Heat transfer enhancement between vertical wall and air in presence of expired or aspired jets : comparison between free and mixed convection conditions

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.This keynote lecture aims to determine the heat transfer enhancement in natural and in mixed convection between a vertical wall, heated by Joule effect, and air in the presence of small air pulsating aspirated and expired jets, in conditions of medium and large temperature differences between wall and air, namely from 25 to 70K. Experimental measurements have been taken both with and without pulsating and continuous expired and aspirated jets. The expired jets blow out perpendicularly from the wall surface. A thermo camera was used to ensure the wall temperature uniformity. A hot wire anemometer and visualization with smoke were used to found information about the air velocity field. The parameters which maximize the convective heat exchange have been computed. The present research represents a first step of a basic study to optimize the turbine behavior cooled by pulsating jets.