不同压力环境下竖直平板表面自然对流散热实验

飞行器从地面上升到太空的过程中所经历的大幅度环境参数变化,会导致飞行器及机载设备出现"超热"、"过冷"和"热分层"等现象。为得到不同环境压力下的关键参数--自然对流换热系数,本文搭建了一个能提供不同气压和环境温度的封闭试验舱,对在不同压力环境(0.0001,0.01,0.1,0.2,0.5,1,10,50 kPa和常压)下几种固定加热量(75,150,300 W/m²)的竖直平板散热进行了实验研究,通过对辐射散热和对流散热的分析比较,获取不用工况下气体的对流换热系数。结果表明:对流换热系数在绝对气压小于1 kPa时非常小,可以视作为0;在绝对气压大于1 kPa时,对流换热系数随压力的升高呈2次方增加;通过对环境物理参数的无因次化处理,得到的准则式方程可用于1~100 kPa的环境压力。

Experiment on surface natural convection heat transfer of vertical plate under different pressures

When rising from the ground to space, aircraft will experience substantial changes in environmental parameters, which leads to the emergence of "super-hot", "super-cold" and "thermal stratification" phenomenon of aircraft and airborne equipment. The objective of the present study is to obtain the key parameter-free convection heat transfer coefficient under different environmental pressures. In this study, experiments are carried out under different pressure conditions (0.0001, 0.01,0.1, 0.2, 0.5, 1, 10, 50 kPa and atmospheric pressure) and different constant heat input (75,150, 300 W/m²) to measure the heat transfer of vertical plate. Then convection heat transfer coefficient can be obtained under different conditions by comparing heat loss between radiation and convection. The results indicate that:convection heat transfer coefficient is pretty low when absolute pressure is less than 1 kPa, which can be regarded as zero; when the absolute atmosphere is higher than 1 kPa, square relation is found between increasing convection heat transfer coefficient and increasing pressure; by processing environmental parameters with dimensionless method, the obtained criterion equation can be used between 1 kPa and 100 kPa.