场协同原理强化管外降膜吸收传热特性实验研究

Experimental investigation of falling film absorption heat transfer performance for field synergy principle enhanced tubes

对基于场协同原理设计的两种强化传热管型进行了LiBr降膜吸收水蒸气过程的传热实验研究,并与光滑铜管作比较,考查该传热管型在吸收过程中的强化作用.实验测量参数包括:溶液进出口温度、浓度、流量,冷却水进出口温度、流量等.实验结果表明,两种强化传热管型在低雷诺数时对LiBr降膜吸收传热的强化比分别为20%和50%,而且随着雷诺数的增大而增大.利用场协同理论和降液膜流动的波动特性分析了强化降膜吸收过程传热特性的物理机制,发现速度矢量与温度梯度的夹角及降液膜厚度形成的阻力对对流换热有一定影响.

The falling film absorption heat transfer of water-lithium bromide on the outer surface of vertical tubes is experimentally studied. The two enhanced heat transfer tubes are designed in terms of the field synergy principle. Their absorption heat transfer performance is compared with that of the smooth copper tube as well to investigate the enhancement effect in absorption process. The control variables for the experimental study were solution mass flow rate, solution concentration and temperature, cooling water temperature and mass flow rate. The experimental results indicate that two heat-enhanced tubes can considerably improve the LiBr/H20 falling film absorption performance. The heat transfer enhancement ratios for the two tubes are 200/6 and 50 % respectively at lower falling film Reynolds number, and increase with the Reynolds number of cooling water. The inherent physical mechanism of heat transfer enhancement is analyzed with respect to the field synergy principle and the wavy nature of the falling film. It is discovered that both the intersection angle between velocity and temperature gradient and the heat resistance caused by film thickness have an effect on convective heat transfer.