Multiscale particle transport problems are widely present in the fields of precision manufacturing, nanomaterials, energy and power, national defense and military. Such problems involve large-scale length and time scales, which pose great challenges to physical modeling and numerical simulations. To study multiscale particle transport problems, cross-scale numerical simulation based on the Boltzmann transport equation has become an effective method, but the nonlinear, multi-scale, and high-dimensional characteristics of the equation pose great challenges to the stability, compatibility, computational effciency/accuracy, and asymptotic preservation of numerical methods. In recent years, many multiscale kinetic methods suitable for arbitrary Knudsen numbers have been developed, and the discrete unified gas kinetic scheme is one of them. Different from the traditional direct numerical interpolation scheme, the discrete unified gas kinetic scheme reconstructs the distribution function at the cell interface through the characteristic solution of the kinetic equation in both time and position space, thereby coupling, accumulating, and calculating particle transport and collision effects on a numerical time step scale. Based on the idea of incorporating the evolution inschemeion of physical equations into the construction process of numerical methods, the cell size and time step of this method are no longer limited by the mean free path and relaxation time of particles, and can adaptively and effciently simulate multiscale particle transport problems from the ballistic to diffusive limit. A large number of numerical results show that the present scheme has good numerical stability and low numerical dissipation, not limited to Knudsen number and Mach number. Based on the framework of finite volume method, this method has been successfully applied to micro/nano scale fluid flow and heat transfer, hypersonic aircraft, solid material thermal conduction, radiation, plasma and turbulence. This paper mainly reviews and prospects the development of this method in the field of multi-scale heat conduction in solid materials, including the application in phonon transport, electron-phonon coupling, phonon hydrodynamic heat conduction and thermal management of electronic equipment.
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