A numerical simulation of the steady two-dimensional laminar natural convection heat transfer for the gaseous low-pressure flows in the annulus region between two concentric horizontal cylinders is carried out. This type of flow occurs in “evacuated” solar collectors and in the receivers of the solar parabolic trough collectors. A finite volume code is used to solve the coupled set of governing equations. Boussinesq approximation is utilized to model the buoyancy effect. A correlation for the thermal conductivity ratio (kr = keff/k) in terms of Knudsen number and the modified Rayleigh number is proposed for Prandtl number (Pr = 0.701). It is found that as Knudsen number increases then the thermal conductivity ratio decreases for a given Rayleigh number. Also, it is shown that the thermal conductivity ratio kr increases as Rayleigh number increases. It appears that there is no consistent trend for varying the dimensionless gap spacing between the inner and the outer cylinder () on the thermal conductivity ratio (kr) for the considered spacing range.
展开▼
机译:对两个同心水平圆柱体之间的环形区域中气态低压流的稳态二维层流自然对流换热进行了数值模拟。这种类型的流动发生在“抽空”的太阳能集热器和太阳能抛物线槽式集热器的接收器中。有限体积代码用于求解耦合的控制方程组。 Boussinesq逼近用于模拟浮力效果。对于普朗特数(Pr = 0.701),提出了以克努森数和修正的瑞利数表示的导热系数比(kr = keff / k)的相关性。发现随着克努森数的增加,对于给定的瑞利数,热导率降低。另外,示出了随着瑞利数的增加,导热率kr增加。似乎没有一致的趋势来改变内圆柱和外圆柱之间的无量纲间隙间隔( <移动器> L mi> g mi> msub> ? mo> mover> math>)所考虑的间距范围内的导热系数(kr)。
展开▼