The Lattice Boltzmann Simulation Of Gas Flow And Heat Transfer In Compact Porous Media

With the arising of the practical problem of using greenhouse gas to improve oil recovery in low-permeability reservoirs, research for the permeability of densely porous medium is receiving more and more attention. Today, flow and heat transfer of gas in the densely porous medium has become a very hot area of research. In such low-permeability porous medium, the pore-channel size, which is comparable to the mean free path of gas molecules, is so small that Knudsen is ralatively large. In these microflows,there will be both velocity slip and temperature jump. And classical Navier-Stokes equations and Fourier law with nonslip boundary condition is never suitable for this kind of gas flow and heat transfer with high Kn, because continuity assumption does not hold now. Fortunately, Boltzmann equation, without the introduction of continuity assumption, can be uesed to simulate the flow and heat transfer of rarefied gas from continuum region to free-molecule area. The lattice Boltzmann method, which has developed well on the basis of gas dynamics recently, is regarded as a strong tool to simulate the complex microflows and heat transfers for its advantages, such as the simplicity of program, location of computation, natural parallel and the ability to deal easily with the complex boundary conditions in the porous medium.In this thesis, the lattice BGK models and boundary conditions proposed by some scholars are applied to simulate the flows and heat transfers in porous medium. Specific work are:One, in considering the interaction between fluid and the wall, we give the correct expression of relaxation timeÏ„from Kn. Through appling the single-channel micro-scale lattice Boltzmann model proposed by Guo et al. to flows in pore group, we simulate the percolation of gas in two simplified porous media and study some basic percolation mechanism;Two, based on the double-distribution thermal model and using the microscale thermal lattice boundary method proposed by Zheng et al., we simulate the flows and heat transfers of four kind of gases, such as CO₂ and N₂, in two simplified porous media, and then compare the mass flux, the heat flux and the temperature jump along the wall of each gas.In short, we have studied a number of flow and heat transfer problems in dense porous media through lattice Boltzmann method. The simulation results are verified based on theoretical analysis and experimental results of the literatures. This work are useful in guiding oil recovery with greenhouse gas CO2 and performance enhancement of heat exchangers. Meanwhile, it shows that the Lattice Boltzmann method can serve as a promising tool for simulating gas flows and heat transfers through a compact porous medium.