Experimental Study And Numerical Simulation On Heat Transfer With Unsteady Impinging Jet

With high local heat transfer capacity, impinging jet heat transferaugmentation technology is regarded as one of the most popular cooling solutions forlocal high heat flux removal, so it has received great attention in both academic andengineering area. As the unsteady impinging jet can damage the boundary layer, so ithas a potential to increase heat transfer capacity compared with traditional steadyimpinging jet. In this paper, A preliminary experimental and numerical simulation forunsteady flow has been carried out in order to provide some fundamental insight forpractical application.Firstly, the whole experimental system is designed, which consists of thehardware part and software part. The hardware part includes gas pipeline system,flow rate measurement and control system, heating and temperature measurementsystem, apparatus frame and so on. The software part includes temperatureacquisition system, loss of thermal conductivity measurement system and signalgenerator control system and so on.Secondly, experimental study of the periodic impinging jet with differentparameters (waveform, frequency, height and Reynolds number) is carried out on thisexperimental platform to analyze the change rules of the waveforms and the effectsof various frequencies and impinging height on Nu. Research shows that therectangular waveform with step change tends to have better heat transferperformance and the down step change shows dominant function to augment heattransfer ability. Compared with steady flow, periodic jet does have a correspondingfrequency threshold to control the heat transfer effect which means the effect will beenhanced if the frequency is beyond the threshold value and vice versa.At last, numerical simulation of impact heat transfer phenomenon is done withsudden expansion nozzle jet and single nozzle jet with phase shift respectively. Forthe sudden expansion nozzle jet experiment, influence of parameters such as expansion ratio, height values and Reynolds number is analyzed. Research showsthat compared with inline nozzle, sudden expansion nozzle jet makes the averagecooling effect of the whole heat transfer plate become more uniform. And when theexpansion ratio is4or5, heat transfer effect is enhanced on the far side of the platealong the radial direction. Also to do simulation with single row nozzle jet withphase shift under different conditions, such as various sizes of phase, arrangement ofphase and frequencies to figure out the corresponding effects. Analysis obtainedshows that when the frequency is higher and the phase difference is120oarranged inorder, the heat transfer effect is best.