Effect of Orifice Shape on Flow Behavior and Impingement Heat Transfer

Impingement jets are widely used in industries because they provide a high heat transfer coefficient near the stagnation region. However, few methods exist for controlling impingement heat transfer. Recently, a peculiar diffusion process called "axis switching" for three-dimensional free jet has begun to attract attention, and there is a novel possibility of control diffusion and mixture process using this phenomenon. In this paper, we report on the effect of non-circular polygonal orifice shapes on impingement heat transfer. In addition, we demonstrate axis-switching phenomenon by using flow visualization with hydrogen bubbles. Orifice configurations are the regular polygons with 3 to 6 sides. Heat transfer experiments covered the distance between the orifice-to-target plate is 4 to 8 and Reynolds number is 5 × 10 4 and the heat flux is 600 W/m 2 . The flow was visualized in Reynolds number 1,500. For a free jet emerging from a regular polygonal orifice, the location of axis-switching phenomenon shifts toward the orifice exit as the number of sides on the orifice is increased. The iso-Nusselt number profile tends to take the shape of a concentric circle farther upstream. However, with a decrease in the number of sides of the orifice, the iso-Nusselt number profile after axis switching remains downstream. ing the flow using hydrogen bubbles. We also investigated the heat transfer characteristics of an impinging air jet from a non-circular orifice shapes including triangle, square, penta- gon, and hexagon. Moreover, we examined the possibility of controlling impinging heat transfer by changing the orifice configuration.