Investigation of complex flow and heat transfer mechanism in multi-tube heat exchanger with different arrangement corrugated tube

Abstract

In this paper, the enhanced heat transfer performance and mechanism of a multi-tube heat exchanger (MTHX) with outward helically corrugated tubes (HCTs) are investigated by a numerical approach. Three types of tube arrangement (circle, square and triangle, indicated as CTA, STA and TSA, respectively) and four different tube spacings (1.25, 1.375, 1.5 and 1.625) are compared for Reynolds (Re) number ranging from 8900 to 89,400. Details of the coupled relationship among the multiple spiral detached vortices and turbulent pulsations are presented to explore the complex flow features. In addition, the variation trends of the average Nusselt number, friction factor, and performance index (PEC) are compared to obtain the optimum geometry parameter of the MTHX with HCTs. The results show that the rotational flow with opposite direction presents a strong overlay effect, and the circumferential velocity can reach up to 20% of the mean velocity. The non-directional turbulent pulsation only presents an overlap and strengthening effect. Besides, the secondary flow causes better heat transfer in the sub-layers, the turbulent pulsation has better heat transfer between the sub-layer and main flow region, while the rotational flow has a minor inhibiting effect on heat transfer performance. The TTA presents better interaction at the intervals of the tubes, and the Nu, f and PEC index of the TTA are all outstanding compared to the CTA and STA. The SL/Φt = 1.375–1.5 of the MTHX-TTA are suggested from the findings, and the Re should not exceed 40, 000.