Effect of Rib Shape on Flow Regime and Heat Transfer

Seyhun Durmuş

doi:10.34248/bsengineering.882373

Abstract

In current study, flow behavior and heat transfer properties in a square channel roughened with square, right triangle, isosceles triangle and circular ribs were examined. The validation test was performed for an experimental square rib case with a pitch ratio (P/e) of 9 and a blockage ratio (e/H) of 0.1. Only to examine the rib shape factor; height, base width, and rib spacing were taken the same in all cases. The study investigated the effect of various rib shapes on flow characteristics, overall thermal performances, normalized heat transfer distributions, and friction factors (pressure losses) at Reynolds numbers of 30,000 and 60,000. As a result of the numerical study, it was found that the rib shape effect did not cause as big differences in the flow properties as the blockage ratio (rib height) and pitch ratio (rib spacing) effect. In terms of the average Nusselt number enhancement, the right triangular ribbed case performed best, circular ribbed case performed worst, while the isosceles ribbed case performed better than square ribbed case. The isosceles ribbed case and right triangular ribbed case cause higher friction factor and pressure loss, while minimum friction is obtained in circular ribbed case and then in square ribbed case. As a result, in terms of overall thermal performances, right triangular ribbed case provided the best performance, followed by isosceles triangular ribbed case. The circular ribbed case produced less friction than the square ribbed case. The thermal performance of the square ribbed case was slightly higher than that of circular ribbed case.

Highlights

Turbulators are ribs in cooling channels that increase heat transfer by periodically interrupting the main flow and boundary layer
The results of the analysis showed that the velocity distributions did not change much for the different rib shapes
The flow pattern at recirculation and reattachment zones have shown similar properties for all cases where pitch to height ratio (P/e) was 9 and e/H was 0.1. This means that the rib shape factor is not as efficient to flow properties as the influence of the blockage ratio and pitch ratio

Summary

Introduction

Turbulators are ribs in cooling channels that increase heat transfer by periodically interrupting the main flow and boundary layer. There are many factors affect the aerothermal behavior of rib roughened ducts: Channel geometry (rectangular, square, trapezoidal, triangular), rib profile shape, blockage ratio, rib pitch, rib angle to the mainstream (30, 45, 60), rib configurations (staggered, transverse, V shape), 180° turn effect for multi-passed channels etc. As a result of these studies, it was concluded that ribs increase heat transfer but cause pressure drop due to surface friction and rib form drag effect (El Hadrami et al, 2002; Lee et al, 2003; Su et al, 2004). Rib pitch/ rib height ratios studied in the literature are typically in the 6-12 range (Keshmiri et al, 2002; Liu et al, 2006). The entrance length, entrance shape, refrigerant type, BSJ Eng Sci / Seyhun DURMUŞ

Methods

Results

Conclusion