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

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=T2dS, 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.