LBM Simulation Of Surface Evaporation In Porous Media By Air Gap Diffusion Distillation

With the development of human society,the demand for fresh water resources is increasing,and the fresh water resources on earth are rapidly consumed.Using seawater desalination technology is an important technical means to solve the imbalance between supply and demand of fresh water resources and the shortage of fresh water resources between regions.Using porous media as an evaporator in an air gap diffusion distillation device can effectively reduce the economic cost of the device and increase the yield of fresh water.An in-depth understanding of fluid flow heat transfer and surface evaporation in porous media can provide an important theoretical basis for improving freshwater production and energy utilization efficiency in air gap diffusion distillation device.The single-phase lattice Boltzmann model and phase-change lattice Boltzmann model are used to study the flow heat transfer of single-phase fluid in porous media and the evaporation of liquid on porous media surface respectively in this study.A new wetting boundary scheme is introduced into the phase-change lattice Boltzmann model and verified by the static contact angle of a two-dimensional cylindrical surface,which effectively improves the accuracy and stability of the contact angle.The single-phase lattice Boltzmann model is used to investigate the flow and heat transfer of single-phase fluid in porous media.In the flow in accordance with Darcy’s law,the heat transfer between hot fluid and cold wall increases gradually with the decrease of porosity.It is found that the more consistent the fluid flow direction is with the heat transfer direction in the porous media,the better the heat transfer effect is.The higher the flow velocity of the fluid in porous media,the better the heat transfer between fluid and cold wall surface.However,with the increase of inlet velocity,the fluid mass in porous media increases and the average outlet temperature decreases.Surface evaporation of porous media is studied by using the phase-change lattice Boltzmann model.For surface evaporation of horizontally placed porous media,when the surface area of the porous media skeleton is constant,the size of transverse and longitudinal pore size can change the size of the vapor-liquid contact surface of porous media,and then affect the evaporation rate of the porous media surface.When the porous medium is hydrophilic,the surface evaporation rate can be increased by reducing the contact angle of the porous media skeleton.When the distribution and shape of porous media skeleton are the same,increasing the thermal conductivity of porous media skeleton can effectively improve the evaporation rate of liquid.For the surface evaporation of vertically placed porous media,when the inlet velocity of liquid in the porous media is the same,increasing the thickness of the porous medium will reduce the evaporation of liquid.When the thickness of porous media is the same,the evaporation rate does not necessarily increase when the inlet velocity of porous media increases,which depends on the distribution and flow state of liquid in porous media.Changing the arrangement of the skeleton in the porous media,the porous media with a forked row has a higher amount of evaporation than the porous media with a straight row at a low flow rate.