This paper aims to examine the flow and heat transfer characteristics of impinging axial fan flows on a flat plate heated uniformly. The separation distance (the fan exit-to-flat plate distance H normalized by the fan diameter D) varies in a range of 0.2 ≤ H/D ≤ 2.0 while the axial fan is rotated with a fixed power input (12.0 DCV), leading to Reynolds number of Re = 9.0 × 103. The increased separation distance allows more surrounding fluids to entrain into the exit flow. As a result, the overall impinging heat transfer performance is decreased. For a given separation distance, the Nusselt number in the secondary stagnation region formed at the central part of the flat plate is lower than that in the outer flow region in which flow is spent to the surroundings, due to the presence of the neighboring wall jet interference in the secondary stagnation region.
Keywords: Axial flow fan; heat transfer; impingement; primary stagnation; secondary stagnation; separation distance