有限热源斯特林热机的优化性能研究

应用有限时间热力学方法,探索有限热源、热阻和回热损失的斯特林热机的优化性能,得到一些新的性能参数,所得结论可为斯特林热机的研制和优化设计提供些新理论指导。     

复杂热源下不可逆诺维科夫热机最大功率输出

考虑实际热机工作下的旁通热漏和内部耗散等不可逆因素,建立了包括连续均匀分布、三角形分布、二次分布和帕累托分布等四种不同的统计概率分布高温热源温度下的广义不可逆诺维科夫热机模型,导出了热机最大输出功率及相应的热效率和熵产率随高温热源温度、内部不可逆性等因素变化的关系式。结果表明：热漏和内部耗散分别对热机性能有着不同的影响,热漏使统计热源温度分布下最大功率输出对应的热效率减小,同时也增大了熵产率,但对热机的最大功率输出无影响;内部耗散不可逆性使热机的最大输出功率及相应热效率均明显减小,但使熵产率先增大后减小;熵产率随高温热源温度的标准差增大而减小。研究结果对太阳能发电厂性能提升具有一定理论指导意义。     

Optimization of power and efficiency for an irreversible Diesel heat engine

A cyclic model of an irreversible Diesel heat engine is presented, in which the heat loss between the working fluid and the ambient during combustion, the irreversibility inside the cyclic working fluid resulting from friction, eddies flow, and other irreversible effects are taken into account. By using the thermodynamic analysis and optimal control theory methods, the analytical expressions of power output and efficiency of the Diesel heat engine are derived. Variations of the main performance parameters with the pressure ratio of the cycle are analyzed and calculated. The optimum operating region of the heat engine is determined. Moreover, the optimum criterion of some important parameters, such as the power output, efficiency, pressure ratio, and temperatures of the working fluid at the related state points are illustrated and discussed. The conclusions obtained in the present paper may provide some theoretical guidance for the optimal parameter design of a class of internal-combustion engines.     

Performance analysis of an irreversible Miller heat engine and its optimum criteria

An irreversible cycle model of the Miller heat engine is established, in which the multi-irreversibilities coming from the adiabatic compression and expansion processes, finite time processes and heat leak loss through the cylinder wall are taken into account. The power output and efficiency of the cycle are optimized with respect to the pressure ratio of the working substance. The optimum criteria of some important parameters such as the power output, efficiency and pressure ratio are given. The influence of some relevant design parameters is discussed. Moreover, it is expounded that the Otto and the Atkinson heat engines may be taken as two special cases of the Miller heat engine and that the optimal performance of the two heat engines may be directly derived from that of the Miller heat engine.     

Investigation on the optimal performance and design parameters of an irreversible solar-driven Braysson heat engine

An irreversible solar-driven Braysson thermal engine has been investigated, in which finite rate heat transfer with the radiation–convection mode from the high-temperature reservoir to the heat engine and the convection mode from the heat engine to the heat sink, and irreversible adiabatic processes are taken into account. Based on the thermodynamic analysis method, the analytic expressions of the power output and efficiency of the Braysson heat engine are derived. By using numerical value calculation, the effects of the isobaric temperature ratio, internal irreversibility parameter, temperature ratio of the thermal reservoirs as well as the allocation parameters involving the heat-transfer coefficients, and areas on the performance characteristics of the Braysson heat engine are analysed and discussed in detail. The results obtained in this paper are more general than the related conclusions published in the literature and may provide some parameter design reference for solar-driven heat engines.     

Finite-time power limit for solar-radiant Ericsson engines in space applications

The power output and thermal efficiency of a finite-time optimized solar-radiant Ericsson heat engine is studied. The thermodynamic model adopted is a regenerative gas Ericsson cycle coupled to a heat source and heat sink by radiant heat transfer. Both the heat source and heat sink have infinite heat capacity rates. Mathematical expressions for optimum power and the efficiency at optimum power are obtained for the cycle based on higher and lower temperature bounds. The results of this theoretical work provide a base line criteria for use in the performance evaluation and design of such engines as well as for use in performance comparisons with existing extra-terrestrial solar power plants.     

Theory and performance analysis of a new heat engine for concentrating solar power

The objectives of this paper are to introduce a new heat engine and evaluate its performance. The new heat engine uses a gas, such as air, nitrogen, or argon, as the working fluid and extracts thermal energy from a heat source as the energy input. The new heat engine may find extensive applications in renewable energy industries, such as concentrating solar power (CSP). Additionally, the heat engine may be employed to recover energy from exhaust streams of internal combustion engines, gas turbine engines, and various industrial processes. It may also work as a thermal‐to‐mechanical conversion system in a nuclear power plant and function as an external combustion engine in which the heat source is the combustion gas from an external combustion chamber. The heat engine is to mimic the performance of an air‐standard Otto cycle. This is achieved by drastically increasing the time duration of heat acquisition from the heat source in conjunction with the timing of the heat acquisition and a large heat transfer surface area. Performance simulations show that the new heat engine can potentially attain a thermal efficiency above 50% and a power output above 100 kW under open‐cycle operation. Additionally, the heat engine could significantly reduce CSP costs and operate in open cycles, effectively removing the difficulties of dry cooling requirement for CSP applications. Copyright © 2014 John Wiley & Sons, Ltd.     

基于集总参数法的坦克发动机热性能模型

发展了一个基于集总参数法的坦克发动机热性能模型，考虑了发动机燃烧室的传热、发动机主要部件的传热、冷却系统和润滑系统的工作及坦克动力舱内的空气流动，建立了燃烧气体与发动机部件、各部件之间、部件与冷却液、部件与润滑油、部件与动力舱空气之间的热耦合计算公式．对一台坦克涡轮增压柴油机的热性能进行了实例计算，结果证实这个模型可以用于坦克发动机热性能的研究．     

An irreversible heat engine model including three typical thermodynamic cycles and their optimum performance analysis

An irreversible Dual heat engine model, which can include the Otto and Diesel cycles, is established and used to investigate the influence of the multi-irreversibilities mainly resulting from the adiabatic processes, finite time processes and heat leak loss through the cylinder wall on the performance of the cycle. The power output and efficiency of the cycle are derived and optimized with respect to the pressure ratio of the working substance. The maximum power output and efficiency are calculated. The influence of the various design parameters on the performance of the cycle is analyzed. The optimum criteria of some important parameters such as the power output, efficiency and pressure ratio are given. Several special interesting cases are discussed. The results obtained are general, so that the optimal performance of irreversible Otto and Diesel cycles are included in two special cases of the Dual cycle and may be directly derived from that of the Dual heat engine. Moreover, the performance characteristic curves of the three heat engines are presented by using numerical examples.     

Performance analysis and parametric optimum criteria of an irreversible Atkinson heat-engine

Multi-irreversibilities, mainly resulting from the adiabatic processes, finite-time processes and heat loss through the cylinder wall, are considered in the cycle model of an Atkinson heat engine. The power output and efficiency of the cycle are derived by introducing the pressure ratio and the compression and expansion efficiencies. The performance characteristic curves of the cycle are presented. The bounds of the power output and efficiency are determined. The optimum criteria of some important parameters, such as the power output, efficiency and pressure ratio are given. The influences of the various design parameters on the performance of the cycle are analyzed in detail. The results obtained may provide a theoretical basis for both the optimal design and operation of real Atkinson heat engines.     

Development of an analytical model useful for micro heat engine analysis

A general endo-reversible heat engine model is presented for a combustion driven system. It is composed of a Carnot heat engine and a combustor operating at a specified temperature. The model is inspired by past work on ideal engine/combustor systems and the need for an analysis technique incorporating heat losses suffered by all practical micro engines. This latter consideration results from the necessary structural connections existing between the hot and ambient temperature sections of the engine. In the model developed here, a counterflow heat exchanger provides this structural connection while recovering a portion of the sensible heat in the exhaust flow. A thermal shunt resistance to the surroundings is used to account for conductive heat loss. Finally, a high degree of idealization is employed to obtain a closed form analytical solution for the operating conditions of the engine/combustor system which, in this case, is assumed to be at the maximum power point of the device.     

Performance characteristics of an irreversible solar-driven Braysson heat engine at maximum efficiency

A novel model of the solar-driven thermodynamic cycle system which consists of a solar collector and a Braysson heat engine is established. The performance characteristics of the system are optimized on the basis of the linear heat-loss model of a solar collector and the irreversible cycle model of a Braysson heat engine. The maximum efficiency of the system and the optimally operating temperature of the solar collector are determined and other relevant performance characteristics of the system are discussed. The results obtained here may provide some theoretical guidance for the optimal design and operation of solar-driven Braysson and Carnot heat engines.     

Maximum power density for an endoreversible carnot heat engine

An analysis using maximum power-density criteria has been carried out for an endoreversible Carnot heat engine. The results have been compared with known results on maximum power analysis. The design parameters at maximum power density lead to smaller and more efficient endoreversible Carnot heat engines than those working at maximum power output.     

Nonlinear design-point performance adaptation approaches and their comparisons for gas turbine applications

Accurate performance simulation and understanding of gas turbine engines is very useful for gas turbine manufacturers and users alike and such a simulation normally starts from its design point. When some of the engine component parameters for an existing engine are not available, they must be estimated in order that the performance analysis can be started. Therefore, the simulated design point performance of an engine may be slightly different from its actual performance. In this paper, two nonlinear gas turbine design-point performance adaptation approaches have been presented to best estimate the unknown component parameters and match available design point engine performance, one using a nonlinear matrix inverse adaptation method and the other using a Genetic Algorithm-based adaptation approach. The advantages and disadvantages of the two adaptation methods have been compared with each other. In the approaches, the component parameters may be compressor pressure ratios and efficiencies, turbine entry temperature, turbine efficiencies, engine mass flow rate, cooling flows, and by-pass ratio, etc. The engine performance parameters may be thrust and SFC for aero engines, shaft power, and thermal efficiency for industrial engines, gas path pressures, temperatures, etc. To select the most appropriate to-be-adapted component parameters, a sensitivity bar chart is used to analyze the sensitivity of all potential component parameters against the engine performance parameters. The two adaptation approaches have been applied to a model gas turbine engine. The application shows that the sensitivity bar chart is very useful in the selection of the to-be-adapted component parameters, and both adaptation approaches are able to produce good quality engine models at design point. The comparison of the two adaptation methods shows that the nonlinear matrix inverse method is faster and more accurate, while the genetic algorithm-based adaptation method is more robust but slower. Theoretically, both adaptation methods can be extended to other gas turbine engine performance modelling applications.     

Theory and experimental validation of cross-flow micro-channel heat exchanger module with reference to high Mach aircraft gas turbine engines

This study explores the design, analysis, and performance assessment of a new class of heat exchangers intended for high Mach aircraft gas turbine engines. Because the compressor air that is used to cool turbine blades and other components in a high Mach engine is itself too hot, aircraft fuel is needed to precool the compressor air, cooling is achieved with a new heat exchanger. The heat exchanger consists of a large number of miniature, closely-spaced modules. Within each module, the fuel flows through a series of parallel micro-channels, while the air flows externally over rows of short, straight fins perpendicular to the direction of fuel flow. A theoretical model was developed to predict the thermal performance of the module for various operating conditions. To confirm the accuracy of the model, a single module was constructed and tested using water to simulate the aircraft fuel. The theoretical model was used to predict the air temperature drop, water temperature rise, and heat transfer rate for each fluid stream. Comparisons between theory and experiment show good overall agreement in exit temperatures and heat transfer rates. This study shows the theoretical model is a reliable tool for predicting the performance of heat exchanger modules under actual fuel and air turbine engine conditions and for the design of aircraft heat exchangers of different sizes and design envelopes.     

Nonlinear design-point performance adaptation approaches and their comparisons for gas turbine applications

Accurate performance simulation and understanding of gas turbine engines is very useful for gas turbine manufacturers and users alike and such a simulation normally starts from its design point. When some of the engine component parameters for an existing engine are not available, they must be estimated in order that the performance analysis can be started. Therefore, the simulated design point performance of an engine may be slightly different from its actual performance. In this paper, two nonlinear gas turbine design-point performance adaptation approaches have been presented to best estimate the unknown component parameters and match available design point engine performance, one using a nonlinear matrix inverse adaptation method and the other using a Genetic Algorithm-based adaptation approach. The advantages and disadvantages of the two adaptation methods have been compared with each other. In the approaches, the component parameters may be compressor pressure ratios and efficiencies, turbine entry temperature, turbine efficiencies, engine mass flow rate, cooling flows, and bypass ratio, etc. The engine performance parameters may be thrust and SFC for aero engines, shaft power, and thermal efficiency for industrial engines, gas path pressures, temperatures, etc. To select the most appropriate to-be-adapted component parameters, a sensitivity bar chart is used to analyze the sensitivity of all potential component parameters against the engine performance parameters. The two adaptation approaches have been applied to a model gas turbine engine. The application shows that the sensitivity bar chart is very useful in the selection of the to-be-adapted component parameters, and both adaptation approaches are able to produce good quality engine models at design point. The comparison of the two adaptation methods shows that the nonlinear matrix inverse method is faster and more accurate, while the genetic algorithm-based adaptation method is more robust but slower. Theoretically, both adaptation methods can be extended to other gas turbine engine performance modelling applications.     

Optimum operating conditions of irreversible solar driven heat engines

An optimal performance analysis of an internally and externally irreversible solar driven heat engine has been carried out. A Carnot-type heat engine model for radiative and convective boundary conditions was used to consider the effects of the finite-rate heat transfer and internal irreversibilities. The power and power density functions have been derived and maximization of these functions has been carried out for various design parameters. The optimum design parameters have been derived and the obtained results for maximum power (MP) and maximum power density (MPD) conditions have been compared. The effects of the technical parameters on the performance have been investigated.     

Performance analysis and parametric optimum criteria of a class of irreversible fuel cell/heat engine hybrid systems

Based on the current models of solid oxide fuel cells and two-heat-source heat engines consisting of two isothermal and two polytropic processes, a general model of a class of fuel cell/heat engine hybrid systems is established, in which multi-irreversibilities existing in real hybrid systems are taken into account. Expressions for the efficiency and power output of the hybrid systems are analytically derived from the model. The curves of the efficiency and power output of the hybrid systems varying with the current density and the efficiency versus power output curves are represented through numerical calculation. The general performance characteristics of the hybrid systems are revealed and the optimum criteria of the main performance parameters are determined. The effects of some key irreversibilities existing in the fuel cell, regenerator and two-heat-source heat engine on the performance of the hybrid systems are discussed in detail. The results obtained here are very general and may be directly used to derive the various interesting conclusions of the hybrid systems which are operated under different special cases.     

埃里克森热机的(火用)经济和生态学优化性能

研究存在热阻和回热损失的埃里克森热机的(火用)经济优化性能和生态学优化性能,得到一些新的性能参数,并揭示了(火用)经济优化性能与生态学优化性能间的联系,所得结果具有普遍意义,可为埃里克森热机的研制和优化设计提供些新理论指导.     

A novel Swiss-Roll recuperator for the microturbine engine

The design and analysis of a Swiss-Roll recuperator are investigated using a theoretical approach, numerical simulation and an experimental approach. The novel Swiss-Roll recuperator is a primary surface-type heat exchanger for micro gas turbine engines. The preliminary design of the Swiss-Roll recuperator, which is based on theoretical analysis, provides the required channel width, number of turns and number of transfer units (NTUs) for a given effectiveness. Friction causing a pressure loss is also predicted. For a given recuperator design, model simulation was performed to provide insights and improve model performance. Comparison of numerical results and theoretical predictions for efficiency of heat recovery shows a 10% error; however, pressure drop predictions were consistent. Test results show that the engine with a recuperator has a thermal efficiency of 27%. Fuel consumption rate is 600 ml/min. Conversely, a microturbine without a recuperator has a thermal efficiency of 12%, and fuel consumption rate is 800 ml/min. This experimental result indicates the engine with a recuperator use at least 1.5 times less fuel than an engine without a recuperator. This experimental result is consistent with predictions from analytical and numerical solutions. An engine with a recuperator saves energy, is economical and produces low amounts of emissions.