超临界压力下水在螺旋管内的混合对流换热

Mixed Convective Flow and Heat Transfer of Water in a Helicoidal Pipe under Supercritical Pressure

采用FLUENT 6.0 CFD商业软件,对螺旋管内超临界压力下水在发展段的层流混合对流换热特性进行了数值研究,细致地分析了螺旋管螺距、入口流动Grashof数和Dean数等对流动和换热的影响.研究结果表明,在超临界压力下,水物性参数的剧烈变化在垂直流动方向引起了很强的二次流动,同时由螺旋管引起的向心力也造成了很强的二次流.与相同尺寸直管道相比,螺旋管内二次流的存在大大强化了流动换热,但是也相应地增加了流动阻力,因此螺旋管入口De数越小,则二次流越大,摩擦阻力越小.同时,流动换热随质量流速的增加而增加.

To reveal the features of mixed convective flow and heat transfer in supercritical fluids, a numerical investigation was conducted for the developing laminar heat transfer of water in a smooth helicoidal tube with the CFD software FLUENT 6.0. The effects of dimensionless pitch, inlet Dean number, and inlet Grashof number on the mixed convective flow and heat transfer was analyzed. The results show that under supercritical pressure, the sharp change of thermophysical properties of water and the centripetal force in helicoidal tube obviously induce secondary flow pattern in radial direction. Compared with straight pipe of the same size, the existence of secondary flow in helicoidal tube enhances the convective heat transfer remarkably, but significantly increases the friction factor. With decreasing of De number in the inlet of the helicoidal tube, the secondary flow is strengthened, and the friction factor is weakened. In addition, the convective heat transfer is enhanced as the mass flow rate increases.