Enhancement of impinging jet heat transfer on inner half-cylinder using two semicircular plates mounted near both sides of the convex curved exit

Abstract

We examined the flow-field characteristics of free jets issued from three types of jet exits opened on a convex curved surface for aspect ratios of 16, 12, and 9.6 and height h of 9, 12, and 15 mm, respectively. In addition, we examined the heat transfer characteristics of the impinging jet, the shear stress inside a half-cylinder, and the flow-field near the impinging jet region through flow visualization in cases where each jet impinges vertically onto the inner part of the half-cylinder. The impinging distance ratios H/h between the jet exit and its inside for height h were 4, 3, and 2.4; and two semicircular plates spaced at a value of W were installed parallel to both long sides of the exit. The Reynolds number of the jet based on the mean bulk velocity at the jet exit and height h was approximately 11,700, except in cases where the flow visualization was made using smoke, at which the Reynolds number was approximately 5800.The flow-field characteristics of the free jets were similar to those of a two-dimensional jet. The flow-field in the region surrounded by the inside of a half-cylinder and two semicircular plates can be classified into three flow patterns by changing the space, namely W/H. This revealed that the rate of increase in heat transfer coefficient became 20% larger than that of the jet operating power by controlling the flow-field using two semicircular plates; in this case, the impinging jet flow vibrated the surface at the center of the jet. It was also clarified that even when the local heat transfer coefficient changed when mounting semicircular plates, the time-averaged shear stress on the inside of the half-cylinder did not change within the impinging jet region.