Study On Micro Heat And Mass Transfer Process Of Flat Thin Liquid Film

With the shortage of fresh water resources and the development of the seafaring,ship seawater desalination has been widely concerned.At present,most of the research and analysis are concentrated in the macro field.The study of fluid motion in mesoscopic scale is of great significance for the analysis of micro heat and mass transfer in flat film heat transfer.Based on the background of ship seawater desalination,a plate liquid film heat transfer test rig is built to analyze the changes of temperature rise and heat transfer coefficient under different working conditions,The LBM method was used to establish the two-dimensional calculation model of the heat transfer of the flat film,and the heat and mass transfer processes inside the film were analyzed in detail by simulation,providing theoretical support on the mesoscopic scale for the micro flow of the flat film.The plate liquid film heat transfer experiment mainly analyzes the variation of temperature rise of the fluid and the variation law and reason of the fluid heat transfer coefficient under different initial temperatures and temperature differences.The numerical simulation mainly analyzes the distribution of velocity,temperature and concentration in the heat transfer process,and the influence of different initial temperatures and heating temperature differences on heat and mass transfer,the variation trend of velocity,temperature and concentration is analyzed.influence on fluid flow is analyzed under two conditions with and without phase change.The experimental results show that the film temperature increases linearly with heating time,and the increase rate of fluid temperature increases first and then decreases,and then increases.The variation trends of fluid temperature at different initial temperatures are consistent.The fluid temperature increases with the increase of heat flux.The heat transfer coefficient of the fluid increases with the increase of the initial temperature,increases with the increase of the heat flux,and decreases with the increase of the temperature difference,the larger the heat flux and the smaller the temperature difference are,the greater the heat transfer coefficient of the fluid is.The experimental results are in good agreement with the simulated values.The simulation results show that the film fluid is heated to form two symmetrical circulation flows,and the fluid gathers up in the middle and flows upward.The left fluid forms counterclockwise circulation flow,and the right fluid forms clockwise circulation flow.During the flow process,the fluid forms four velocity stagnation zones and two high-speed zones,which are symmetrically distributed around and up and down.The film temperature decreases gradually along the longitudinal direction,and changes slightly along the transverse section.The change curve shows an upward arch trend,and the temperature distribution of the left and right measurements is symmetrical.The concentration gradually decreases with the depth of the longitudinal direction,and the concentration changes at the same cross section show concave distribution,and the concentration of the fluid on both sides is symmetrically distributed.Both the increase of initial temperature and the increase of heating temperature difference increase the velocity,temperature and concentration to varying degrees,which strengthens the micro-motion of the fluid in the film and promotes the heat and mass transfer of the fluid.The variation trends of velocity and temperature of fluid with and without phase change are relatively consistent,and the occurrence of phase change will strengthen the fluid disturbance and enhance the heat and mass transfer of fluid.The experimental results are basically consistent with the simulation results in the temperature distribution along the transverse direction.The temperature of the fluid on both sides is low,and the temperature of the intermediate fluid is high.Due to the discontinuity and error of the experimental measuring points,the temperature measured by the experiment is not completely symmetrical,and the temperature of the fluid on the left side of the film is slightly higher than that on the right side.