Non-intrusive measurements of near-wall fluid flow and surface heat transfer in a serpentine passage

Flow visualization using a transient liquid crystal method is presented to study the effect of divider thickness on the local heat transfer distributi ons around a sharp 180-deg turn of a two-pass smooth square duct. Detailed local Nusselt number distributions on the bottom, blade-tip, and side walls are given for three divider thicknesses, W-d* = 0.10, 0.25, and 0.50, at a Reynolds number of 1.2 x 10(4). Complementary pressure loss measurements a re presented in terms of variation of friction factor with W-d*. The therma l performance investigation shows that W-d* = 0.25 provides the highest tot al averaged Nusselt number ratios, both at constant flow rate and at consta nt pumping power conditions, and a moderate friction factor. Near-wall lase r-Doppler velocimetry measurements are further performed to explain the liq uid crystal measured surface heat transfer distributions. The results show that the direction and strength of the secondary flow with respect to the w all are most important fluid dynamic factors affecting the heat transfer di stributions, followed by the convective mean velocity, and then the turbule nt kinetic energy. (C) 2000 Elsevier Science Ltd. All rights reserved.