Influence of pulse shape of single pulsed air jet impingement system on heat transfer

Pulsed air jet impingement system is one of the most important area of heat transfer studies due to its wide engineering applications in heating and cooling such as in textile drying and electronics cooling. In this paper, the tests parameters used are a constant Reynolds number of 16000, Copper impingement plate surface temperature of 100°C, radial distance to nozzle outlet diameter ratio (r/d) in the range of 0 and 6 and different pulse frequencies of 0 Hz and 60 Hz. Duty cycles of 0.18, 0.27, 0.31 and 0.35, the cylindrical pulse mechanism shape with four different circular areas of 314.16, 514.16, 614.16, and 714.16 mm
²
and two different nozzle diameters of 15 and 20 mm diameter are used. The objectives of this paper are to determine the effect of pulse shape and the nozzle diameter towards the heat transfer enhancement. Results obtained show that for nozzle with diameter of 20 mm (pulse shape 4), the maximum heat transfer rate is recorded at plate distance to nozzle outlet ratio (z/d) equals to 4 and for 15 mm nozzle diameter (pulse shape 1), the maximum heat transfer rate is recorded at z/d equals to 2. Optimum frequency is between 30 Hz and 50 Hz while highest heat transfer enhancement is between z/d of 2 and 4.