Effects of Pin-Fin Height on Flow and Heat Transfer in a Rectangular Duct

CFD simulations were performed to study the flow and heat transfer in a rectangular duct (W_d × H_d, where W_d/H_d = 3) with a staggered array of circular pin fins (D = H_d/4) mounted on the two opposite walls separated by H_d. For this array of pin fins, five different pin-fin height (H) combinations were examined, and they are (1) H = H_d = 4D (i.e., all pin fins extended from wall to wall), (2) H = 3D on both walls, (3) H = 2D on both walls, (4) H = 4D on one wall and H = 2D on the opposite wall, and (5) H = 3D on one wall and H = 2D on the opposite wall. The H values studied give H/D values of 2, 3, and 4 and C/D values of 2, 1, and 0, where C is the distance between the pin-fin tip and the opposite wall. For all cases, the duct wall and pin-fin surface temperatures were maintained at T_w = 313.15 K; the temperature and the speed of the air at the duct inlet were uniform at T_inlet = 343.15 K and U = 8.24 m/s; the pressure at the duct exit was fixed at P_b = 1 atm; and the Reynolds number based on the duct hydraulic diameter and duct inlet conditions was Re = 15,000. This CFD study is based on 3-D steady RANS, where the ensemble averaged continuity, compressible Navier-Stokes, and energy equations are closed by the thermally perfect equation of state and the two-equation realizable k-ε turbulence model with wall functions and with the low-Reynolds number model of Chen and Patel in the near-wall region. The usefulness of this CFD study was assessed by comparing predicted heat-transfer coefficient and friction factor with available experimental data. Results are presented to show how the flow induced by arrays of pin fins of different heights affects temperature distribution, surface heat transfer, and pressure loss.