Abstract:

Enhancement of the heat and mass transfer outside the tube of evaporative condensers can effectively reduce the energy consumption in a refrigeration system. The improving characteristics of heat and mass transfer outside a flat tube for evaporative condensers were investigated. Numerical simulation of the heat and mass transfer on the flat tube was carried out in Fluent using user define functions and component transport models. The heat transfer performance of a circular tube with the same perimeter was compared with that of the flat tube. The thickness and velocity of the liquid film outside the tube, the temperature distribution and the variation of moisture content outside the tube are studied, and the average heat transfer coefficients of the flat tube and the circular tube are compared. The results show that the average heat transfer coefficient of the flat tube is 9.04% higher than that of the circular tube. In addition, the influence of wind speed and spray density on the heat transfer of flat tube evaporative condenser is calculated. The wind speed varies from 1.5 m·s^-1 to 3 m·s^-1 and the spray density varies from 0.15 kg·m^-1·s^-1 to 0.3 kg·m^-1·s^-1. The results show that the average heat transfer coefficient increases by 5.68% and 30.26% respectively. Investigating the heat and mass transfer characteristics outside a flat tube for evaporative condensers provides theoretical guidance for the application of the flat tube in evaporative condensers.

Key words: evaporative condensers, flat tube, evaporation, heat transfer, mass transfer

摘要：

强化蒸发式冷凝器管外传热传质可有效降低系统能耗，利用Fluent软件，结合自编译程序及组分输运模型对扁管蒸发式冷凝器管外传热传质过程建模，选取了等周长圆管模型进行比较，研究了二者传热传质性能的差异。通过研究管外液膜厚度及速度，以及管外温度分布和含湿量的变化规律，对比了扁管和圆管的平均表面传热系数，结果表明扁管的平均表面传热系数于圆管提升了9.04%。模拟了风速从1.5 m·s^-1变化至3 m·s^-1以及喷淋密度从0.15 kg·m^-1·s^-1增加至0.3 kg·m^-1·s^-1时对扁管式蒸发式冷凝器换热的影响，得到随着风速及喷淋密度的增加其平均表面传热系数分别增加了5.68%和30.26%。对扁管式蒸发式冷凝器管外的传热传质特性的研究为其应用提供了理论指导。

关键词: 蒸发式冷凝器, 扁管, 蒸发, 传热, 传质