Abstract
Experiments are conducted to investigate turbulence enhancing effects of a porous mesh-screen with a sinusoidal shape normal to the flow direction inside a rectangular cross section air channel at low Reynolds numbers (i.e., Re = 1360-3800). The baseline measurements are obtained at the same channel and Reynolds numbers without the screen present. The surface of the screen pores are oriented parallel to the mean flow. Data are presented for the total and wall-static pressure drop along the channel, Nusselt number distributions on the heated wall at several constant heat rates, and air temperature distributions at the channel exit with and without (baseline cases) the screen. The heat transfer measurements are obtained with one wall heated as well as two parallel walls heated to simulate different applications for air channels in the flat plate heat exchangers. The results indicate that the ratio of screen channel to baseline Nusselt number (Nu/Nu(0)) and the ratio of screen channel to baseline friction factor (f/f(0)) increase with the Reynolds number (Re). The fully developed Nu/Nu(0) is 2.0-2.5 as the fully developed f/(f)0 is 4.4 at 3100 < Re <= 3800. However, the screen channel heat convection performance index, (Nu/Nu(0))/(f/f(0))(1/3) is only greater than 1.0 when Re > 2500 which is the design objective of reducing the pumping power and heat transfer area in the channel. Nonetheless, the screen insert is only beneficial to augment the convective heat transfer in the channel over the range of transition Reynolds number tested. The average total pressure drop across the channel and average exit air temperature suggest that the screen insert promotes good mixing of fluid across the channel for the Reynolds numbers tested.