The Liquid Film Shrinkage Of Non-isothermal Falling Film Flow

Falling film flow,as one of the common flow patterns in industrial production,has been widely used in a variety of areas.Non-isothermal falling film flow is particular,which deserves deeply researching.In this thesis,the shape of non-isothermal falling film flow along the vertical plate was observed,and the mechanism of its shrinkage was analyzed.Besides,non-isothermal falling film flow on structured packing surface was observed through a visual experiment device.In the non-isothermal falling film with saturated steam and low temperature liquid flowing countercurrent,the film shrank dramatically with width decreasing along the vertical direction.With the decrease of liquid inlet temperature,the width and wetting area both decreased obviously,which became more significant at lower feeding rate.Temperature gradient existed for the temperature on the edge of the film being higher than that of the main body at the same horizontal height,which became more significant when the temperature difference between gas and liquid was large,matching the shrinkage degree well.There existed obvious difference after changing the surface tension gradient under different temperature with Tween 20 on the parameters such as film width and wetting area compared to the non-isothermal falling film with water.The larger the surface tension gradient was,the smaller the film width and wetting area were.And the difference became more obvious when the temperature difference between gas and liquid was large and the feeding rate was low.Combining with the result of the foregoing part,conclusion was summarized that surface tension gradient has great effects on the film shape forming progress,which meant Marangoni effect was the driving force of the shrinkage.Laser Induced Fluorescence(LIF)was used to observe the flow pattern of falling film on the structured packing surface,which enabled visualization as well as quantification of film properties.It showed that wetting area decreased with the increase of packing temperature,leading to dry plate phenomenon.The increase of local film thickness and formation of rivulet were captured by LIF as well.As a result,the shrinkage of non-isothermal falling film on structured packing surface is significant as well,which calls for enough attention to pay in industrial production.