Work entransy and its applications

The entransy theory has been applied to the analyses of heat-work conversion systems. The physical meaning and the applications of work entransy are analyzed and discussed in this paper. Work entransy, which is clarified to be a process dependent quantity, is not the entransy of work, but the system entransy change accompanying work transfer. The relationship between the work entransy and the output work is set up. When the application preconditions are satisfied, larger work entransy leads to larger output work. Entransy loss, which was proposed and applied to heat work conversion processes with irreversible heat transfer, is the net entransy flow into the system and the summation of work entransy and entransy dissipation. The application preconditions of entransy loss are also discussed.     

Entransy functions for steady heat transfer

In this paper, the entransy functions for steady heat transfer are summarized and discussed based on the variational theory and the entransy theory. The entransy functions for steady convective heat transfer are derived for the first time. In steady heat transfer processes, it is shown that the steady distributions of heat flux and temperature(radiative thermal potential) should make the corresponding entransy functions reach their minimum values when the temperature(radiative thermal potential) or the heat flux of the boundary is given. The extremum entransy dissipation principles and the minimum entransy-dissipation-based thermal resistance principles are compared with the entransy functions. It is shown that the entransy functions can describe a steady state,but cannot directly give a way to optimize heat transfer processes, while the extremum entransy dissipation principles and the minimum entransy-dissipation-based thermal resistance principles act in an opposite way.     

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

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 casting.The complex function was composed of the functions of the entransy dissipation and surface temperature gradient of the slab.The optimal water distribution at the sections of the secondary cooling zone were obtained.The 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 analyzed.The 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%,respectively.The quality and energy storage of the slab had obviously improved in this case.The 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 slab.Essentially,it is also the compromise between energy storage and quality of the slab.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.     

Application of entransy dissipation extremum principle in radiative heat transfer optimization

The concepts of entransy flux and entransy dissipation in radiative heat transfer were introduced based on the analogy with heat conduction and heat convection processes. Entransy will be partially dissipated during the radiative heat transfer processes due to the irreversibility. The extremum principle of entransy dissipation was developed for optimizing radiative heat transfer processes. This principle states that for a fixed boundary temperature the radiative heat transfer is optimized when the entransy dissipation is maximized, while for a fixed boundary heat flux the radiative heat transfer process is optimized when the entransy dissipation is minimized. Finally, examples for the application of the entransy dissipation extremum principle are presented. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2007CB206901)     

基于理论的相变储能换热器传热性能分析

在理论成功应用于常规换热器的基础上,将传递效率、耗散数及基于耗散的换热器热阻应用于相变储能换热器的传热性能分析中。定义广义耗散率并由此推导出相变储能换热器蓄热、放热及总过程的传递效率及其瞬时值。确定耗散数及基于耗散的换热器热阻计算中换热量的取法。选取一种相变储能装置作为分析对象,通过理论分析绘制各主要部分温度变化趋势,进一步简化得到硅油、水的出口温度表达式,作为算例分析基础。结果表明, 传递效率的应用范围最广,可用于计算相变储能换热器蓄热、放热及总过程的(瞬时)不可逆热损失,且评价结果与传热性能相符,瞬时传递效率随蓄热时间的增加先增大后不变再增大,随放热时间的增加先减小后不变再减小; 耗散数在蓄热过程和总过程中的评价结果与传递效率一致,瞬时耗散数随蓄热时间的增加先减小后不变再减小,然而在放热过程中的应用受限。基于耗散的换热器热阻的部分评价结果与实际不符,应用限制较大。蓄热过程及总过程中,当蓄热量、取热量与蓄、放热阶段时长同步变化时, 传递效率、耗散数与基于耗散的换热器热阻几乎无变化;当装置传热性能提高时, 传递效率增大, 耗散数减小,基于耗散的换热器热阻减小;放热过程中,设置参数的变化不影响装置传热性能, 传递效率基本无变化。     

对流换热可控温差场分布原则

应用火积概念导出了对流换热过程的火积耗散表达式,进一步基于火积耗散极值原理讨论了换热器N股冷、热流在不同情况下参与换热的优化。研究表明,若参与换热的任何冷、热流之间的温差可以独立调控,在总换热量一定寻求火积耗散最小或在总火积耗散一定的条件下寻求换热量最大,则整个换热系统冷、热流之间的温差分布均匀时换热最优;若参与换热的任何冷、热流体之间的换热量或火积损耗可独立确定,则换热冷热流之间的温差分别保持各自的均匀温差分布时换热最优;若在任何冷、热流之间存在可能换热的情况下,无论是总换热量一定时寻求火积耗散最小,还是总火积耗散一定时寻求换热量最大,整个换热系统不同的冷热流换热的优化温差并不是同一个常数。     

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

The entransy theory,which can be used to optimize the heat transfer network of a solar power tower system(SPTS)and improve 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(reducing 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?1 for a SPTS without re-heater when the total heat capacity 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.     

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

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 characteristics 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 ξ. 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.     

Constructal multidisciplinary optimization of electromagnet based on entransy dissipation minimization

Based on entransy dissipation, the mean temperature difference of solenoid (electromagnet) with high thermal conductivity material inserted is deduced, which can be taken as the fundament for heat transfer optimization using the extremum principle of entransy dissipation. Then, the electromagnet working at steady state (constant magnetic field, constant heat generating rate per unit volume) is optimized for entransy dissipation minimization (i.e. mean temperature difference minimization) with and without vo...     

热声热机换热器性能的分析

热声换热器热量传递的速率与效率直接影响着热声热机的性能. 　　耗散理论能更好地揭示换热器的传热优化特性,在热声换热器研究中引入　　耗散理论,针对顺流和逆流两种情况,计算了热声换热器的　　耗散热阻,并和最小熵产原理的结果进行了对比分析. 结果表明,在一定条件下,顺流比逆流情况下的不可逆损失要大;当换热器低温端流体的热容量小于高温端流体热容量时不可逆损失较小,结果最优.     

Heat transfer performance evaluation of one-stream heat exchangers and one-stream heat exchanger networks

One-stream heat exchangers and one-stream heat exchanger networks are widely used in engineering. In this paper, the heat transfer performance evaluation of one-stream heat exchangers and one-stream heat exchanger networks is analyzed with the concepts of entropy generation rate, entropy generation number, revised entropy generation number, entropy resistance, entransy dissipation rate, entransy dissipation number and generalized thermal resistance. For the analyzed one-stream heat exchangers, our numerical results show that the extremum value of the entransy dissipation rate and the minimum values of the entropy resistance and the generalized thermal resistance always lead to the largest heat transfer rate or the lowest temperature of the cooled object,while the minimum values of the other parameters do not always. For the analyzed one-stream heat exchanger networks, the minimizations of entransy dissipation rate, entransy dissipation number and generalized thermal resistance always correspond to the lowest average temperature of the cooled objects, while the minimizations of the other parameters do not. Therefore, only the extremum entransy dissipation principle and the minimum generalized thermal resistance principle are always applicable for the heat transfer performance evaluation of the systems in this paper, while the applicability of the other parameters is conditional.     

火积耗散理论在平行流热管换热器性能评价中的应用

火积耗散作为传热过程可逆性判断依据,可应用于换热器优化. 分析探究了热管换热器的温差、充液率、倾角及迎面风速对火积耗散的影响,利用焓差实验室进行平行流热管换热器性能试验. 随温差增大,火积耗散增大. 随充液率增大,火积耗散先增大后减小,温差越大,火积耗散变化幅度随充液率增大而增大. 增加倾角,火积耗散比未倾斜时小. 随迎面风速增大,火积耗散减小,且减小幅度随温差增大而增大. 相同传热量,火积耗散值最小时,为系统最优工况.     

Progress in optimization of mass transfer processes based on mass entransy dissipation extremum principle

The mass entransy and its dissipation extremum principle have opened up a new direction for the mass transfer optimization. Firstly, the emergence and development process of both the mass entransy and its dissipation extremum principle are reviewed. Secondly, the combination of the mass entransy dissipation extremum principle and the finite-time thermodynamics for optimizing the mass transfer processes of one-way isothermal mass transfer, two-way isothermal equimolar mass transfer, and isothermal throttling and isothermal crystallization are summarized. Thirdly, the combination of the mass entransy dissipation extremum principle and the constructal theory for optimizing the mass transfer processes of disc-to-point and volume-to-point problems are summarized. The scientific features of the mass entransy dissipation extremum principle are emphasized.     

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

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 exchangers.The entransy dissipation method is applied to the performance optimization of air-cooled heat exchangers in this paper.Two 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 method.The 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 obtained.Based 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.     

Entransy analyses of the thermodynamic cycle in a turbojet engine

The analysis and the design of turbojet engines are of great importance to the improvement of the system performance.Many researchers focus on these topics,and many important and interesting results have been obtained.In this paper,the thermodynamic cycle in a turbojet engine is analyzed with the entransy theory and the T-Q diagram.The ideal thermodynamic cycle in which there is no inner irreversibility is analyzed,as well as the influences from some inner irreversible factors,such as the heat transfer process,the change of the component of the working fluid and the viscosity of the working fluid.For the discussed cases,it is shown that larger entransy loss rate always results in larger output power,while smaller entropy generation rate does not always.The corresponding T-Q diagrams are also presented,with which the change tendencies of the entransy loss rate and the output power can be shown very intuitively.It is shown that the entransy theory is applicable for analyzing the inner irreversible thermodynamic cycles discussed in this paper.Compared with the concept of entropy generation,the concept of entransy loss and the corresponding T-Q diagram are more suitable for describing the change of the output power of the analyzed turbojet engine no matter if the inner irreversible factors are considered.     

Analyses of thermodynamic performance for the endoreversible Otto cycle with the concepts of entropy generation and entransy

In this paper,power the the and endoreversible the Otto cycle is analyzed with the entropy generation minimization objectives,and the the entransy theory.of The output power,the heat-work conversion efficiency are taken as the optimization rate,and relationships the output heat-work conversion efficiency,entransy the entropy generation and the entropy generation rate numbers,the work entransy are loss rate,The entransy loss of coefficient,the dissipation rate the entransy variation associated with discussed.applicability entropy the entropy generation minimization and the entransy theory while to the analyses is also analyzed.It is found do that smaller generation rate does not always lead to larger output our power,smaller entropy entransy generation loss numbers and not always lead to larger heat-work conversion efficiency,either.larger the In calculations,power,both larger larger rate larger entransy variation heat-work rate associated with work correspond also to that output while entransy is loss coefficient suitable results the in larger conversion developed efficiency.It is found concept of entransy dissipation not always for analyses because it was for heat transfer.     

An area method for visualizing heat-transfer imperfection of a heat exchanger network in terms of temperature–heat-flow-rate diagrams

The identification of the imperfection originating from finite-temperature-difference heat transfer is an indispensable step for both the performance analysis and the better design of a heat exchanger network(HEN) with the aim of energy saving. This study develops a convenient area method for visualizing the heat-transfer imperfection of a HEN in terms of temperature–heat flow diagrams( T-Q diagrams) by combining the composite curves that have already been used in pinch analysis and the recently developed entransy analysis. It is shown that the area between the hot and cold composite curves and the hot and cold utility lines on a T-Q diagram is just equal to the total entransy dissipation rate during the multi-stream heat transfer process occurred in a HEN, and this area can be used to graphically represent the total heat-transfer imperfection of the HEN. The increase in heat recovery or decrease in energy requirements with decreasing the minimum temperature difference, ΔT_(min), of a HEN can then be attributed to a lower entransy dissipation rate, quantitatively represented by the decrease of the area between the composite curves and the utility lines. In addition, the differences between the T-Q diagram and the pre-existing energy level–enthalpy flow diagram(Ω-H diagram) in the roles of visualizing process imperfection and designing HENs are discussed.     

物质波动性与粒子性的科学表征及光子与姗子的相互转化

重新审视了笔者提出的弥聚子论中的全宇观波粒二象性关系的正确性,重点探究了作为微观、介观、宏观实物体抽象化存在的弥聚子的波动性与粒子性的表征问题,并得出了新的结论,即波动性的自然强度应以单位频率所蕴含的能量或单位波数所蕴含的动量来表征,而粒子性的自然强度则应以单位能量所对应的频率或单位动量所对应的波数来表征,进而得出了全宇观量子化变量在趋于宏观极限时取极小值的新见解,并给出了"双极归一化"波动性强度和粒子性强度的定义,从而完善了全宇观波粒二象性关系. 继之,依据上述新见解,对笔者提出的全宇观不确定性原理进行了修正. 同时,深化了对于姗子(笔者预言的一种物质形态)特性的了解,指出了光子与姗子相互转化的必然性和基本规则,导出了全宇观量子化变量上下限之间的定量关系,重新诠释了自发发射、受激发射和受激吸收这3个典型的物理过程,预言了第4个物理过程的存在,并给出了包含这4个物理过程的、拓展了的爱因斯坦关系. 在此基础上,推测了姗子激射和实现"超级慢光"的可能性. 最后,指出了量子场的真空起伏可能是弥聚子几率波行为产生的根源. 上述工作使得弥聚子论进一步臻于完善,同时将光与物质相互作用的理论拓展为光子、姗子与物质相互作用的理论.     

Theoretical analyses of the performance of a concentrating photovoltaic/thermal solar system with a mathematical and physical model,entropy generation minimization and entransy theory

In this paper, the performance of a concentrating photovoltaic/thermal solar system is numerically analyzed with a mathematical and physical model. The variations of the electrical efficiency and the thermal efficiency with the operation parameters are calculated. It is found that the electrical efficiency increases at first and then decreases with increasing concentration ratio of the sunlight, while the thermal efficiency acts in an opposite manner. When the velocity of the cooling water increases, the electrical efficiency increases. Considering the solar system, the surface of the sun, the atmosphere and the environment, we can get a coupled energy system, which is analyzed with the entropy generation minimization and the entransy theory. This is the first time that the entransy theory is used to analyze photovoltaic/thermal solar system. When the concentration ratio is fixed, it is found that both the minimum entropy generation rate and the maximum entransy loss rate lead to the maximum electrical output power, while both the minimum entropy generation numbers and the maximum entransy loss coefficient lead to the maximum electrical efficiency. When the concentrated sunlight is not fixed, it is shown that neither smaller entropy generation rate nor larger entransy loss rate corresponds to larger electrical output power. Smaller entropy generation numbers do not result in larger electrical efficiency, either. However, larger entransy loss coefficient still corresponds to larger electrical efficiency.     

Equivalent thermal resistance minimization for a circular disc heat sink with reverting microchannels based on constructal theory and entransy theory

Thermal designs for microchannel heat sinks with laminar flow are conducted numerically by combining constructal theory and entransy theory. Three types of 3-D circular disc heat sink models, i.e. without collection microchannels, with center collection microchannels, and with edge collection microchannels, are established respectively. Compared with the entransy equivalent thermal resistances of circular disc heat sink without collection microchannels and circular disc heat sink with edge collection microchannels, that of circular disc heat sink with center collection microchannels is the minimum, so the overall heat transfer performance of circular disc heat sink with center collection microchannels has obvious advantages. Furthermore, the effects of microchannel branch number on maximum thermal resistance and entransy equivalent thermal resistance of circular disc heat sink with center collection microchannels are investigated under different mass flow rates and heat fluxes. With the mass flow rate increasing, both the maximum thermal resistances and the entransy equivalent thermal resistances of heat sinks with respective fixed microchannel branch number all gradually decrease. With the heat flux increasing, the maximum thermal resistances and the entransy equivalent thermal resistances of heat sinks with respective fixed microchannel branch number remain almost unchanged. With the same mass flow rate and heat flux, the larger the microchannel branch number, the smaller the maximum thermal resistance. While the optimal microchannel branch number corresponding to minimum entransy equivalent thermal resistance is 6.