水平管降膜管间流态的数值模拟

Numerical Simulation Analysis on Falling Film Flow Pattern between Tubes

目的研究水平管外液膜流动状态的转变规律,模拟分析流量、管径、管间距等对管间流态的影响和液体对管壁的润湿程度.方法建立水平管降膜流态数学模型,通过fluent软件进行模拟计算,分析水平管间溴化锂溶液流态转变过程.结果溴化锂溶液比水具有更好的布膜效果和稳定性.当水平管临界值Re≤34时,管间流态为滴状;34<Re≤122时,管间流态为柱状;当122<Re≤219时,管间流态为帘状.流动区时间t=0.02 s为自由下落区、t=0.04 s为冲击区、t=0.05 s为发展区、t=0.08s为充分发展区、t=0.1 s为尾流区,圆管的顶部区域会出现压力的最大值,而速度的最大区域出现在圆管的下半部分的充分发展区.管径为14 mm的圆管完全润湿的最小流量为0.01 L/s.结论随着管间距或管径的增加,管间流态向上一级流态转换.管间距增加,流态为滴状时无明显变化,流态为柱状时两管之间流体变细,流态为帘状时不能形成稳定连续流体,随着流量的增大,形状的变化越明显.其结果可为蒸发器、冷凝器、除湿器等热质交换设备的设计和性能研究提供理论指导.

In this paper,a mathematical and physical model for falling-film-type horizontal-tube was established in the hydro kinetics calculating software called Fluent to simulate the effects of film flow pattern and wetting condition outside horizontal tubes. The solution of lithium bromide and water were selected as spray liquid. With numerical simulation by observing the flow pattern of liquid film,the conversion regularity of flow pattern are studied and the three critical value of flow pattern in the droplet,the columnar and the sheet were obtained,by debugging different flow rate,the minimum flow rate which wet the whole tube wall was obtained,by changing of pipe diametermaterial,tube pitch and solution properties,etc,the change regularity of flow pattern was obtained between tubes. The results show that when Re less than 34,the flow pattern was droplet,when Re between 4 and 122,the flow pattern was columnar,when Re between 122 and 219 the flow pattern was sheet,and the minimum flow rate was 0. 01 L /s. The appears time of the free fall area,the impact area,the development area,the full development area and the wake area were 0. 02 s,0. 04 s,0. 05 s,0. 08 s,0. 1s respectively and the maximum area of velocity and pressure were the impact area and the development area respectively. The flow pattern can be transformed into one or more levels of former with the increase of pipe diameter or tube pitch. The research result has an effect on developing heat and mass transfer model and experimental analysis.