Effects of additional transmission chamber on pulsed jet impingement heat transfer in a confined crossflow channel

Numerical simulations and schlieren imaging experiments are conducted in the present study to investigate the effects of an additional transmission chamber (ATC) on pulsed jet impingement heat transfer in a confined crossflow channel. A confined crossflow channel with H / D = 4 is considered, where the pulsed jet is examined at four pulsation frequencies ( f = 20 Hz, 50 Hz, 100 Hz and 200 Hz) and three jet-to-crossflow velocity ratios ( VR = 2.5, 5 and 10) with the jet Reynolds number fixed at Re j = 10,000. The results show that, within the range of parameters considered in the present study, the ATC mode is beneficial for pulsed jet impingement heat transfer at higher pulsation frequencies and higher jet-to-crossflow velocity ratios. The inherent flow inertia inside the ATC improves the ejection velocity of the pulsed jet during the off-duty stage of the pulsation cycle and subsequently increases the peak ejection velocity, especially at higher pulsation frequencies. Compared with the conventional long-pipe nozzle(LPN) mode, the critical threshold of Strouhal number under VR = 10 is slightly reduced in the ATC mode. Under VR = 2.5, although jet ejection during the off-duty stage still persists, the off-duty jet is strongly deflected immediately downstream of the exit because of the stronger crossflow effect, thereby losing its normal momentum toward the target stagnation zone. Therefore, the ATC mode has little influence on local Nu distribution in the situation of VR = 2.5, even at higher pulsation frequencies.