Lattice Boltzmann Method For Microscale Fluid Flow, Heat And Mass Transfer

The fluid flow, heat and mass transfer in the Micro-electro-mechanical systems (MEMS), Fuel Cell and Micro-combustion have been obtained much more attentions in the world. Owing to the micro/nanometer scales appearing in such systems, the researches on the transports of gases should be considered such small scales effects. Recently, own to its kinetic background, the lattice Boltzmann method (LBM) has been applied to micro-scopic gas flows, however, the study of microscopic gas heat and mass transfer is quite rare. It is also observed that the LBM still has many fundamental problems at the macroscopic or microscopic gas flows. In addition, the application of LBE to the microscopic gas flows still has two critical problems, that is, the relation between relaxation time and Knudsen number, another is the boundary treatment of LBE. In sight of the above mentioned problems, this thesis will study such problems as following aspects:Firstly, we improve the theory of LBE in the field of heat and mass transfer, and then have a try to apply LBE models to investi-gating the microscopic heat and mass transfer problems. The contents of this thesis can be classified to two main aspects:(1) Theory of the LBE:First, a coupled multiple relaxation times (MRT) thermal LBE model is proposed, which overcome the fixed Prandt number and the inconsistent of the viscous coefficient in the existing multispeed LBE models; Second, two kinds of the ax-isymmetric thermal LBE models are introduced, which overcome the complex external force terms in the existing axisymmetric thermal LBE models; Then, under the single fluid assumption, a binary mixtures LBE model with MRT is proposed, which overcome the Schmidt and the viscosity problems in the existing LBE models; These theoretical works have provided a solid foundation for LBE to investigate the field of heat and mass transfer.(2) Application of the LBE to microscopic problems:Firstly, two different boundary conditions have been proposed, i.e, one is the combination of the equilibrium distribution and the specular refection scheme, and another is the combination of the equilibrium distribution and the bounce back scheme. Then, the heat and mass transfer problems in two or three dimensional microscopic pipe flows have been investigated, and a detailed analysis for the discrete effects on the boundary conditions is discussed, and correct treatment schemes are proposed; Finally, we applied the proposed models in (1) to investigating the microscopic gas flow of heat transfer problems, and mass transfer in Kramer or Poiseuille flows, and found that the MRT thermal model could capture the thermal creep phenomena;...