Heat transfer enhancement to a confined impinging synthetic air jet

Heat transfer to confined, un-ducted and ducted impinging synthetic air jets is investigated experimentally. The influence of ducting on the cooling performance of synthetic air jets is of particular interest. Heat transfer to the jets is reported for a range of experimental parameters including jet exit to impingement surface spacings, H/D (from 0.5 to 3), ducting outlet diameter (1.2, 1.6 and 2 jet diameters) and length of the confining plate (90 to 200 mm). It is shown that increasing the length of the confining plate reduces the cooling performance by up to 14% in the stagnation region and 8% on an area averaged basis. Ducting is added to the jet to improve heat transfer by drawing cold air from a remote location into the jet flow. Across the range of parameters tested, ducting offers the largest increase in heat transfer at H/D = 1; at this spacing the 2 jet diameter ducting outperforms all others and can increase the heat transferred to the jet in the stagnation region by 27% and by 36% on an area average basis. At nozzle to impingement surface spacings greater 1 diameter ducting with a 1.6 jet diameters outlet offers the largest increase in heat transfer.