环形布膜器垂直管内R113降膜蒸发换热特性数值研究

摘要

By establishing physical and mathematic model for R113 falling film evaporation in vertical tube of an annular membrane evaporator,two-dimensional unsteady numerical simulation was conducted on heat transfer characteristics of the gas-liquid countercurrent falling film evaporation,so as to analyze the distribution of liquid film flow,wall temperature and film surface temperature,and to compare the thickness of liquid film before and after heating.Results show that in the process of falling film evaporation,the splash of droplets starts from the lower end of liquid film,which propagates gradually toward the upper end;for R113,both the wall and film temperature rise along the flow direction during falling film evaporation,while the gas temperature falls;the temperature reduces gradually from wall to center along the radial direction,and the temperature distribution tends to be opposite at the position 1 mm away from the wall;the thickness of liquid film reduces greatly after heating,when the thickness of downstream film becomes relatively uniform.%通过建立垂直管内降膜蒸发物理数学模型,对环形插头型布膜器管内R113的气液两相逆流降膜蒸发换热特性进行二维非稳态数值研究,分析了管内液膜流动分布以及壁面温度和液膜表面温度分布,对比了加热前后液膜厚度的变化.结果表明:随着降膜蒸发过程的进行,液膜下端开始出现液滴飞溅,且不断向上端发展;R113在管内降膜蒸发过程中壁面温度和液膜表面温度沿流动方向逐渐升高,气相温度变化趋势则相反;从壁面到管中心,温度沿径向逐步降低,在近壁面1 mm前后其分布趋势相反;加热后液膜厚度明显减小,且下游液膜厚度变得相对均匀.