Heat transfer and horizontally averaged temperature of convection with large viscosity variations
Heat transfer and horizontally averaged temperature of convection with large viscosity variations
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粘度变化较大时的传热和对流水平平均温度
DOI：
10.1017/s0022112083000713
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发表时间：
1983
影响因子：
3.7
通讯作者：
S. Daly
中科院分区：
文献类型：
--
作者：
F. Richter;H. Nataf;S. Daly
使用粘度强烈依赖于温度的流体进行实验，用于研究 10−105 范围内的粘度变化对水平等温边界之间的对流层的传热和水平平均温度的影响。在较大的粘度变化（3 × 103 和 105）和瑞利数小于线性理论给出的临界值时，系统可以是传导性的或对流性的，具体取决于瑞利数是从早期的传导状态增加还是从预先存在的对流状态减少。在更高的瑞利数和所研究的整个粘度变化范围内，当瑞利数根据与等于边界温度平均值的温度相对应的粘度来定义时，传热与均匀粘度流体的传热差异很小（< 20%）。努塞尔数和超临界度 (Ra/Rc) 之间的关系更加显着，与粘度变化无关，并且与具有适当普朗特数的均匀粘度流体无法区分。由于冷、粘性较大的边界层上的温度变化相对较大，水平平均温度随着粘度变化的增加而变得越来越不对称，并导致等温内部温度明显高于边界温度的平均值。测量的温度和对流热传递作为深度的函数表明，对于大于约 100 的粘度变化，大部分粘度变化发生在系统活跃对流部分上方形成的停滞传导层内。
Experiments with fluids whose viscosity depends strongly on temperature are used to study the effect of viscosity variations in the range 10−105 on the heat transfer and horizontally averaged temperature of a convecting layer between horizontal isothermal boundaries. At large viscosity variations (3 × 103 and 105) and Rayleigh numbers less than the critical value given by linear theory, the system can be either conductive or convective depending on whether the Rayleigh number is increased from an earlier conductive state or decreased from a preexisting convective state. At higher Rayleigh numbers and for the entire range of viscosity variation studied the heat transfer differs little (< 20%) from that of a uniform-viscosity fluid when the Rayleigh number is defined in terms of the viscosity corresponding to a temperature equal to the average of the boundary temperatures. The relationship between Nusselt number and supercriticality (Ra/Rc) is even more remarkable being independent of viscosity variation and indistinguishable from that of a uniform-viscosity fluid with appropriate Prandtl number. The horizontally averaged temperature becomes increasingly asymmetrical with increasing viscosity variation due to the relatively large temperature change across the cold, more-viscous boundary layer, and results in an isothermal interior temperature significantly hotter than the average of the boundary temperatures. The measured temperature and convective heat transfer as a function of depth show that for viscosity variations greater than about 100 most of the viscosity change occurs within a stagnant conductive layer that develops above the actively convecting part of the system.