水平管降膜蒸发器管外膜状流流动特征研究

Study of Sheet-Flow Characteristics Outside Tube of Horizontal Tube Falling Film Evaporator

为了探究水平管降膜蒸发器管外液膜分布的优劣对其传热性能的影响,课题组建立了水平管三维模型对管外膜状流流动进行数值模拟,得到液膜沿水平管轴向和周向的分布规律,并对膜厚波动幅度Δ进行研究;分析了流量、布液高度及管外径对管外液膜厚度的影响。结果表明:当周向角度一定时,液膜厚度沿水平管轴向小幅波动;膜厚波动幅度Δ在θ为10°~20°时逐渐减小,其最大值为0.16862;在θ为150°~170°时逐渐增大,其最大值为0.36291;当θ为20°~150°时,膜厚波动幅度Δ<0.07500,液膜流动呈现平稳发展的趋势。研究表明液膜沿水平管周向流动可划分为3个区域:θ为10°~20°时为冲击区,θ为20°~150°时为稳定区,θ为150°~170°时为尾流区。液膜厚度随流量的增大而增大,随布液高度和管外径的增大而减小。

In order to investigate the influence of outer liquid film distribution of the horizontal tube falling film evaporator on its heat transfer performance,a three-dimensional model was established to numerically simulate the sheet-flow outside the tube of horizontal tube falling film evaporator.The distribution law of liquid film along the horizontal tube in axial and circumferential directions was obtained,and the fluctuation amplitude of film thickness was studied.The effects of flow rate,distribution height and outer diameter of tube on the film thickness outside the horizontal tube were analyzed.The results show that when the circumferential angle is constant,the liquid film thickness slightly fluctuates along the axial direction of the horizontal tube.The fluctuation amplitude of film thickness decreased gradually atθ=10°~20°and increased atθ=150°~170°,with the maximum value of 0.16862 and 0.36291 respectively.Whenθ=20°~150°,the fluctuation amplitude of film thickness is less than 0.07500,and the liquid film flow showed a steady development trend.The circumferential flow of the liquid film along the horizontal tube can be divided into three zones:the impact zone atθ=10°~20°,the stable zone atθ=20°~150°and the wake zone atθ=150°~170°.The liquid film thickness increases with the increase of flow rate and decreases with the increase of distribution height and outer diameter.