Effect of the number of ribbed walls on the thermal performance in rectangular channels with 45-deg parallel or criss-cross ribs

Abstract

Regionally averaged heat transfer distributions and friction characteristics are experimentally investigated for fully developed, turbulent flow in a rectangular channel with a width-to-height aspect ratio (AR=3). 45-deg angled rib turbulators are placed on one, two, and four sides of the channel in parallel and criss-cross configurations with a pitch-to-height ratio(P/e=10) and a rib blockage ratio(eDh=4.1%). For a roughness Reynolds number range(e+=25−500), results show that increasing the number of ribbed walls improves the overall channel heat transfer for the 45-deg parallel ribs. Results reveal that four-sided ribbed channels provided the greatest thermal performance followed by the two-sided and one-sided ribbed channels, respectively, for both angled rib designs. On the basis of the law of wall similarity, friction and heat transfer roughness functions are derived using the four-sided data reported in this work. Furthmore, friction factors and heat transfer coefficients of similar angled rib designs were obtained from open literature and similarly correlated to derive more robust friction and heat transfer correlations over the roughness Reynolds number range. Thermal designers can use these proposed correlations to predict friction and heat transfer in rectangular cooling channels (AR=1-5) with various numbers of ribbed walls. The measured friction factor and heat transfer coefficient of this study can be predicted using these semi-empirical correlations with maximum errors of 9% and 7%, respectively.