Boiling heat transfer characteristics of pin-finned surface in distributed jet array impingement

In order to explore the effects of different jet positions in distributed jet array impingement boiling, a visualization study on pin-fin surfaces is conducted with HFE-7100 as the liquid coolant. The effects of three jet positions (Position I, II and III are the relative position for jet orifices locating in the middle of two pin-fins, on the top surface of pin-fins and in the middle of four pin-fins, respectively.) with different subcooling degrees, flow rates and jet distances on heat transfer characteristics of jet boiling are studied. Meanwhile, the effects of jet positions on bubble dynamics and pressure drop of jet impingement boiling are investigated with emphasis. For each jet position, increasing the subcooling all decreases the onset of nucleate boiling (ONB). Moreover, because of the dominant role of nucleate boiling, the flow rate has little effect on heat transfer coefficient in fully-developed nucleate boiling regimes. The effects of jet distances on heat transfer are different for three jet positions, but there should be an optimum jet distance to achieve the best heat transfer performance. It is found that there are basically no differences in the cooling performance of the three jet positions in single-phase heat transfer regime, while different jet positions principally affect the boiling heat transfer. Meanwhile, different jet positions have similar heat transfer behaviors in the fully boiling regime. Different heat transfer characteristics of jet boiling for three jet positions are induced by different velocity distribution around pin fins and bubbles exhausted effectively or not.