液氮减压制冷系统中干式过冷器换热特性分析

Heat transfer characteristics of dry-type subcooler in liquid nitrogen decompression refrigeration system

本文针对干式过冷器换热特性问题,选择合适的经验关系式对过冷器性能进行预测,探究了管径对换热性能的影响规律,并对杜瓦内过冷液氮的自然对流换热进行数值仿真分析,进而研究了变工况下制冷系统工作特性。结果表明,管径减小时管内沸腾换热系数显著增大而管外自然对流换热系数增长幅度较小,过冷器的主要热阻在管外自然对流侧,杜瓦内过冷液氮温度主要在竖直方向和径向上变化,热源壁面附近较大的温度梯度表明热源与液氮间热阻较大,变工况工作时温度指标与系统热负荷及过冷器壁温均近似呈现线性正相关关系。

In this work, aiming at the heat transfer characteristics of the dry-type subcooler, suitable empirical relations were selected to predict the performance of the subcooler, and the influence of the pipe diameter on heat transfer performance was studied. The natural convection of liquid nitrogen in Dewar was analyzed by numerical simulation, and the working characteristics of refrigeration system under variable working conditions were studied. The results show that, with the decrease of the tube diameter, the boiling heat transfer coefficient inside the tube increases significantly while the natural convection heat transfer coefficient outside the tube increases much less. The main thermal resistance of the subcooler is in the natural convection zone outside the tube. The temperature of the subcooled liquid nitrogen in Dewar mainly changes in the vertical and radial directions, and the large temperature gradient near the heat source wall indicates that there is a large thermal resistance. Under variable working conditions, temperature indicators show approximately linear positive relationship with the change of heat load and with the change of subcooler wall temperature.