Flow and heat transfer characteristics of micro pin-fins under jet impingement arrays

Abstract

Within the present investigation, the combination of impingement jet arrays and arrays of target surface micro pin-fins is investigated. The use of arrays of micro pin fins for installation in different application environments is made possible by recent developments in additive manufacturing. Considered are effects of impingement jet Reynolds number (with values from 2000 to 20,000), jet-to-target plate distance (with Z/D values of 0.75 and 3.0), micro pin-fin shape (rectangle and pentahedron), and micro rectangle pin-fin height (with h values of 0.05D, 0.2D, and 0.4D). Presented are variations of discharge coefficient, area-averaged Nusselt number, and area-averaged Nusselt number ratio. Area-averaged Nusselt number variations for the different data sets are a result of the effects of increased wetted surface area, turbulent transport and turbulent mixing, thermal conduction resistance from pin-fin material, and local flow separations and recirculation regions. When compared at a particular streamwise location, Z/D, and Re value, area-averaged Nusselt number ratios generally increase with height for the rectangle micro pin-fins. When Z/D = 3.0, Nusselt number ratios show heat transfer augmentations of 30–130 percent, which are approximately constant as streamwise row location changes, provided comparisons are made for constant Re, Z/D, and h/D. Different behavior is present Z/D = 0.75, since associated Nusselt number ratios vary significantly with streamwise row location, with augmentations which range from 0 to 160 percent, because of the influences of narrow jet-to-target plate distance and impingement passage flow confinement.