Mesoscale simulation of heater size and subcooling effects on pool boiling under controlled wall heat flux conditions

Effects of heater size and subcooling on pool boiling from horizontal heated hydrophilic and hydrophobic surfaces under controlled wall heat flux conditions are numerically simulated with a new scheme of phase change lattice Boltzmann method. Simulation results confirm that the shape of saturated pool boiling curves depends greatly on the ratio of heater length (L-H) to the capillary length (l(0)). For large heaters with L-H/l(0) >= 12, boiling curves collapse into one and the heater can be considered to be of infinite size. For heater sizes in the range of 4 < L-H/l(0) < 12, the heater size has great influence on CHF, transition boiling and film boiling regimes. It was found that the CHF increases with the decreasing heater size and existing correlation equations on heater size effects on critical heat flux are valid. For small heaters with L-H/l(0) <= 4, the transition boiling regime disappears, and the nucleate boiling mode switches to the film boiling mode immediately as the wall heat flux is increased. It is also shown that subcooling has relatively small effects in natural convection, in the nucleate boiling regime and film boiling regime, but it enhances CHF greatly and shorten the transition boiling regime. The relationship between simulated critical heat fluxes of saturated and subcooled nucleate boiling in pool boiling agrees well with existing correlation equations. (C) 2016 Elsevier Ltd. All rights reserved.