[火积]理论在热功转换过程中的应用探讨

Discussion on the application of entransy theory to heat-work conversion processes

分析和讨论了(火积)理论在热功转换过程的应用及其局限性.对Carnot循环的分析表明,Carnot循环中系统的(火积)是平衡的,但(火积)和熵之间不存在dG=T2dS这样的联系.对于一般热力学过程,分析表明,在热量传递到内可逆循环中间接对外做功时,现有的(火积)理论可用于系统的分析.讨论了热功转换过程分析中(火积)理论与熵理论的不同.分析表明,两个理论的分析角度及优化输出功的前提条件是不同的.熵产从可用能损失的角度分析热功转换过程,而(火积)理论则从热量势能消耗的角度.当输入系统的可用能给定或者输入系统的热量及热量进、出系统的热力学力给定时,熵产最小化对应于输出功最大;对于(火积)理论,则当输入系统的热量及热量进、出系统的温度给定时,最大(火积)损失对应于最大输出功.同时,它们各自均有局限性.当相应的前提条件不满足时,最大(火积)损失或最小熵产可能不与最大输出功相对应.

Applications and limitations of the entransy theory for heat-work conversion processes are analyzed and discussed in this paper. Our analyses for the Carnot cycle show that the system entransy of the Carnot cycle is in balance, but the relationship, dG = T2 dS, does not exsit between the concepts of entransy and entropy. Therefore, the concept of entropy cannot be replaced by the concept of entransy. For common thermodynamic processes, the analyses show that the present entransy theory is applicable when heat is transferred into an endoreversible thermodynamic cycle to do work. In addition, in the analyses of heat-work conversion processes, the differences between the entransy theory and entropy theory are also discussed. It is shown that the viewpoints and preconditions of the two theories for the analyses and optimizations of heat-work conversion processes are different. The viewpoint of the analyses of entropy generation is the loss of exergy, while that of the analyses of entransy is the consumption of thermal potential. When the input exergy flow of the discussed system is prescribed or the input heat flow and the corresponding thermodynamic forces of the heat flows into and out of the system are prescribed, the entropy generation minimization leads to the maximum output work. For the entransy theory, the maximum entransy loss corresponds to the maximum output work when the input heat flow and the corresponding temperatures of the heat flows into and out of the system are prescribed. Meanwhile,they both have limitations. When the corresponding preconditions are not satisfied, the maximum entransy loss or the minimum entropy generation may not correspond to the maximum output work.