HEAT TRANSFER ENHANCEMENT BETWEEN A VERTICAL WALL AND AIR WITH PULSATING ASPIRATED AND EXPIRED JETS

This paper aims to determine the enhancement of heat transfer in natural convection between a vertical wall, heated by Joule effect, and air in the presence of small air pulsating aspirated and expired jets. Experimental measurements have been taken both with and without pulsating and continuous expired and aspirated jets. The jets blow out perpendicularly from the wall surface. The thickness of the boundary layer near the wall is locally reduced because of the presence of the aspirated jets or the boundary layer is destabilized near the holes by means of expired jets: in both ways the heat transfer coefficient is improved. Contact thermocouples are connected to a Keithley multimeter. All the data are acquired by means of a personal computer. The temperature uniformity is obtained by the regulators that supply electrical power to the thermo-resistances. This uniformity is assured by means of an AVIO Neo Thermo TVS-600 infrared video camera. A hot wire anemometer was used to found information about the air velocity field. The experimental results have demonstrated that the pulsating expired jets are more efficient than the aspirated ones with lower temperature difference between wall and air, the opposite occurs when the difference is greater then 40K. We have also computed the intervals of presence and absence which maximize the convective heat transfer coefficient.