具有纵向外肋片的水平复合管外表面自然对流换热的数值计算

为了方便而有效地模拟具有纵向外肋片的水平复合管外表面大空间自然对流换热的数值计算时计算区域外边界条件,本文提出一种新的边界条件处理方式。数值实验表明,用该条件计算的具有恒壁温的水平圆柱外表面自然对流换热数值解与文献中的基准解相比,平均Nu数的误差在0.5％以下。本文在极坐标系下,采用固体区与流体区耦合计算原始变量法,模拟计算了具有纵向外肋片的水平复合管外表面在不同肋片高度和肋片数下的自然对流换热量。数值计算表明,管外布置6个对称的肋片时,在肋片相对高度h/r04.0时,对换热最为有利,对应的肋片管平均肋效率为87.92％;而在相同肋片高度下,布置8个对称的肋片时,换热量最大。

NUMERICAL COMPUTATION OF LAMINAR NATURAL CONVECTION HEAT TRANSFER AROUND A HORIZONTAL COMPOUND TUBE WITH EXTERNAL LONGITUDINAL FINS

A new boundary condition in the pseudo-boundary is developed to simulate numerically the laminar naturai convection heat transfer around a horizontal compound tube with external longitudinal fins. It can be implemented easily and more efficiently to save CPU time. Numerical tests indicate that the relative errors of the average Nusselt number of the laminar naturai convection around a horizontal isothermal cylinder using this boundary condition is less than 0.5% compared with the bench mark solutions available in the literature with less computational effort. The heat fluxes of the laminar naturai convection around a horizontal compound tube with different height of fins and different number of fins are calculated using the conjugated computation method with primitive variables in cylindrical coordinates. Numerical solutions show that for the tube with 6 fins the heat transfer rate reaches its maximum when the relative fins height h/r0 = 4.0, while for the tube with 8 fins the maximum heat transfer rate is obtained at h/ro = 3.64. Numerical results also revealed that the position of the fin has great effect on the heat transfer rate. For example, for the tube with 8 fins, the fin should not be positioned at the vertical line.