Confined jet array impingement boiling

Confined jet array impingement boiling heat transfer is investigated for water at atmospheric pressure and inlet subcooling of 8°C for flow rates ranging between 0.33 and 0.67L/min. Three jet configurations consisting of 2×2, 3×3 and 5×5 arrays of 1.0mm diameter jets were tested for a jet-to-target spacing of 2mm. A 15mm×15mm plane copper surface was used as the heat transfer surface which formed a confined channel with the upper jet orifice plate. For a Reynolds number (Re) range of 900≤Re≤11,800, tests were performed by fixing the flow rate and progressively increasing the heat flux until the Critical Heat Flux (CHF) was reached. The results show that the single phase heat transfer coefficient increases with increasing Re and is reasonably predicted by a recent jet array heat transfer correlation. However, once fully developed boiling conditions are achieved, the heat transfer is generally insensitive to the flow rate and is predicted by the well-established Cooper pool boiling correlation. Consistent with earlier confined boiling studies, this suggests that the dominant heat transfer mechanisms are associated with the local bubble activity opposed to convective influences. Contrastingly, both the Onset of Nucleate Boiling (ONB) and CHF were found to be strongly dependent on the jet velocity. For the latter, it is related to the ability of the flow to clear the confined channel of vapour. CHF predictions are compared with the measurements showing good agreement.