Experimental Study On Liquid Column Separation Distance And Splash Volume In Falling Film Flow

Horizontal tube falling film evaporation is a highly efficient and energy-saving heat transfer technology,which is widely used in desalination,petrochemical,refrigeration and other fields.The heat transfer process includes two parts:the condensation of steam in the tube and the evaporation of the liquid outside the tube,and it is a very complex heat and mass transfer process.The fluid flow and spread outside the tube,the formation of the liquid film and the distribution of film thickness,the fluctuation of the fluid and the splash of the liquid,they all have great influence on the heat and mass transfer process.Therefore,it is very necessary to study the flow characteristics of the falling film,and has a great practical significance.The flow characteristics of the liquid film outside the horizontal tube were studied by numerical simulation.The distribution of the film thickness outside the horizontal tube with the circle angle is analyzed,and the influence of the spray density,the diameter of the pipe and the height of the cloth on the film thickness is studied.The results show that with the increase of the circle angle,the thickness of the liquid film shows the trend of decreasing first and then increasing.Under the same conditions,when the spray density increases,the thickness of the liquid film at the same position outside the tube becomes larger.With the increasing of the spray height,the thickness of the outer liquid film shows the decrease trend.In the case of a certain height and spray density,the thickness of the liquid film at the same position outside the tube tends to decrease gradually as the tube diameter increases.The falling film flow experimental bench was built.The influence of spray density,pipe diameter and tube spacing on the flow pattern of the tube was studied.The distribution and influence factors of the separation distance of the column in the column flow pattern under different diameter and tube spacing are studied.The droplet splashing in the column flow pattern and its influencing factors are also discussed.The results show that the separation distance of the column under the columnar flow is not a fixed value,and is variable with the changing of the parameters such as pipe diameter and tube spacing.But the overall values agree well with the theoretical value,validated the accuracy of theoretical prediction.The droplet splashing in the columnar flow pattern is affected by a number of factors: as the spray density increases,the amount of liquid splash increases gradually.As the spacing of the tubes increases,the height of the liquid drop becomes high,resulting in a stronger impact ofthe liquid droplets or liquid column on the liquid film and an increase the amount of liquid spatter.As the diameter increases,the surface area of the fluid spreading on the outer surface of the tube increases,resulting in thinning of the film thickness of the outer surface of the tube.When the liquid droplets or liquid column impact liquid film,the thickness of the liquid film will also affect the amount of spatter.