Nuntadusit C.
Flow and heat transfer characteristics of impinging jet from pipe nozzle with vortex generators
The objective of this study is to investigate the heat transfer characteristics of impinging jet from pipe nozzle with vortex generators at nozzle exit. The half delta-wing vortex generators were applied into inner pipe with two arrangements of 2 vortex generators placed 180o apart and 4 vortex generators placed 90o apart. The effect of attacking angles were also studied at θ=45o and 60o. All experiments were performed at constant jet Reynolds number at Re=29,500 for comparison. The jet-to-plate distances were varied at H= 1D, 2D, 4D, 6D and 8D (D is the inner diameter of pipe nozzle). The heat transfer characteristics were investigated using Thermochromic liquid crystal sheet and the image processing technique was used for evaluating the distribution of wall temperature and Nusselt number. The flow pattern of free jet flow was also visualized in water tunnel with laser fluorescent dye technique. For case of 2 vortex generators, the heat transfer pattern divides in two peaks in jet impingement region when jet-to-plate distance H is larger than 4D and the distance between these two peaks increases with increasing the jet-to-plate distance. For case of 4 vortex generators, the heat transfer patterns looks like cross mark symbol at small jet-to-plate distance and become same with the conventional case at large jet-to-plate distance H=6D and 8D. The cases of 2 and 4 delta-wings with θ=60o can be used for heat transfer enhancement in impingement region.
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