temperature of 4000 K and 40 atm. Potassium fluoride working fluid cools the reactor cavity wall and mixes with the fissioning fuel in the core. Neutron transport calculations with specialized high temperature gas-core cross-sectional libraries indicate criticality at core radii of 60-80 cm, with BeO reflector thicknesses of —50 cm. The heated core exhaust mixture is directed through a regeneratively cooled nozzle into a disk MHD channel to generate electrical power. The MHD generator operates at fluid conditions below 2300 K and 1 atm. Fission fragment ionization enhances the electrical conductivity in the channel significantly, allowing an overall conversion efficiency of 20%. The mixture is condensed in heat exchangers, and pumped back to the core in a MHD-Rankine thermodynamic cycle. Heat rejection temperatures of 1500-2100 K lead to compact heat exchangers and an overall specific weight of ~1 kg/kWe for 200 MWe. Material experiments, performed with UF4 up to 2200 K (to date), show acceptable compatibility with tungsten-, molybdenum-, and carbon-based materials. This article discusses the supporting nuclear, fluid flow, heat transfer and MHD analysis, materials experiments, and fissioning plasma physics.
TL;DR: In this article, a novel experimental technique has been developed to study a three-pressure absorption refrigeration cycle using R600-DMF as the working pair, where the third pressure was obtained by employing a liquid-gas ejector between the absorber and the evaporator.
Abstract: A novel experimental technique has been developed to study a three-pressure absorption refrigeration cycle using R600-DMF as the working pair. The third (or the intermediate) pressure is obtained by employing a liquid-gas ejector between the absorber and the evaporator. Pilot plant studies showed that it is possible to obtain high COP (0.4) when compared with a conventional two-pressure cycle. Parametric studies on the COP and the recirculation ratio have been made. A mathematical model has been developed and the results obtained have been compared with those obtained experimentally. The important result is that higher COP values could be obtained at lower generator temperatures.
TL;DR: In this article, it was shown that it is possible to obtain supplementary power by means of a Rankine cycle engine with the LH 2 utilized as a heat sink and with the atmosphere or exhaust gas as the heat source if an appropriate working fluid is selected.
TL;DR: In this paper, the hypothesis that systems of thermoregulation, similar to open-type micro heat pipes, exist in nature (soils, living organisms, plants) and in a number of technological processes (drying, thermodynamic cycles on solid adsorbents) is considered.
Abstract: The hypothesis that systems of thermoregulation, similar to open-type micro heat pipes, exist in nature (soils, living organisms, plants) and in a number of technological processes (drying, thermodynamic cycles on solid adsorbents) is considered. The hydrodynamics and heat transfer in such thermoregulation systems differ from the hydrodynamics and heat transfer in classical heat pipes, since their geometrical dimensions are extremely small (dozens of microns), adhesion forces are powerful, the effect of the field of capillary and gravitational forces is significant, and strong interaction between counter-current flows of vapor and liquid takes place.
TL;DR: In this article, a theoretical study of an application of the Brayton process for heat recovery systems in paper machines is presented, involving the development of a calculation model for the expansion process of moist air in turbines.
Abstract: A theoretical study of an application of the Brayton process for heat recovery systems in paper machines is presented, involving the development of a calculation model for the expansion process of moist air in turbines. The heat recovery systems are presented by means of temperature-entropy diagrams and the Brayton process is compared with a heat pump system based on the reverse Rankine process. The dependence of energy consumption is examined as a function of turbine and compressor efficiencies. The energy efficiency is also studied.
TL;DR: In this article, the authors used isothermal simulation with decoupled losses to obtain reliable predictions at practical levels of rpm for kinematic Stirling engines, and the method seems to be an adequate tool to study a large number of configurations, which the engineer needs at the initial design stage.
Abstract: Dimensional analysis has been employed to review the isothermal or quasi-static simulation of kinematic Stirling engines and to study the influence of the engine and drive mechanism types, and other parameters, on the thermodynamic engine cycle. The use of isothermal simulation with decoupled losses to obtain reliable predictions at practical levels of rpm is experimentally justified. The method seems to be an adequate tool to study a large number of configurations, which the engineer needs at the initial design stage. At the same time it provides a intuitive knowledge of and similarity criteria for the thermodynamic engine performance.
01 Jan 1993
TL;DR: In this article, a parametric analysis is performed to compare different heat pump based thermal control systems for a Lunar Base, and it is quantitatively demonstrated that absorption based systems are not mass competitive with Rankine systems.
Abstract: A parametric analysis is performed to compare different heat pump based thermal control systems for a Lunar Base. Rankine cycle and absorption cycle heat pumps are compared and optimized for a 100 kW cooling load. Variables include the use or lack of an interface heat exchanger, and different operating fluids. Optimization of system mass to radiator rejection temperature is performed. The results indicate a relatively small sensitivity of Rankine cycle system mass to these variables, with optimized system masses of about 6000 kg for the 100 kW thermal load. It is quantitaively demonstrated that absorption based systems are not mass competitive with Rankine systems.