冻结器传热的冷源相似准则

为解决冻结法模型试验中冻结管作为冷源的相似转换问题,将管内流动盐水和管壁的换热过程按对流边界条件处理,根据相似模拟理论推导出原型和模型之间的相似判据。理论分析结果表明:要满足冻结器原型与模型传热过程的相似性,模型中对流换热系数相似比与几何相似比的乘积应等于冻土的导热系数相似比。试验测试-30℃盐水(雷诺数为533~2 143)强迫对流换热的特征关联式系数。相似模型试验结果表明:当冻结管内盐水为层流状态时,在进行冻结法相似模型试验时除了要对盐水的温度进行设定外,还应按照冷源相似准则对模型冻结器中盐水的流量进行设定。如果盐水流量高于(或低于)该设定值,则模型的温度场将产生偏差。

SIMILARITY CRITERION OF FREEZING PIPE AS HEAT SINK DURING HEAT EXCHANGE

This article is aimed to solve the similar-transformation problem in using freezing pipes as the heat sink in the freezing model test. Considering the heat exchange between the flowing brine and the freezing pipe is the convection boundary condition，the similarity criterion between the prototype and the model is derived according to the theory of similar simulation. Theoretical analysis shows that the similarity of freezing pipe between prototype and model could be satisfied only if the product of geometric scale ratio and convection heat transfer coefficient scale ratio is equal to thermal conductivity scale ratio of frozen soil. Coefficients of forced convection heat transfer formula for brine at －30 ℃(Reynolds number in 533～2 143) was obtained in the experiment. The results of similar model test show that it is necessary to set brine flow rate of the freezer model in model experiment based on heat sink similarity criterion of freezing pipe in addition to setting brine temperature，especially under laminar condition. Some error would occur in model temperature field if the actual brine flow rate is larger or smaller than the setting value.