水平管外降膜传热性能的数值模拟及实验研究

Numerical Simulation and Experimental Study on Heat Transfer Performance of Falling Film outside the Horizontal Tube

采用数值模拟和实验方法,研究了水平管降膜蒸发器换热管间为柱状流时管外降膜传热性能。利用Fluent软件对管外液体流动和传热过程进行模拟,得到液膜表面速度、管外壁面局部传热系数的分布规律,分析了喷淋密度和管间距对传热性能的影响,最后对比了数值模拟结果和实验数据。结果表明:液柱的冲击和管底液体汇聚产生的扰动明显提高了传热性能;传热系数最大值出现在液柱冲击换热管形成的滞止区,在换热管下半周传热系数变化较小,传热性能比较稳定;管外传热系数随着喷淋密度的增加而增大;当轴向无量纲距离L在-0. 3～0. 3区域时增加管间距对管外传热有利,但在0. 4～0. 5和-0. 5～-0. 4区域时传热系数随着管间距的增大而减小。实验结果验证了数值模拟的可靠性。

Having numerical simulation and experimental methods adopted to investigate the falling film’s heat transfer performance outside tubes of the horizontal tube evaporator with columnar flow there was implemented,including having the Fluent software used to simulate both the flow and the heat transfer process of the liquid outside tubes so as to obtain velocity of liquid film surface and distributions of local heat transfer coefficient over the outer wall of the tube.Effects of spray density and tube spacing on the heat transfer performance were analyzed and the numerical simulation results were compared with the experimental data to show that,both impingement of the liquid column and disturbance caused by convergence of liquid at bottom of the tube can significantly improve heat transfer performance;the maximum heat transfer coefficient appears in the stagnation zone formed by the liquid column impacting;the heat transfer performance is more stable around the low-half tube;the coefficient of heat transfer outside the tube increases with the growth of spray density;increasing the tube spacing is beneficial to heat transfer outside the tube when the axial dimensionless distance( L )-0.3≤L≤0.3,but the heat transfer coefficient decreases with the increase of tube spacing in the range of 0.4≤L≤0.5 and-0.5≤L≤-0.4.Experimental results verify the reliability of the numerical simulation.