Systematic Research on Free Convection Heat Transfer in a Stably Stratified

本文围绕以下三个问题对稳定分层流体中的自然对流换热进行了系统的研究.内圆柱直径对同轴圆柱间自然对流换热的影响采用蔗糖水溶液形成分层层，从外圆柱（70 mm内径）开始加热，然后在两个圆柱间进行对流换热实验。在恒定的热通量下，从内筒（15 mm、30 mm或50.8mm O.D.）在恒定温度下。结果表明，内筒直径对对流换热的早期影响较大，当内筒直径增大时，对流换热表现出与竖直板间相似的换热特性。另一方面，当内筒直径较小时，平均换热系数随时间的推移接近稳态值，但不会超过稳态值.传热板间距对竖直板间自然对流传热的影响使用蔗糖水溶液形成分层层，并以恒定热流从一侧壁加热，以恒定温度从另一侧壁冷却。对传热板间距l= 10 mm、40 mm和60 mm的情况进行了实验研究，并与文献报道的l= 20 mm的实验结果进行了比较。结果表明，当蜂窝层厚度等于传热板间距时，平均传热系数变大.矩形槽内自然对流换热的数值分析本文对矩形槽内宽高比为0.1-20、Ra数为10^3-10^7的大范围内的自然对流换热进行了数值分析，并建立了换热系数的关联式，建立了稳定分层流体换热分析的理论模型。

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.