Regulation Strategy Of Bubble Transportation In Porous Medium Based On Lattice Boltzmann Method In Pore Scale

Bubble transportation through porous medium is widespread in various fields in nature and engineering process.Reasonable configuration of porous structure's parameters can accelerate the transportation velocity of bubbles through the porous medium,which is of great significance on the improvement in the gas-liquid two-phase flow,heat exchange process and the process optimization.However,at present,researchers pay more attention to bubbles' motion characteristics itself,and most researches are conducted on two-phase flow through the simple channel structure or around the solid obstacle.The study on the influence of the structure and the wetting characteristics of the porous medium on bubble transportation is rather less.Lattice Boltzmann method(LBM)as a mesoscopic simulation method has unique advantages in dealing with complex boundary problems and multiphase flow processes.In this paper,the transport characteristics of bubbles in porous medium are studied by Lattice Boltzmann method based on the background of the capillary transportation process.The main content of the thesis is as follows.By using Lattice Boltzmann method,a flow model in the porous medium is established.The model is verified by case calculation including Maxwell construction theory,surface tension,wall wettability,and morphological characteristics of the rising bubble.The simulation results are in good agreement with the literatures'.Based on the transportation of bubbles through the pores of porous medium,the effects of the porosity,the wetting characteristics of the porous medium,the arrangement of the channels and the bubble's initial velocity in the horizontal direction on the bubble morphology,rising speed,average contact area with the wall and capillary force were discussed.By comprehensively weighing the time of the bubble passing through the porous medium,the contact area with the wall surface,and the capillary pressure of the channel,etc.,the design range of the porosity and the selection basis of the channel arrangement are obtained.In addition,it is found that the wall wettability has a significant effect on the bubble transportation characteristics.The strategy is also obtained that the bubbles with a certain initial velocity in the horizontal direction during the actual evaporation process could escape from the porous medium more quickly.The simulation of the transportation of bubbles on the wettability gradient surface was implemented based on transport regulation for bubbles in complex porous medium.It was proved that the wettability gradient structure can realize the spontaneous transportation of bubbles.And the influence of different wettability gradients and bubble sizes on the bubble transportation process were analyzed.Two types of wettability combination porous structures were designed to explore the transport characteristics of bubbles under different porosity and wettability.In addition,the wettability combination structure is improved to wettability gradient porous structure.The self-driven effect of different wettability gradients on the bubble transportation process was studied,and the porous structure most suitable for capillary transport process was obtained.The reason for bubble spontaneous transportation and the decrease in resistance during the transportation was demonstrated by force analysis of the bubble.It provides relevant theoretical foundation and design consideration for pores' fabrication of porous medium in the capillary transportation process.