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entransy dissipation minimization for a class of one-way isothermal mass transfer processes

Science China(Technological Sciences) 2011年第2期54卷 352-361页

作者： XIA ShaoJun CHEN LinGen SUN FengRui Postgraduate School Naval University of Engineering Wuhan 430033 China

A class of one-way isothermal mass transfer processes with Fick’s diffusive mass transfer law[g ∝Δ(c)]is investigated in this *** on the definition of the mass entransy,the entransy dissipation function which reflects the irreversibility of mass transfer ability loss is *** optimal concentration allocations of the key components corresponding to the highand low-concentration sides for the minimum entransy dissipation of the mass transfer process are obtained by applying opti- mal control theory and compared with the strategies of the minimum entropy generation,constant mass transfer flux(constant concentration difference),and constant concentration ratio(constant chemical potential difference).The results are as follows. For the optimal mass transfer strategy of the minimum entransy dissipation,the product of the square of the key component concentration difference between the high-and the low-concentration sides and the inert component concentration at the low-concentration side is a constant,while for that of the minimum entropy generation,the ratio of the square of the key com-ponent concentration difference between the high-and the low-concentration sides to the key component concentration at the low-concentration side is a constant;when the mass transfer process is not involved in energy conversion process,the optimi-zation principle should be the minimum entransy dissipation;the mass transfer strategy of constant concentration difference is superior to that of constant concentration *** results obtained in this paper can provide some theoretical guidelines for optimal designs and operations of practical mass transfer processes.

关键词： diffusive mass transfer law isothermal mass transfer entransy dissipation optimal control finite time thermodynamics

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Distribution optimization of circulating water in air-cooled heat exchangers for a typical indirect dry cooling system on the basis of entransy dissipation

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Science China(Technological Sciences) 2015年第4期58卷 617-629页

作者： SUN Jian YUAN Kai YANG Li Jun CHEN Lin DU Xiao Ze YANG Yong Ping Key Laboratory of Condition Monitoring and Control for Power Plant Equipments of Ministry of Education School of Energy Power and Mechanical Engineering North China Electric Power University

The flow and heat transfer of air-cooled heat exchangers play important roles in the performance of indirect dry cooling systems in power plants,so it is of benefit to the design and operation of a typical indirect dry cooling system to optimize the thermo-flow characteristics of air-cooled heat *** entransy dissipation method is applied to the performance optimization of air-cooled heat exchangers in this *** irreversible heat transfer processes in air-cooled heat exchangers,the heat transfer between circulating water and cooling air and the mixing of circulating water,are taken into account and analyzed by means of the entransy dissipation *** total entransy dissipation rate,which connects the geometrical parameters of air-cooled heat exchanger sectors and the heat capacity rates of the fluids to the heat flow rate in every sector,is *** on the mathematical relation and the conditional extremum method,an optimization equation group is derived,by which the air-cooled heat exchanger with known air-side parameters is optimized,showing that the entransy dissipation based optimization approach can contribute to the distribution optimization of circulating water in air-cooled heat exchangers of a typical indirect dry cooling system.

关键词： indirect dry cooling system air-cooled heat exchanger entransy dissipation optimization

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An entransy dissipation-based optimization principle for solar power tower plants

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Science China(Technological Sciences) 2014年第4期57卷 773-783页

作者： ZHENG ZhangJing HE YaLing LI YinShi Key Laboratory of Thermo-Fluid Science and Engineering of MOE School of Energy and Power Engineering Xi'an Jiaotong University

The entransy theory, which can be used to optimize the heat transfer network of a solar power tower system （SPTS） and im- prove its energy efficiency, was introduced in this paper. Firstly, the irreversibility of the heat transfer processes in a SPTS was analyzed and the total entransy dissipation equation of a SPTS was derived. Then, two types of optimization problems （reduc- ing the total circulating flow rate or the total heat-exchanging area） of a SPTS were solved with conditional extremum model based on the formulas of total entransy dissipation. Finally, the entransy dissipation-based optimization principle was applied to a simple SPTS without re-heater and a complex SPTS with a re-heater. The results showed that under the chosen calculation conditions the minimum total thermal conductance was 19306.03 W K-~ for a SPTS without re-heater when the total heat ca- pacity rate of heat transfer fluid （HTF） was 3200 W K-1. The minimum total thermal conductance was about 7.9% lower than the value predicted based on the typical outlet temperature of a receiver. This meant that the total heat exchange area or initial investment could be effectively reduced under the prescribed total HTF circulating flow rate. We also studied the variation trends of the two optimized results including minimum total HTF heat capacity rate and minimum total thermal conductance. The minimum total HTF heat capacity rate decreased with the given total thermal conductance, the minimum total thermal conductance decreased first and then increased with the given total HTF heat capacity rate. We also found that for a SPTS with a re-heater, the mixing temperature and the mixing position of HTF had significant effects on the two types of optimization problems.

关键词： solar power tower system entransy dissipation heat transfer network optimization

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Optimization of fin geometry in heat convection with entransy theory

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Chinese Physics B 2013年第2期22卷 139-144页

作者：程雪涛张勤昭徐向华新刚 Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of AerospaceTsinghua University Institute of Nuclear and New Energy Technology Tsinghua University

The entransy theory developed in recent years is used to optimize the aspect ratio of a plate fin in heat *** on a two-dimensional model,the theoretical analysis shows that the minimum thermal resistance defined with the concept of entransy dissipation corresponds to the maximum heat transfer rate when the temperature of the heating surface is *** the other hand,when the heat flux of the heating surface is fixed,the minimum thermal resistance corresponds to the minimum average temperature of the heating *** entropy optimization is also given for the heat transfer *** is observed that the minimum entropy generation,the minimum entropy generation number,and the minimum revised entropy generation number do not always correspond to the best heat transfer *** addition,the influence factors on the optimized aspect ratio of the plate fin are also *** optimized ratio decreases with the enhancement of heat convection,while it increases with fin thermal conductivity increasing.

关键词： entransy dissipation thermal resistance heat convection optimization fin efficiency

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Role of viscous heating in entransy analyses of convective heat transfer

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Science China(Technological Sciences) 2020年第10期63卷 2154-2162页

作者： CHENG XueTao WANG XiangYu LIANG XinGang Department of Science and Technology of Anhui Province Hefei 230091China Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of AerospaceTsinghua UniversityBeijing 100084China

The entransy theory is widely used and found to be effective in thermal analyses and *** researchers considered the entransy variation due to viscous heating as part of entransy dissipation and analyzed convective heat transfer based on the differential relationship between entropy and ***,it has been pointed out that the derivation of the differential relationship between entropy and entransy is *** this paper,the convective heat transfer processes with viscous heating is reconsidered and analyzed from the viewpoint of the energy conservation and the entransy balance *** is shown that the influence of the viscous heating is equivalent to that of an inner heat ***,the contribution of viscous heating to system entransy should not be treated as part of entransy dissipation,but entransy flow into the ***-stream parallel and counter flow heat exchangers with viscous heating and a thermal insulation transportation problem of heavy oil are taken as examples to verify the theoretical analyses *** the examples,the numerical results show that the entransy dissipation rates could be negative when the influence of the viscous heating on the system entransy is treated as part of the entransy *** is obviously ***,when the entransy contribution from the viscous heating to the system entransy is treated as entransy flow into the system,it is shown that the entransy dissipation rate is always positive,and the heat transfer processes can be well explained with the entransy theory.

关键词： entransy dissipation viscous heating convective heat transfer thermal analyses

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Analyses of an air conditioning system with entropy generation minimization and entransy theory

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Chinese Physics B 2016年第6期25卷 130-136页

作者：吴艳秋蔡黎吴鸿娟 Chongqing Three Gorges University Chongqing 404100 China

In this paper,based on the generalized heat transfer law,an air conditioning system is analyzed with the entropy generation minimization and the entransy *** the coefficient of performance（denoted as COP） and heat flow rate Qout which is released into the room as the optimization objectives,we discuss the applicabilities of the entropy generation minimization and entransy theory to the *** numerical cases are *** the numerical results and theoretical analyses,we can conclude that the optimization applicabilities of the two theories are *** Qout is the optimization objective,larger entransy increase rate always leads to larger Qout,while smaller entropy generation rate does *** we take COP as the optimization objective,neither the entropy generation minimization nor the concept of entransy increase is always ***,we find that the concept of entransy dissipation is not applicable for the discussed cases.

关键词： entropy generation entransy increase entransy dissipation optimization analyses finite time thermodynamics air conditioning system

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Progress of entransy analysis on the air-conditioning system in buildings

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Science China(Technological Sciences) 2016年第10期59卷 1463-1474页

作者： ZHANG Tao LIU XiaoHua TANG HaiDa LIU Jun Department of Building Science Tsinghua University School of Aerospace Tsinghua University

It is of great importance to improve the energy performance of the air-conditioning system for building energy conversation. entransy provides a novel perspective to investigate the losses existing in the air-conditioning system. The progress of entransy analysis in the air-conditioning system is comprehensively investigated in the present study. Firstly missions and characteris- tics of the air-conditioning system are analyzed with emphasis on heat or mass transfer process. It is found that reducing the temperature difference, i.e. reducing the entransy dissipation helps to improve the performance. entransy dissipations and thermal resistances of typical transfer processes in the air-conditioning system are presented. Characteristics of sensible heat transfer process and coupled heat and mass transfer processes are researched in terms of entransy dissipation analysis. Reasons leading to entransy dissipation are also clarified with the help of unmatched coefficient 4. Principles for reducing the entransy dissipation and constructing a high temperature cooling system are summarized on the basis of case studies in typical handling processes. It＇s recommended that reducing mixing process, improving match properties are main approaches to reduce the entransy dissipation. The present analysis is beneficial to casting light on the essence of the air-conditioning system and proposing novel approaches for performance optimization.

关键词： air-conditioning system temperature difference entransy dissipation thermal resistance performance optimization

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Generalized constructal optimization for the secondary cooling process of slab continuous casting based on entransy theory

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Science China(Technological Sciences) 2014年第4期57卷 784-795页

作者： FENG HuiJun CHEN LinGen XIE ZhiHui DING ZeMin SUN FengRui Institute of Thermal Science and Power Engineering Naval University of Engineering Military Key Laboratory for Naval Ship Power Engineering Naval University of Engineering College of Power Engineering Naval University of Engineering

Based on constructal theory and entransy theory,a generalized constructal optimization of a solidification heat transfer process of slab continuous casting for a specified total water flow rate in the secondary cooling zone was carried out.A complex function was taken as the optimization objective to perform the *** complex function was composed of the functions of the entransy dissipation and surface temperature gradient of the *** optimal water distribution at the sections of the secondary cooling zone were *** effects of the total water flow rate in the secondary cooling zone,casting speed,superheat and water distribution on the generalized constructal optimizations of the secondary cooling process were *** results show that on comparing the optimization results obtained based on the optimal water distributions of the 8 sections in the secondary cooling zone with those based on the initial ones,the complex function and the functions of the entransy dissipation and surface temperature gradient after optimization decreased by 43.25%,5.90%and 80.60%,*** quality and energy storage of the slab had obviously improved in this *** complex function,composed of the functions of the entransy dissipation and surface temperature gradient of the slab,was a compromise between the internal and surface temperature gradients of the ***,it is also the compromise between energy storage and quality of the ***"generalized constructal optimization"based on the minimum complex function can provide an optimal alternative scheme from the point of view of improving energy storage and quality for the parameter design and dynamic operation of the solidification heat transfer process of slab continuous casting.

关键词： slab continuous casting solidification heat transfer entransy dissipation complex function generalized constructal op- timization generalized thermodynamic optimization

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Assessment of two different optimization principles applied in heat conduction

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Science Bulletin 2015年第23期60卷 2041-2053页

作者： Wenzhe Qi Kai Guo Hui Liu Botan Liu Chunjiang Liu School of Chemical Engineering and Technology State Key Laboratory of Chemical Engineering Tianjin University Collaborative Innovation Center of Chemical Science and Engineering Tianjin University

Optimization principles play a crucial role in the intensification of the heat-transfer process. In this study, we assess and compare two principles, i.e., the entransy dissipation extremum(EDE) principle and the minimum entropy generation(MEG) principle, used in a typical ‘‘area to point’’ heat conduction problem solved via a cellular automaton algorithm. The simulated results indicate that both rules can ameliorate the tree-network conductive path, leading to a more uniform thermal field and lower average and maximum temperatures. In contrast to the MEG principle, the EDE principle is more appropriate to be linked to the algorithm when dealing with the‘‘area to point’’ heat conduction optimization, especially with a higher conductivity ratio, kp/k0, between the high conductivity material and the low conductivity material and the fraction of high conductivity, /0. With the analysis of total entransy dissipation rate and entropy generation of the domain optimized by two principles, the results indicate that the EDE principle is more suitable for the heattransfer processes without heat–work conversion. Moreover, optimization via reducing the total entransy dissipation rate exhibits better performance in decreasing the equivalent resistance theoretically.

关键词： Heat conduction entransy dissipation Entropy generation Optimization principle Cellular automaton

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The influence of viscous heating on the entransy in two-fluid heat exchangers

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Science China(Technological Sciences) 2011年第5期54卷 1267-1274页

作者： GUO JiangFeng XU MingTian CHENG Lin Institute of Thermal Science and Technology Shandong University Jinan 250061 China Insititute of Engineering Thermophysics Chinese Academy of Science Beijing 100190 China

In the present work, water and olive oil are taken as working fluids to study the influence of viscous heating on the entransy dissipation caused by heat transfer in two-fluid heat exchangers. The results show that the influence of viscous heating on the entransy loss associated with heat transfer can not be neglected for the liquids having large dynamic viscosity. The viscous heating effect maintains the heat transfer ability of the working fluids, relatively reduces the entransy loss in heat exchangers; the viscous heating effect relatively augments the entropy generation due to heat transfer and the available energy destruction in heat exchangers. For the working fluid having large dynamic viscosity, the increasing rates of the entransy and entropy generation contributed by the viscous heating are even larger than those contributed by heat transfer, when the mass flow rate of working fluid reaches a certain value under the fixed heat transfer area condition. Thus, the entransy loss rate decreases and the growth rate of entropy generation increases as the mass flow rate of the working fluid increases. Under the same other conditions, the heat transfer entransy loss rate and entropy generation rate per unit heat transfer rate obtained when the fluid having a smaller heat capacity rate is cold fluid are less than those obtained when the fluid having a smaller heat capacity rate is hot fluid.

关键词： entransy entransy dissipation viscous heating heat exchanger entropy generation

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