Numerical Investigation Of Heat And Mass Transfer In Multiple Phases And Components Flows Using Lattice Boltzmann Method

Lattice Boltzmann method(LBM) has recently begun to receive considerable attention as a possible alternative to conventional computational fluid dynamics(CFD) for simulating fluid flow.These algorithms have shown great promise for simulating flow in topologically complicated geometries,such as those encountered in porous media,and for simulations of multiple components or multiphase flow with heat and mass transfer,where there are few viable alternatives using conventional CFD method.Based on the lattice Boltzmann method,the research work focuses on the numerical investigation of heat and mass transfer in flows with multiple components and phases encountered in the rotating packed-bed and nucleate pool boiling,as follows:Using the lattice Boltzmann method ofmulticomponent flows,the liquid mass transfer in the forced convection and diffusion resulted by the column wire packing was simulated in the rotating packed-bed.By introducing a function which reflects the efficiency of the mixing,the relationships were analyzed and compared for the liquid mass transfer and the role of the convection in the wire packing with different size and form.Numerical simulation results can be considered as available data for improving the design of the packing and for studying on the mass transfer in the rotating packed-bed.The Lattice Blotzmann scheme for the serial competitive reaction is constituted.Based on the layer model that describes the reaction-diffusion without convection,the serial competitive reaction in the central zone of the Rotating Packed-bed is simulated.Its numerical results show the quantitative agreement with that in Ref.1 and demonstrate the scheme is efficient.Analyzing the experimental work in ref.1 and a model is developed to describe the reaction-diffusion with the forced convection resulted by the Packing wire.The model is suitable for study the mass transfer in the forced convection at the edge of the Rotating Paced-bed and is founded on a hypothesis that the several times larger size liquid is continue media than of the Packing wire.Applying the LB scheme the serial competitive reaction at the edge of the Rotating Packed-bed is simulated and the mass transfer in the forced convection resulted by the Packing wire is studied.Its results provide reference for the study on the scattered mass-transfer and the design of the Rotating Packing-bed.A parameter is added into lattice Boltzmann thermal models so that the models possess second-order accuracy.The models are employed to simulate the Rayleigh-Benard convection heat transfer for identifying abilities and are compared with its original model.As a result,it was found that there is error of computed Nu numbers for all three models when the Ra number and the thermal diffusivity become very bigger.After analyzing truncation error of the corresponding heat-transfer equation in macro scale,an adjusting parameter is introduced into the equilibrium distribution function in the paper.As a result,the computed error of the Nu number is eliminated by applying the parameter to adjust the coefficient of the truncated error.Improvements mentioned above show that the LBM heat-transfer models extends its simulation range and boosts up its applicability.Combining with the lattice Boltzmann thermal model,the lattice Boltzmann multiphase model with a large density ratio can be extended to describe the phenomenon of phase change with mass and heat transferring through the interface.Based on the Stefan boundary condition, the phase change is considered as change of the phase order parameter and is disposed as a source term of the Cahn-Hilliard(C-H) equation.The change of the interfacial position with the time is obtained as a part of the solution of the combined lattice Boltzmann equations. This hybrid model is applied to simulate the motion and growth of a vapor bubble as it rises through a uniformly superheated liquid.At the same time,parametric studies affected on the bubble growth,deformation and rising in the different surface tension forces and kinetic viscosities are also presented.Improving the Briant's treatment of the partial wetting boundaries,the hybrid model is applied to simulate the growth and departure of the single vapor bubble on the superheat wall. The numerical results exhibit correct parametric dependencies of the departure diameter as the experimental correlation in recent literature and show the hybrid model is suitable and feasible.On this basis,parametric studies on the growth,coalescence and departure of the twin-bubble on the horizontal wall are also presented.The content about thesis chapters is arranged as follows:The research background and the LBM review are summarized in Chapter 1.The LBM principle and its boundary treatment are introduced in Chapter 2.The numerical investigations and its results are presented in Chapter 3,4,5 and 6,respectively.The conclusions and prospect are provided in Chapter 7.