带肋变截面回转通道内流动与换热的数值模拟

开发了三维流动换热的通用计算程序,数值研究了带肋变截面回转通道内流动与换热的特性.湍流模型采用低雷诺数k-ε模型.通道肋间距为25mm,肋高分别为1mm,1.5mm,2mm,冷气进口雷诺数Re分别为7500,12500,18500,25000.计算结果表明:①通道的平均努赛尔数均随进口雷诺数的增大而增大;②对于Re=7500和12500,肋高越高,换热越强;对于Re=18500和25000,肋高为1.5mm的通道换热最强;③局部雷诺数的不同和离心力的影响导致通道内各区域的局部换热随肋高的变化趋势并不一致;在进口段,肋高越高,换热越强;在出口段,当Re=7500和12500时,肋高越高,换热越强,而当Re=18500和25000时,存在最佳肋高1.5mm.

Numerical investigation of heat transfer and flow resistance in U-shaped variable cross-section channels with different rib heights

The flow and temperature distribution in U-shaped variable cross-section channels with different rib heights was investigated numerically by a new developed three-dimensional Navier-Stokes code with low Reynolds number k-ε turbulence model. The rib pitch is 25mm and the rib heights are 1mm,1.5mm,2mm respectively. The Reynolds number Re based on the inlet velocity of the cooling air and hydraulic diameter are 7500,12500,18500,25000. Numerical results reveal that the average Nusselt number of the channel increases with the increase of Reynolds number. The enhanced heat transfer was achieved with the higher rib height e when Re is equal to 7500 and 12500. The higher heat transfer characteristics can be reached for the case of e =1.5mm when Re is equal to 18500 and 25000. The effects of rib heights on local heat transfer show different behavior due to the different local Reynolds numbers and centrifugal force. The higher rib height e enhanced the heat transfer of inflow passage. In outflow passage, the higher the rib height, the better heat transfer behavior is produced for Re =7500 and 12500, while for Re =18500 and 25000 the optimum rib height is 1.5mm.