Measurement of phase distributions on the surface in subcooled pool boiling of FC-72

Experimental work using IR thermometry was undertaken to obtain phase distributions on the heated surface during subcooled pool boiling of FC-72 at atmospheric pressure. The time-averaged wetted area fraction (WF), the contact line length density (CLD), the frequency between dry-out events, the lifetime of the dry patches, and the dry patch size distributions on the surface were characterized through the observed data. The results confirmed that subcooling of the bulk liquid results in smaller bubbles and increased WF for a given superheat and thus higher critical heat flux (CHF). The subcooled boiling curve could be computed according to the heat flux through the liquid area weighted on WF, and CHF occurred when the WF decreased faster than the increase in heat transfer through the liquid area. CHF mechanisms that have been proposed in the literature were evaluated against the observations.