Influence of the shape of the nozzle on local heat transfer distribution between smooth flat surface and impinging air jet

An experimental investigation is performed to study the effects of the shape of the nozzle, jet-to-plate spacing and Reynolds number on the local heat transfer distribution to normally impinging submerged air jet on smooth and flat surface. Three different nozzle cross-sections, viz. circular, square, and rectangular, each with an equivalent diameter of around 20 mm are used during this study. Reynolds number based on hydraulic diameter (d) is varied between 5000 and 15000 and jet-to-plate spacing from 0.5 to 12 nozzle diameters. Length-to-equivalent diameter ratio (l/de) of 50 is chosen for each nozzle configuration. The local heat transfer characteristics are estimated using thermal images obtained by infrared thermal imaging technique. Local and average Nusselt number on the impinged surface are presented for all the nozzle configurations investigated. Pressure drop measurements across nozzles are made and pressure loss coefficient for all nozzle configurations is reported. Average Nusselt numbers are found to be insensitive to the shape of the nozzle. (C) 2008 Elsevier Masson SAS. All rights reserved.