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Abstract This study experimentally investigated the effects of bubble coalescence on nucleate pool boiling. A micro heater array was used to generate vapor bubbles in FC-72 liquid with constant surface temperature boundary conditions while the heat flux at selected locations was measured using a high speed data acquisition system. The heat flux for boiling with coalescence was found to fluctuate much more than when only a single bubble formed on the surface due to the vaporization of the liquid layer trapped between the bubbles and oscillation of the bubbles after coalescence. These oscillations significantly increased the average heat transfer by increasing the frequency of rewetting of the heated surfaces compared to single bubble nucleation. The observations also showed that very fast coalescence events were not accompanied by an increase in the heat transfer rate as the liquid layer between the bubbles was physically pushed away by the rapid bubble growth during the inertial bubble growth stage instead of evaporating. The results show that the heat transfer increases for the dimensionless coalescence number, Ncoal, more than 0.2 but decreases for Ncoal less than 0.2.
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| Keywords
micro heater array
bubble dynamics
bubble coalescence
heat transfer
pool boiling
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Issue Date: 15 February 2014
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2014,
Vol. 54
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