跨温区直接蒸发冷却的热质传递特性

Characteristics of heat and mass transfer in direct evaporative cooling process in different temperature ranges

低温干燥空气直接蒸发冷却用于制备低温冷水甚至冰晶时会跨越常温和低温两个温度区间,其传热传质特性会随温度区间而发生变化。进行了常温工况和非常温工况下氧化铝(Al2O3)泡沫陶瓷填料的逆流直接蒸发冷却实验,重点对0～15℃的非常温区间进行研究,对非常温区间的传热驱动力与蒸发冷却效率、传质驱动力与空气含湿量增量、焓差驱动力与焓效率之间的关系进行了定量的计算分析,并对比了常温与非常温工况下的直接蒸发冷却过程。在此基础上,利用分析方法对非常温工况下的能量利用价值进行了计算,并对其性能的提升和应用潜力进行了分析。

The characteristics of heat and mass transfer between the air and water in a direct evaporative cooling process will be different in different temperature ranges.In this study,experiments of a novel direct evaporative cooling counter-flow system were carried out with a psychrometric chamber in normal and lower temperature ranges.Experimental results show that a cooling efficiency of 88% can be achieved,demonstrating that the alumina foam ceramic is a promising packing material for the evaporative cooling system.The comparison of characteristics between normal and lower temperature ranges shows that direct evaporative cooling process in the lower temperature range is more sensitive to driving forces.In the temperature range from 0℃ to 15℃,the relationships between temperature difference and cooling efficiency,pressure of water vapor and air humidity difference,enthalpy difference and enthalpy efficiency were analyzed and determined.Exergy analysis was used to evaluate the energy effectiveness of direct evaporative cooling process in the lower temperature range,the improvement on performance,and application potential.