Experimental Study On The Flow And Fluctuation Of Falling Liquid Film On Vertical Heating Wall

The flow of liquid film on the vertical heating wall is widely used in various fields of industry,such as the cooling of the aerospace engine,the cooling of large-scale integrated circuits,the cooling of thermal power plants and nuclear power plants,the desulfurization,purification and extraction by using liquid film in chemical engineering and the vertical wall evaporator,film humidifier in life.But because the study of film related to fluctuations,flow and heat and mass transfer,as well as rupture,the study is not sufficient,further research is needed.This paper mainly studied the flow and fluctuation of the liquid film by using the observed experimental data through the construction of a liquid film flow test bench.The flow state and the fluctuating state of the liquid film were observed by a CCD camera and an external light source.The results showed that the liquid film flow gradually transitioned from laminar flow to turbulent flow as the Reynolds number increased,and the fluctuation state also increased with the Reynolds number increased.It is found that the degree of curvature of the corrugations is related to the Reynolds number,and the characteristic values of the formed horse-shoes waves within a certain Reynolds number range are measured,indicating that it has a stable interval.In addition,the liquid film is photographed from the side using a laser to obtain a two-dimensional outline of the flow direction of the liquid film.In this experiment,the white light confocal displacement sensor was used to measure the thickness of the liquid film.The advantage of this instrument is its high accuracy.The disadvantage is that it can only measure one point.The results show that even at small Reynolds numbers,the liquid film thickness changes slightly,but the thickness tends to be stable value.With the increase of the Reynolds number,the average thickness of the liquid film grows exponentially,and the thickness fluctuates more and more,the frequency becomes higher and higher,and the fluctuating displacement map and speed diagram are saw-like.When heated,the change in the thickness of the liquid film is promoted,and in some places,the thickness is significantly increased.In some cases,the liquid film thickness is significantly reduced.The data of the temperature of the liquid film measured by an infrared thermometer show that the temperature distribution of the liquid film is not uniform during heating,and the nonuniformity becomes larger as the heat flux density increases;the temperature distribution of the liquid film is a stripe distribution The temperature in some region is high and but another is low,and due to the marangoni effect caused by this temperature distribution,the liquid film in the high temperature region moves to the liquid film in the low temperature region,so that the liquid film thickness distribution is not uniform.The temperature cloud diagrams under different Reynolds number conditions show that the distribution of liquid film temperature location is not significantly related to the Reynolds number.When the Reynolds number is small,and the heat flux density is large,the liquid film is prone to cracking,and the cracked part is likely to occur at a high temperature edge position.