International Journal of Heat and Mass Transfer, Vol.55, No.23-24, 6307-6320, 2012
Interfacial heat transfer during microdroplet evaporation on a laser heated surface
A comprehensive experimental and numerical investigation on water microdroplet impingement and evaporation is presented from the standpoint of phase-change cooling technologies. The study investigates microdroplet impact and evaporation on a laser heated surface, outlining the experimental and numerical conditions necessary to quantify the interfacial thermal conductance (G) of liquid-metal interfaces during two-phase flow. To do this, continuum-level numerical simulations are conducted in parallel with experimental measurements facilitating high-speed photography and in-situ time-domain thermoreflectance (TDTR). During microdroplet evaporation on laser heated Al thin-films at room temperature, an effective interfacial thermal conductance of G(eff) = 6.4 +/- 0.4 MW/m(2) is measured with TDTR. This effective interfacial thermal conductance (G(eff)) is interpreted as the high-frequency (ac) interfacial heat transfer coefficient measured at the microdroplet/Al interface. Also on a laser heated surface, fractal-like condensation patterns form on the Al surface surrounding the evaporating microdroplet. This is due to the temperature gradient in the Al surface layer and cyclic vapor/air convection patterns outside the contact line. Laser heating, however, does not significantly increase the evaporation rate beyond that expected for microdroplet evaporation on isothermal Al thin-film surfaces. (C) 2012 Elsevier Ltd. All rights reserved.
Keywords:Two-phase;Evaporation;Condensation;Time-domain thermoreflectance;Simulation;Thermal conductance