Effect of the profile of a convergent nozzle on heat transfer distribution of a flat plate impinged by an under-expanded jet

An experimental investigation is performed to study the effect of the profile of a convergent nozzle on the local heat transfer distribution of a smooth flat surface impinged normally by an under-expanded air jet. Two convergent nozzles of different expansion profiles having same throat diameter of 5.6 mm are employed. Measurements are carried out for nozzle pressure ratios (P-0/P-infinity) of 2.36, 3.04, 3.72, 4.4 and 5.08 at different nozzle-to-plate distances (z/d= 1, 2, 3, 4, 6, 8, 10, 12 and 15). Flat surface made of thin stainless steel metal foil acts as a heated target plate. Local temperature distribution is measured using thermal infrared camera and the surface pressure distribution is measured on an impingement plate. Local Nusselt numbers and the adiabatic wall temperatures are obtained using linear regression method. The recovery factor distributions for various nozzle-to-plate distances are presented. Nusselt number and the recovery factor distributions are significantly affected by the profile of the convergent nozzle particularly at lower nozzle-to-plate distances in the stagnation point region and not in the wall jet region. (C) 2012 Elsevier Inc. All rights reserved.