Finite-time Thermodynamic Method Research Articles

Exergy analysis of a lunar based solar thermal power system with finite-time thermodynamics

Abstract The exploration of the moon and the construction of the manned lunar outpost are the important parts of the deep space exploration. The continuous supply of thermal energy and power for deep space explorers and scientific equipment is a crucial issue to accomplish manned lunar missions. For most locations on the lunar surface, darkness lasts for periods of about 350 hours, so it is a great challenge for the solar photovoltaic cells and radioisotope thermoelectric generators to launch too much material from Earth. In the mission of manned deep space exploration, it is very necessary to utilize in situ resource effectively and sufficiently to reduce the hardware must be brought from Earth and to meet the requirement of energy and life support system. This paper describes an exergy analysis of a lunar based solar thermal power system using the method of finite-time thermodynamics. The calculations indicate that the system can provide the desired energy for the equipment. The aim of this article is to provide the basis for the design of a solar-powered Stirling engine using thermal energy from the processed lunar regolith.

Entropy generation minimization of steam methane reforming reactor with linear phenomenological heat transfer law

This paper investigates a class of tubular plug flow steam methane reforming reactor coupling among heat exchange, fluid flow and chemical reaction, in which the heat transfer between the heat reservoir outside the conversion tube and the reactants inside the tube is assumed to obey the linear phenomenological heat transfer law [ q ∝ Δ ( T − 1 ) ]. Under the condition that all of the hydrogen production rate, the inlet pressure, the total inlet molar flow rate, the inert gas (N2) molar flow rate are given, and the reservoir temperature is assumed to be controllable completely, both the minimum entropy generation rate of the process and the corresponding optimal reservoir temperature profile are obtained for minimizing the total entropy generation due to heat transfer, fluid flow and chemical reaction and by applying the theory and method of finite time thermodynamics with the help of nonlinear programming method. The obtained results are also compared with other two classes of reference reactors under the heat transfer strategies of constant and linear reservoir temperature operations and the optimization results for the minimum entropy generation of the case with Newtonian heat transfer law [ q ∝ Δ ( T ) ]. The results show that compared to the two classes of the reference reactors, optimizing the reservoir temperature profiles could reduce the entropy generation by more than 58%, which is mainly due to the decrease in the entropy generation caused by heat transfer; a shorter reactor may perform equally well, and the optimal path shows immediate regions of either a constant thermal force or a constant chemical force; heat transfer laws have significant effects on the optimal temperature configurations of both the heat reservoir and the reaction mixture for the minimum entropy generation of the chemical reactor.

Finite-time thermodynamic analysis for a chemically driven heat engine based on probability theory

This paper studies the problem of power optimization of chemically driven heat engine obeying Arrhenius law kinetics. Respectively, the first and second order reaction kinetics models taking the rate coefficients of the chemical reaction as finite-time constraints has been analyzed by the methods of finite-time thermodynamics with the synthetical consideration about the optimal configuration of the coupling process between chemical reaction and heat engines, and the effects of the finite-time thermodynamic characteristics of the coupling relation between chemical reaction and heat engine on the power optimization has been obtained. Combining the numerical results of this paper and the previous analysis, there is always a finite optimal flow rate in the reactor that yields maximum power when chemical reactions drive these three kinds of heat engine models, but a generalized Carnot heat engine driven by a chemical reaction can obtain the maximum power output in the practical case, the optimal flow rate in which the model of a generalized Carnot engine obtains the maximum power output can make the fuel efficiency of the system approaches the optimal value simultaneously. The finite-time thermodynamic method based on probability analysis can more accurately describe various performance parameters of thermodynamic system, this paper establishes the probability model of the first order reaction kinetics theory by using the probability analysis method, and obtains the power and fuel efficiency fluctuation bounds of the chemically driven heat engines. The results can not only include the mean value that is the only information obtained by classical method, but also take the fluctuations in microscale into account. The probabilistic method can provide more abundant information in the prediction of practical performance for the micro-size systems.

Power optimization of chemically driven heat engine based on first and second order reaction kinetic theory and probability theory

The finite-time thermodynamic method based on probability analysis can more accurately describe various performance parameters of thermodynamic systems. Based on the relation between optimal efficiency and power output of a generalized Carnot heat engine with a finite high-temperature heat reservoir (heat source) and an infinite low-temperature heat reservoir (heat sink) and with the only irreversibility of heat transfer, this paper studies the problem of power optimization of chemically driven heat engine based on first and second order reaction kinetic theory, puts forward a model of the coupling heat engine which can be run periodically and obtains the effects of the finite-time thermodynamic characteristics of the coupling relation between chemical reaction and heat engine on the power optimization. The results show that the first order reaction kinetics model can use fuel more effectively, and can provide heat engine with higher temperature heat source to increase the power output of the heat engine. Moreover, the power fluctuation bounds of the chemically driven heat engine are obtained by using the probability analysis method. The results may provide some guidelines for the character analysis and power optimization of the chemically driven heat engines.

Exploring the operation of a microscopic energy selective electron engine

The operation characteristics of a microscopic energy selective electron (ESE) engine system that operates respectively as heat engine, refrigerator or heat pump is extensively explored. The relationship between the transmission probability function and the electron engine operating regime is discussed in detail. The optimal performance for the electron engine system operating in different modes (heat engine, refrigerator, or heat pump) with different transmission probability functions and operating regimes are systematically studied with the optimization methods of finite time thermodynamics. Moreover, impacts of the electron engine design parameters such as phonon heat leakage, resonance width and central energy level on performance characteristics for the device with different transmission probability functions are investigated. The influences of transmission probability functions are analyzed by the performance comparisons between the ESE engine system considering a Lorentz transmission probability function and that considering a rectangular transmission probability function.

Analysis of Ecological of Characteristic Time for Thermoacoustic Refrigerator by Double Acoustic Drivers

Using the method of finite time thermodynamics, and quoting the ecology objective function to optimize the performance of the dual sound source driven thermoacoustic refrigerator regenerator. And Use the characteristic time to characterize the transducer effect in the thermoacoustic system in order to seek the optimal relationship between the characteristic time and ecology objective function. Numerical calculation results show that the impact of the relationship between ecological function and the characteristic time is parabolic curve, so there is an optimal characteristic time to maximize ecological objective function values.

A generalized model of an irreversible thermal Brownian refrigerator and its performance

A generalized model of an irreversible thermal Brownian refrigerator, which consists of Brownian particles moving in a periodic sawtooth potential with external forces and contacting with the alternating hot and cold reservoirs along the space coordinate, is established in this paper. The heat flows driven by both potential and kinetic energies of the particles as well as the heat leakage between the hot and cold reservoirs are taken into account. The optimum performance of the generalized model is analyzed using the theory and method of finite time thermodynamics. The analytical expressions for cooling load, coefficient of performance (COP) and power input of the Brownian refrigerator are derived. It is shown by numerical examples that due to the heat leakage between the heat reservoirs and heat flow via the change of kinetic energy of the particles, the Brownian refrigerator is always irreversible and the COP can never attain the Carnot COP. The influences of the heat leakage, the external force, barrier height of the potential, asymmetry of the sawtooth potential and temperature ratio of the heat reservoirs on the performance of the Brownian refrigerator are also investigated in detail. The effective regions of external force and barrier height of the potential in which the Brownian motor can operate as a refrigerator are determined. It is found that the performance of the Brownian refrigerator depends strictly on the design parameters. If these design parameters are properly chosen, the Brownian refrigerator can be controlled to operate in the optimal regimes. The results obtained herein about the general Brownian refrigerator model include those obtained in many previous literatures.

Optimization of cooling load and coefficient of performance for real regenerated air refrigerator

The performance analysis and optimization of a real regenerated air refrigerator is carried out by using finite-time thermodynamic method in this article. To maximize the cooling load and the coefficient of performance of the refrigerator, the heat conductance distribution between the hot- and cold-side exchangers and the regenerator for the fixed total heat exchanger inventory and heat capacitance rate matching between the working fluid and heat reservoirs are optimized, respectively. The influences of the pressure ratio, the total heat exchanger inventory, the efficiencies of the compressor and expander, the pressure recovery coefficient, and the ratio of the heat capacitance rates of heat reservoirs on the optimum characteristic of the refrigerator are shown by detailed numerical examples. The results obtained may provide guidance for the design of practice air refrigeration plants.

Comparative performance analysis for endoreversible simple air refrigeration cycles considering ecological, exergetic efficiency and cooling load objectives

SYNOPSIS On the basis of exergetic analysis, the performance analysis and optimisation of endoreversible simple air refrigeration cycles with constant-temperature heat reservoirs is carried out by using the finite-time thermodynamic method in this paper. The expressions for cooling load, ecological function and exergetic efficiency of the refrigeration cycle are derived. The influences of pressure ratio of the compressor and allocation of heat exchanger inventory on the optimal performance of the cycle are investigated by detailed numerical examples. Performance comparisons between ecological optimisation objective, exergetic efficiency optimisation objective and traditional cooling load optimisation objective are performed. The results may provide guidelines for the design and optimisation of practical refrigeration plants.

Irreversibility and Limiting Possibilities of Macrocontrolled Systems II: Microeconomics

The methods of finite time thermodynamics are used to solve the maximal profit problem in irreversible microeconomic systems, similar to the problems of generalized exergy, which were solved in the first part of the paper. The condition of equilibrium in open microeconomic systems is obtained.

Effect of Heat Transfer on the Performance of Thermoelectric Heat Pumps

AbstractThe performance analysis of thermoelectric (semiconductor) heat pumps is performedusing the combined method of finite time thermodynamics and non-equilibriumthermodynamics. The heating load and coefficient of performance (COP) expressionsfor the heat pump, which is composed of multi-elements, are derived with con-siderations of heat transfer irreversibility in the heat exchangers between the heatpump and the external heat reservoirs as well as the other internal irreversibilities.Numerical examples are provided. The effects of heat transfer, the number of elementsand the other design parameters on the performance of the heat pump are analyzed.IntroductionSeveral authors have applied the combined method of finite time thermodynamics orentropy generation minimization [1–6] and non-equilibrium thermodynamics [7–9] tothe analysis of thermoelectric (semiconductor) heat pump [10–13]. They analyzed theeffect of finite-rate heat transfer between the thermoelectric device and its externalreservoirs on the performance of the single-element thermoelectric heat pump. Inpractice, a thermoelectric heat pump is composed of many fundamental thermoelectricelements. It is a multi-element device. In the present paper we will investigate thecharacteristics of multi-element thermoelectric heat pumps related to the irreversi-bilities of finite-rate heat transfer, Joulean heat inside the thermoelectric device, andthe heat leak through the thermoelectric couple leg. The expressions for the heatingload and the coefficient of performance (COP) of the multi-element thermoelectricheat pump are derived. The effects of various design parameters on the performance ofthe heat pump are analyzed.

00/02590 Analytical method of finite time thermodynamics about the physical and chemical performances of fuel cell

00/02590 Analytical method of finite time thermodynamics about the physical and chemical performances of fuel cell

Performance analysis for a real closed regenerated Brayton cycle via methods of finite-time thermodynamics

SYNOPSIS Performance analysis of a real power cycle has been performed using finite-time thermodynamics. The analytical formulae about the relations between power output and pressure ratio, and between efficiency and pressure ratio of a real closed regenerated Brayton cycle coupled to variable-temperature heat reservoirs are derived. In the analysis, the irreversibilities involve the heat resistance losses in the hot- and cold-side heat exchangers and the regenerator, the irreversible (non-isentropic) expansion and compression losses in the turbine and compressor, and the pressure drop loss in the pipe and system. The optimal performance characteristics of the cycle may be obtained by optimising the distribution of heat conductance or heat-transfer surface areas among two heat exchangers and regenerator, and the matching between working fluid and heat reservoirs. For the specified heat reservoir conditions, the power output is dependent on the effectiveness of the regenerator, and there exists an optimal matching among the effectivenesses of the hot- and cold-side heat exchangers and the regenerator. The influences of the effectiveness of the regenerator, the effectiveness of the hot- and cold-side heat exchangers, the efficiencies of the turbine and compressor, the pressure recovery coefficient and the inlet temperature ratio of the heat reservoirs on the power output and efficiency of the cycle are analysed by detailed numerical examples.

Performance of chemical engines with a mass leak

The performance of an isothermal chemical engine with finite-rate mass transfer and a mass leak is analysed in this paper. The relations between the optimal power output and the efficiency, the maximum power output and the corresponding efficiency and the maximum efficiency and the corresponding power output are derived on the basis of linear (Onsager) mass-transfer law using the analogous method of finite-time thermodynamics for a heat engine. There exists a maximum efficiency bound with nonzero power output besides the maximum power output bound with nonzero efficiency for the engine. This characteristic is different from that for the chemical engine with the sole irreversibility of finite-rate mass transfer. The optimal region of parameter selection for the engine is provided and the effect of the mass-transfer law is analysed.

Cogeneration of power and heat by using endoreversible Carnot engine

The annual worth for production of heat and power of an endoreversible Carnot engine is analyzed by using the methods of finite time thermodynamics. It was found that, in order to obtain the maximum annual worth of production of heat and power, in the design of such systems, the heat exchangers on the hot and cold sides of the Carnot engine must have equal products of their size and heat transfer coefficient. Also, for the maximum annual worth, the ratio of the lower and higher temperatures of the Carnot engine should have its optimal value.

Performance characteristic of isothermal chemical engines

Chemical engines process mass flow to convert the differences in chemical potentials into work. An isothermal endoreversible chemical engine, in which the sole irreversibility is finite-rate mass transfer, is modeled in this paper. The power versus efficiency relationships of the chemical engine, using the analogous method of finite-time thermodynamics for a heat engine, are derived. The performance comparison between a heat engine and a chemical heat engine is presented.

Maximum power of a•combined-cycle isothermal chemical engine

A chemical engine processes mass flow to convert the differences in chemical potentials into work. An isothermal endoreversible chemical engine, in which the sole irreversibility is finite-rate mass transfer, is modeled in this paper. The expression of maximum power from the model using the analogous method of finite-time thermodynamics for a combined-cycle heat engine is derived. An important result shows that the efficiency at maximum power output is half of the maximum efficiency for chemical and heat engines.

96/06763 A method for the assessment of the mineral/organic matter association of trace elements in coal

Chemical engines process mass flow to convert the differences in chemical potentials into work. An isothermal endoreversible chemical engine, in which the sole irreversibility is finite-rate mass transfer, is modeled in this paper. The power versus efficiency relationships of the chemical engine, using the analogous method of finite-time thermodynamics for a heat engine, are derived. The performance comparison between a heat engine and a chemical heat engine is presented.

96/06752 An energy-dispersive miniprobe multielement analyzer (EMMA) for direct analysis of Pb and other trace elements in peats

A chemical engine processes mass flow to convert the differences in chemical potentials into work. An isothermal endoreversible chemical engine, in which the sole irreversibility is finite-rate mass transfer, is modeled in this paper. The expression of maximum power from the model using the analogous method of finite-time thermodynamics for a combined-cycle heat engine is derived. An important result shows that the efficiency at maximum power output is half of the maximum efficiency for chemical and heat engines.

96/06762 Measurements of vapor pressures of heteroatom-containing PAH and coal-tar model mixtures

Chemical engines process mass flow to convert the differences in chemical potentials into work. An isothermal endoreversible chemical engine, in which the sole irreversibility is finite-rate mass transfer, is modeled in this paper. The power versus efficiency relationships of the chemical engine, using the analogous method of finite-time thermodynamics for a heat engine, are derived. The performance comparison between a heat engine and a chemical heat engine is presented.