Thermal performances of parallelogram channels with skewed ribs and tilted three dimensional fillets

Thermal performance improvements for ribbed channels are attempted by installing auxiliary fillets on ribbed endwalls. Detailed heat transfer distributions over two opposite endwalls enhanced by 45 degrees ribs and a row of tilted three-dimensional fillets of 1/2 rib heights with streamlined shape are measured at five flow configurations using steady-state infrared thermography method. Local, area-averaged and channel-averaged Nusselt numbers (Nu, (N) over baru and (N) over baru), Fanning friction factors (f) and thermal performance factors (TPF) for each test channel are examined with Reynolds number (Re) in the range of 5000-15,000. The HTE properties and associated f augmentations for the compound HTE measures are assessed by comparing the (N) over baru and f data detected from present test channels with the Nusselt numbers (Nu(infinity)) and f factors (f(infinity)) of smooth plain tube. Empirical correlations evaluating (N) over baru and f factors for present ribbed channels with/without in-lined/staggered fillets are generated. With present in-lined (staggered) fillets on two opposite ribbed endwalls, the HTE ratios in terms of (N) over baru/Nu(infinity) are raised to 4.43-4.21 (3.85-4.05) with forward flows and 4.31-4.02 (4.14-4.06) with backward flows at 5000 <= Re 15,000; whereas the corresponding f/f(infinity) ratios and TPF values fall in the respective ranges of 6.5-3.35 and 7.3-3.6 (7.5-5.6 and 9.06-7.39) with forward flows and 2.37-2.81 and 2.22-2.62 (1.97-2.29 and 1.99-2.09) with backward flows. As the (N) over baru/Nu(infinity), f/f(infinity) and TPF values for present ribbed channels with in-lined/staggered fillets are generally raised from the ribbed channel counterparts of 3.93-3.61 ((N) over baru/Nu(infinity)), 1.63-1.53 (f/f(infinity)) and 2.41-2.35 (TPF), the improved thermal performances by fitting the tilted fillets to enhance the rib-induced vortical flows are demonstrated. (C) 2016 Elsevier Ltd. All rights reserved.