Open Access

ARTICLE

PHYSICAL HEAT TRANSFER

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a Department of Engineering Mechanics, Tsinghua University, Beijing 100084, People’s Republic of China

* Corresponding Author: Email:

Frontiers in Heat and Mass Transfer 2019, 13, 1-12. https://doi.org/10.5098/hmt.13.20

Abstract

The classical heat transfer theory is established on the empirical models of Fourier’s heat conduction law and Newton’s cooling law. Although the classical theory has been successfully used in a wide range of industrial engineering applications, it lacks deep understanding of the physical mechanisms for energy transport and analytical methodology based on solid mathematical and mechanical principles. The rapid development of modern science and technology challenges the traditional heat transfer theory in two aspects: (1) Fourier’s law of heat conduction is no longer valid under the ultra-fast laser heating or nanoscale conditions; (2) The optimization principle minimizing entropy generation is not suitable for heat transfer problems without heat to work conversion. In order to solve the first challenge, we re-examined the nature of heat and introduced new physical quantities, such as thermomass, thermomass velocity, thermomass energy. Then the heat transfer problems can be analyzed in the framework of vectorial fluid mechanics, and the thermomass momentum conservation equation has been established and known as a general law of heat transfer. For the second challenge, we introduced new physical quantities, entransy and entransy dissipation, by analogy between the heat conduction process and the electric conduction process. Unlike entropy as the core physical quantity in thermodynamics dealing with energy conversion, entransy is the quantity to represent the ability of heat transfer in an incompressible system. The entransy dissipation represents the irreversibility of heat transfer process. On this basis, the least action principle to minimize entransy dissipation can be used to optimize the heat transfer process and enhance energy efficiency. Because the physical essence of entransy is the thermomass potential energy, the entransy-based variational method is actually the energy method in heat transfer. All the new physical quantities, principles and methods form a new and independent knowledge system in heat transfer, which may be named “Physical heat transfer”.

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