Flow and heat transfer characteristics of submerged impinging air-water jets

Flow and heat transfer characteristics of submerged impinging water jets were experimentally investigated. Air was mixed with water using a venturi tube installed before a pipe nozzle. The effects of the volumetric air fraction ( beta = 0.0-0.7) and jet impingement distance (L/D = 2-8) were studied at a water jet Reynold number, Rew, of 24,000. The air-water flow in the pipe nozzle and impinging air-water jet was recorded using a highspeed camera. An infrared thermal imaging camera measured local heat transfer on the impingement surface. Results show that heat transfer depends strongly on the volumetric air fraction. Impingement distance also affects the behavior of air bubbles in the water jet. Air bubbles can increase the heat transfer on the impingement region by increasing turbulence intensity in the jet with small air bubbles or an intermittent effect of large air bubbles impinging on the surface. Impinging jets where L/D = 4 with beta = 0.3 and L/D = 2 with beta = 0.2 give the highest heat transfer enhancement, about similar to 47% compared to the case of beta = 0.0.