Effect of pin inclination angle on flow and heat transfer characteristics for a row of pins in a flow channel

摘要

The aim of this research was to study flow and heat transfer characteristics with a row of inclined pins in a rectangular channel. The cylindrical pins of diameter D = 10 mm were mounted on the heat transfer surface in spanwise direction of the channel. The pin-to-pin distance was fixed at S = 2D. Two of pin heights H were studied, namely short pins or long pins with H = 2D or H = 3.2D, respectively. The effects of pin inclination angle were investigated for θ = 30°, 45°, 60°, 90°, 120°, 135°, and 150° in the range of Reynolds number from 14,000 to 32,860. The local temperature on endwall surface was measured using a thermochromic liquid crystal sheet coupled with image processing. Numerical simulations were used to obtain three-dimensional flow fields and heat transfer rates on pin surfaces and endwall surface. Results for the case H/D = 2 show that pins inclined by θ = 30°, 45° and 60° can enhance heat transfer downstream of the pin row, from the baseline case of pins with θ = 90°. The heat transfer was improved by a pair of counter-rotating vortices near the heat transfer surface. These vortices induced the main flow to attach on the heat transfer surface. The pin inclinations θ = 120° and 135° somewhat improved heat transfer behind the pins. However, the inclination θ= 150° gave the lowest heat transfer rate on the endwall surface. The heat transfer on endwall surface with H/D = 3.2 was poorer than with H/D — 2 because the counter-rotating vortices did not reach the heat transfer surface. The inclination θ = 30° with H/D = 2 gave the best thermal performance. The local Nusselt number on the rear side of pin surfaces with H/D = 3.2 and inclinations θ = 30°, 120°, 135° and 150° tended to increase from the case H/D = 2, due to a jetlike flow attachment on the pin surfaces. However, the local Nusselt number on pin surfaces with H/D = 3.2 and inclinations θ = 45° and 60° tended to be lesser than with H/D = 2, due flow separation downstream far from the pins.