REV-Scale Study Of Flow And Heat Transfer Enhancement Of Porous Media Based On Lattice Boltzmann Method

The flow and heat transfer in porous media is a common natural phenomenon, application of which is related to many domains such as chemical engineering, oil ex-ploitation, irrigation and water conservation project and so on. The fluid flow control and heat transfer enhancement are two key questions in the field of flow and heat trans-fer. It is well documented that the porous media can be used in fluid flow control and heat transfer strengthen. However, few systematic research has been carried out on its physical mechanism. With the rapid development of the computer technology, the advantages of numerical simulation become more prominent and receive increasing at-tentions. The numerical study on the fluid flow and heat transfer in porous media can be classified into two classes:the pore scale type and the REV (Representative Elementary Volume) scale one. The main works of this thesis are based on REV scale simulation.As a new numerical method, LBM (Lattice Boltzmann Method) is very suitable for studying flow and heat transfer in porous media. However, the exiting models still have some insufficiencies and the improvement are still needed. For example, no axisymmetric LBE mode for flow and heat transfer in porous media can be found. The aim of this thesis is to develop some new LB models for flow and heat transfer in porous media, and then applied them to study the flow control and heat transfer in porous media.Theory of the LB models:(1) This paper presents a kind of of axisymmetric thermal LBE model for flows through porous media. The model is similar to the standard LBE model and has a simple structure. Another advantage of the present model is that the simple force term in evolution equations makes the computation more effective and stable.(2) This paper presents a kind of axisymmetric LBE model for incompressible flows through porous media. In the model, distribution function is constructed based on the pressure instead of the fluid density, so that the compressibility is reduced ef-fectively. A improved method is proposed to deal with the external forces, which can overcome the difficulty of calculate the the fluid velocity and pressure. Applications of the models to flow in porous media:(1) The flow around a porous covering square cylinder in a channel has been stud-ied. The effects of several parameters on flow field are discussed. The numerical results show that the influence of porosity on the flow field, drag and lift coefficient is neglectable, whereas the effect of Darcy(Da) number is dominant.(2) Rayleigh-Benard convection with temperature-dependent viscosity in a porous cavity has been studied. The effects of several parameters on flow and heat transfer are studied, the results show that the influence of viscosity is very important. A new reference temperature based on linear fitting function is proposed, which is proved to be more efficient in the average Nusselt numbers computations.(3)The effect of heat transfer in a pipe partially filled with porous media is inves-tigated using our proposed axisymmetric thermal LBE model for flows through porous media. A Graphic Processing Unit(GPU) is applied to overcome the poor computa-tional efficiency of CPU. The numerical results show that filling porous media in the center of pipe can enhance the heat transfer while increase flow resistance. A balance between heat transfer and flow resistance reduction should be emphasized in practice.In conclusion, the fluid flow and heat transfer in porous media at REV scale is investigated via LBM, and many valuable efforts are made. Two kinds of lattice Boltzmann models are proposed to solve the axisymmetric flow in porous media. In addition, a large number of numerical simulations are conducted to study flow and heat transfer in porous media and a series of significative conclusions are gained through the analyses. These works can be viewed as a necessary basis for future studies.