Systematic Research on Free Convection Heat Transfer in a Stably Stratified

为了对稳定分层流体中的自由对流换热进行系统的研究，本文对以下三个问题进行了研究。内筒直径对同轴筒间自由对流换热的影响用蔗糖水溶液形成层状层，外筒加热(直径70 mm)。恒定热流并从内筒冷却(直径15 mm、30 mm或50.8 mm)。在恒温下。结果表明，内筒尺寸对早期换热有影响，当内筒直径变大时，其对流换热表现出与竖板间相似的换热特性。当内筒直径较小时，平均换热系数随时间接近稳态值，但不会超过稳态值。换热板间距对竖板间自由对流换热的影响分层层用蔗糖水溶液形成，从一侧壁恒定热流加热，从另一侧恒温冷却。分别对L=10 mm、40 mm、60 mm的换热板间距进行了实验，并与作者报道的L=20 mm的实验结果进行了比较。结果发现，当泡沫层厚度等于换热板之间的距离时，平均换热系数变大。对矩形单元内的自由对流换热进行了数值分析，得到了长径比为0.1~20、Ra数为10~3~10~7的宽幅范围内矩形单元内的自由对流换热，并建立了换热系数的关联式，建立了稳定分层流体中换热的理论模型。

The following three issues have been investigated to conduct a systematic research on free convection heat transfer in a stably stratified fluid.1. Effects of the inner cylinder diameter on free convection heat transfer between coaxial cylindersThe stratified layer was formed using a sucrose aqueous solution, and was heated from the outer cylinder (70mm I.D.) at constant heat flux and cooled from the inner cylinder (15mm, 30mm or 50.8mm O.D.) at constant temperature. As a result, it is found that the early stage heat transfer is affected by the size of the inner cylinder, and the convection heat transfer shows similar characteristics of that between vertical plates, when the inner cylinder diameter becomes large. On the other hand, when the inner cylinder diameter being small, the average heat transfer coefficient approaches the steady state value with time but never exceeds it.2. Effects of a distance between heat transfer plates on free convection heat transfer between vertical platesThe stratified layer was formed using a sucrose aqueous solution, and was heated from one side wall at constant heat flux and cooled from the other side wall at constant temperature. The experiments were conducted for the distance between the heat transfer plates l=10mm, 40mm and 60mm, and the results were compared with those for l=20mm which are reported by the authors. As a result, it has been found that the average heat transfer coefficient becomes great, when the cellular layer thickness equals to the distance between the heat transfer plates.3. Numerical analysis on free convection heat transfer in a rectangular cellNumerical analysis has been performed on free convection heat transfer in a rectangular cell for wide rages of aspect ration 0.1-20 and Ra number 10^3-10^7, and correlation equations for the heat transfer coefficient have been developed to construct a theoretical model for analyzing the heat transfer in a stably stratified fluid.