Effects of gap size for parallel 45 degree angled rib turbulators

Abstract

Purpose – Turbulent air flows within a channel with 45° angled rib turbulators on the top and bottom walls are numerically predicted using the numerical code. For the predictions, a v2-f turbulence model (velocity variance scale and elliptic relaxation factor model) is utilized. The paper aims to discuss these issues. Design/methodology/approach – Three different rib arrangements with or without gap are investigated to present information on the effects of gap size on flow structure and heat transfer characteristics. Three-dimensional turbulent transport, and detailed flow structural characteristics are considered to provide new insight into the mechanisms which result in surface heat transfer augmentations. Findings – Compared to the baseline rib arrangement, the numerically predicted results show that the parallel ribs with gap (where the width of the gap is two times of rib height) shows the highest local Nusselt number ratios. This is a result of locally increased vorticity distributions, as well as augmented local magnitudes of mixing, secondary flows, and turbulent transport. Local transport changes are less pronounced when the gap width of gap is 0.5 times of rib height. As a result, associated local and spatially averaged Nusselt number ratios are also lower for this arrangement. Practical implications – Results will give improved heat transfer augmentation technologies. Originality/value – The present investigation provides new information and insight into flow structural characteristics in a channel with rib turbulators, both with and without gaps, especially the mechanisms which result in surface heat transfer augmentations, which are not available in any other existing numerical or experimental investigation.