Entransy definition and its balance equation for heat transfer with vaporization processes

Abstract

Entransy balance equations and the corresponding optimization principles for heat conduction, heat convection and thermal radiation have been established. This paper develops the entransy balance equation for a low speed steady flow system with vaporization processes. The definition of enthalpy entransy for a substance from solid state to vapor state is proposed. The expressions of entransy and entransy dissipation are derived with differential volume element integration and the concept of enthalpy entransy. The heat transfer between a vaporization stream and a hot stream in a heat exchanger is also analyzed with the entransy approach. The theoretical results show that the minimum entransy-dissipation-based thermal resistance always leads to the maximum heat exchanger effectiveness. A numerical example compared with the entropy generation approach verifies the theoretical analyses. For a heat exchanger network undergoing vaporization processes, the minimum entransy-dissipation-based thermal resistance is proved to be applicable as the optimization criteria for the maximum heat exchange rate. The minimum entransy-dissipation-based thermal resistance principle is applied to two numerical cases for the thermal conductance distribution optimization to obtain the maximum heat exchange rate.