Heat transfer enhancement by skewed wavy sidewall for two-pass ribbed channels with different aspect ratios

Abstract

Thermal performances of the newly devised compound heat transfer enhancement (HTE) method by deploying the in-line 45° ribs and skewed waves along the two opposite pairs of channel endwalls and sidewalls, respectively, for three two-pass sharp-bend channels with aspect ratios (AR) of 0.5, 1 and 2 are studied. For each test channel at Reynolds number (Re) between 5000 and 20,000, the full-field Nusselt number (Nu) distributions over the ribbed endwall and the channel-averaged pressure drop coefficients (f) are measured to determine the thermal performance factors (TPF) as the efficiency indices for heat transmissions. A set of Nu, f and TPF data obtained from the three test channels is selected to illustrate the HTE properties and the associated f augmentations. With present orientations for the skewed sidewall waves and the 45° endwall ribs to trip the co-current axial swirls, the local and area-averaged endwall Nusselt numbers (Nu‾A) are considerably raised by elevating the HTE benefits over the mid-rib regions. The Nu‾A levels over the ribbed endwalls for present test channels with AR=0.5, 1 and 2 are respectively raised to 4.74–3.83, 6.25–4.94 and 7.43–6.09 times of the Dittus–Boelter references. With the accompanying f augmentations to 24.54–12.44, 17.35–10.42 and 26.71–19.82 times of the Blassius levels, the TPF values for present test channels of AR=0.5, 1 and 2 fall in the ranges of 1.74–1.62, 2.42–2.24 and 2.51–2.28 respectively. The averaged Nusselt number correlations over inlet/outlet legs, turning region and entire endwall, as well as the f correlations, for present test channels are generated to assist the design activities.