Effects of jet plate size and plate spacing on the stagnation Nusselt number for a confined circular air jet impinging on a flat surface

Abstract

This work deals with the effects of jet plate size and plate spacing (jet height) on the heat transfer characteristics for a confined circular air jet vertically impinging on a flat plate. The jet after impingement was restricted to flow in two opposite directions. A constant surface heat flux of 1000 W/m 2 was arranged. Totally 88 experiments were performed. Jet orifices individually with diameter of 1.5, 3, 6 and 9 mm were adopted. Jet Reynolds number ( Re) was in the range 10,000–30,000 and plate spacing-to-jet diameter ratio ( H/ d) was in the range 1–6. Eleven jet plate width-to-jet diameter ratios ( W/ d = 4.17–41.7) and seven jet plate length-to-jet diameter ratios ( L/ d = 5.5–166.7) were individually considered. The measured data were correlated into a simple equation. It was found that the stagnation Nusselt number is proportional to the 0.638 power of the Re and inversely proportional to the 0.3 power of the H/ d. The stagnation Nusselt number was also found to be a function of exp[−0.044( W/ d) − 0.011( L/ d)]. Through comparisons among the present obtained data and documented results, it may infer that, for a jet impingement, the impingement-plate heating condition and flow arrangement of the jet after impingement are two important factors affecting the dependence of the stagnation Nusselt number on H/ d.