【摘要】 对自然对流条件下水平表面的初始结霜过程进行了实验研究.在壁温为-34～-19℃范围内,利用显微镜对霜层成长过程进行了一系列显微观测,应用双曝光全息干涉法测量了霜层表面温度和周围温度分布,还测量了通过冷壁面的热流密度和霜层厚度随时间的变化.获得了霜层有效导热系数和霜表面与环境空气间的自然对流传热系数,并关联为准则关系式.霜层初始成长阶段与充分成长阶段有着显著不同的特性.随着霜层的形成和成长,霜层表面温度逐渐升高,霜层厚度增加速率减缓,有效导热系数迅速降低,自然对流传热系数也减小.冷壁面温度低时,自然对流传热系数较大,霜层成长初期厚度增加也较快,但对有效导热系数影响不大,仅为冰导热系数的117%～17%.更多还原

【Abstract】 An experimental investigation was carried out on the characteristics of the frost layer during the initial growth period which developed on a cold flat plate under natural convection conditions. The cold plate temperatures were varied in the-34 to-19 ℃ range. A series of microscopic observation was conducted with the aid of a video microscope. The frost-air interface temperature and the temperature distribution above the interface were measured by employing two-exposure holographic interferometry technique. The heat flux on the plate and the variation of frost layer with time were also measured. The effective thermal conductivity of frost layer and the natural convective heat transfer coefficient were obtained based on the experimental measurements in the present study. An empirical correlation for the heat transfer coefficient was obtained. The significant difference of characteristics between the initial growth period and the full growth period was found. With the growing of frost layer in the initial growth period, the frost surface temperature is gradually increasing, and the frost growth rate, the effective thermal conductivity and the natural heat transfer coefficient are decreasing. The heat transfer coefficient and the frost growth rate are increasing with the decreasing of the cold plate temperature, while the influence on the effective thermal conductivity is not remarkable. The effective thermal conductivity is the ice thermal conductivity of 11.7 % to 1.7 %.更多还原