EXPERIMENTAL AND CFD ANALYSIS OF SWIRL, NOZZLE ARRANGEMENT, CROSS-ECTION AND JETS DIAMETER ON HEAT TRANSFER IN MULTI-JET AIR IMPINGEMENT COOLING

Experimental investigation and CFD analysis were performed to study the effects of swirl, nozzle arrangement, cross section of nozzle, number of jets and jet diameter on heat transfer coefficient in multi jet air impingement cooling fora target surface of 100 x150 mm size supplied with a constant heat flux of 7666 W/m'. The normalized heat transfer coefficient based on unit volume of air is evaluated through measurement of temperature for flow Reynolds numbersin the range of 8000-22000 with H/D ratiosof 1, 2, 4, and 6. Investigations with and without swirl reveal that among the tested conditions, for 8 mm jets, introducing swirl reduces the heat transfer where as for 10 mm and 12 mm jets, swirl improves the average heat transfer rate. For sets of 12 nozzles configurations, the staggered arrangement for 6 mm and 8 mm nozzles results in higher heat transfer rate than in-line arrangement unlike in 4 mm nozzles where in-line arrangement is better. Heat transfer coefficients for circular, square and triangular cross-sections of sameflow area have been compared. Circular cross-section offers better heat transfer coefficient for all the tested conditions. For a given number ofnozzles, there is an optimum diameter corresponding to maximum value of normalized heat transfer coefficient. The results are corroborated with CFD analysis for afew representative conditions tested.