点击次数：

论文类型：期刊论文

发表时间：2020-07-01

发表刊物：ENERGIES

收录刊物：SCIE

卷号：13

期号：13

关键字：supercritical CO2; convective heat transfer; vertical flow; gravity effect; numerical study

摘要：The effects of gravity on the heat transfer performance of supercritical CO(2)flowing within a vertical tube with a diameter of 4.75 mm are numerically studied in this paper. The main objectives are to comprehensively investigate the action of gravity and buoyancy on the supercritical heat transfer. An effective numerical method, which employs a modified Shear Stress Transferk-omega model (SSTk-omega), is applied at various gravity conditions. It is found that, for both upward and downward flows, the heat transfer of supercritical CO(2)is improved with increased gravity magnitude. The effect of gravity on heat transfer are more pronounced under a low mass flux condition than that under a high mass flux condition and it is closely related to the variations of thermal properties. For the upward flow, the increased gravity magnitude accelerates the near wall fluid and creates a classic "M-shaped" radial velocity distribution. For the downward flow, the increased gravity magnitude decelerates the near wall fluid and creates a parabola-like radial velocity distribution. On one hand, the turbulent kinetic energies of both the upward and downward flows are enhanced as the gravity magnitude increases, which benefits heat transfer dominated by turbulent eddy diffusion. On the other hand, high-density fluid with high thermal conductivity occupies the near wall region as the gravity magnitude increases, which benefits heat transfer dominated by molecular diffusion. The results might provide some instructive advice to improve the design and operation safety of heat exchanger at various gravity conditions.