Abstract

The present work numerically studied the enhanced heat transfer mechanism of the coupled fields of detached and spiral vortices in symmetrical and asymmetrical spirally corrugated tubes. The heat transfer and viscous dissipation were analyzed by evaluating the entropy combined with the flow patterns, and the global entropy generation rate was analyzed by considering the local Nusselt number and friction factor. The results indicated that, both the leeside and windward corrugation angles had obvious effects on the strength of detached vortex and spiral flow, and also the location of the vortex. The maximum values of the heat transfer entropy were located at the boundary layers, and the heat transfer entropy of the secondary flow region was more distinguished than in other parts of the main flow region. The maximum values of friction entropy generation were located at both the boundary layers and the core of detached vortex. The performance evaluation criterion (PEC) presents nearly the same values for the four cases, when the Reynolds number (Re) is less than 6,300. In addition, the PEC of symmetrical spirally corrugated tube with corrugation angle equal to 25° showed the best performance, when Re is greater than 6,300. To keep the PEC above 1, Re should not exceed 33,000.

摘要

目前的工作数值研究了对称和非对称螺旋波纹管中分离和螺旋涡耦合场的增强传热机制。通过结合流动模式评估熵来分析传热和粘性耗散，并通过考虑局部努塞尔数和摩擦因子来分析全局熵产生率。结果表明，背风波纹角和迎风波纹角对分离涡和螺旋流的强度以及涡的位置都有明显的影响。传热熵的最大值位于边界层，次流区的传热熵比主流区的其他部分更显着。摩擦熵产生的最大值位于分离涡的边界层和核心处。当雷诺数 (Re) 小于 6,300 时，性能评估标准 (PEC) 为四种情况呈现几乎相同的值。此外，当Re大于6300时，波纹角等于25°的对称螺旋波纹管的PEC表现最佳。为了使 PEC 保持在 1 以上，Re 不应超过 33,000。