Natural convection of a heat-generating fluid confined in a frozen layer within a horizontal cylinder

当蓄热流体的水平圆筒的壁面被冷却到该流体的冰点以下时，内壁表面就会形成一层固体。同时，液体和固液界面之间的温度会在液体区域产生自然对流。例如，当熔盐增殖反应堆发生紧急关闭时，将在用作燃料盐储存容器的倾卸箱中观察到这种综合现象。在本项目中，进行了一项研究，以阐明这种组合现象的热特性。这项研究的大纲如下。采用有限差分法对水平圆柱体中生热流体在瑞利数≤10^8.2范围内的非定常自然对流进行了数值分析。采用高精度的马赫-曾德干涉仪测量了温度分布和传热系数。计算结果与数值结果非常吻合。在瑞利数7X10^<12>.4的范围内，通过实验得到了圆柱内努塞尔数和最高温度的估计方程。采用细差分法对水平圆筒内发热流体的凝固过程进行了数值研究。结果阐明了冻结层的特征和液体区诱导的自然对流。设计了一种近似计算冻结层厚度、最高温度、最大流函数和液体区平均努塞尔数的方法。

When the wall of a horizontal cylinder in which a heat-generating fluid is confined is chilled below the freezing point of the fluid, a solid layer is formedon the iner wall surface. Concomitantly, natural convection is induced in the liquid region by the temperature between the liquid and the solid-liquid interface. Such combined phenomenon, for example, will be observed in a dump-tank which is used as a storage vessel of fuel salt when an emergency shut dowm of a molten salt breeder reactor happens. In this project, a study was conducted to clarify the thermal characteristics of this combined phenomenon. The outline of this study was as follow.1. Unsteady natural convection of the heat-generating fluid in a horizontal cylinder was investigated through the numerical analysis by the finite difference method in the range of Rayleigh number up to 10^8.2. Temperature profiles and heat transfer coefficients were measured by Mach-Zehnder interferometer with a high accuracy. The results obtained were very much in agreement with the numerical results.3. Equations to estimate the Nusselt number and the maximum temperature in the cylinder were obtained experimentally in the range of Rayleigh number up to 7X10^<12>.4. A numerical study by finie difference method was carried out for the solidification of the heat-generating fluid in the horizontal cylinder. Results clarified th characteristics of the frozen layer and the natural convection induced in the liquid region.5. An approximate method was devised to estimate the thickness of the frozen layer, the maximum temperature, the maximum stream function and the mean Nusseltnumber in the liquid region.