Useful entransy—A physical quantity describing the useful heat transfer ability for heating/cooling

Abstract

The existing entransy theory does not consider the usefulness of heat transfer ability. This leads to the fact that the heat transfer ability described by entransy is not completely consistent with the heat/cold utilization, and the entransy efficiency analysis also has certain limitations. Hence, this paper first studies the usefulness of heat transfer ability. Under the ambient air with infinite heat capacity, only the exothermic ability of the object above ambient temperature T0 is useful for heating, and only the endothermic ability of the object below T0 is useful for cooling. On this basis, with T0 as the reference point, the useful entransy is proposed to describe the useful heat transfer ability of an object for heating/cooling. It is demonstrated that heating/cooling mainly utilizes the heat transfer ability of an object relative to T0 (useful entransy), rather than its heat transfer ability relative to 0 K (entransy). Moreover, taking latent heat storage as an example, it is proved that the useful entransy efficiency is more accurate than the entransy efficiency to evaluate the heat transfer irreversibility. And the guidance based on useful entransy efficiency is more practical. Furthermore, useful entransy efficiency analysis and entransy dissipation analysis are complementary. The combination of the two can evaluate and analyze the heat transfer performance more comprehensively. In summary, the useful entransy is an important improvement of entransy theory.