Area of bubble influence due to sliding bubbles in subcooled boiling flow

The heat transfer effect of sliding bubbles is discussed in two aspects based on new experimental findings: (i) the area of bubble influence and (ii) bubble sliding characteristics influencing the degree of wall heat transfer. One notable finding was that the bubble sliding behavior, characterized by sliding trajectories, played a crucial role in determining the area of bubble influence and the bubble influence factor (K). Also, such sliding characteristic was observed strongly dependent on the sliding bubble size. An empirical model has been proposed based on this finding to evaluate the bubble influence factor (K) for the sliding bubbles. Another experimental finding was that the bubble sliding characteristic, represented by bubble spreading factor (S), had a significant impact on the degree of wall heat transfer induced by sliding bubbles. This is due to the fact that the bubbles spread across the heater width as they slid downstream, which reduced the effective frequency of sliding bubbles per unit wall area. These new findings not only improve our understanding of the heat transfer associated with sliding bubbles, but also are expected to contribute to improving the insight in the existing CFD boiling heat transfer models. (C) 2018 Elsevier Ltd. All rights reserved.