A vertical slab of Wood's metal is joined to a substrate on one surface and is melted as it is uniformly irradiated by a laser source on the opposite surface. The metal is initially at its fusion temperature of Tf = 72°C, and the melt runs off by gravity as soon as it is formed. The absorptivity of the metal to the laser radiation is a1 = 0.4, and its latent heat of fusion is hsf = 33 kJ/kg.
(a) Neglecting heat transfer from the irradiated surface by convection or radiation exchange with the surroundings, determine the instantaneous rate of melting in kg/s · m2 if the laser irradiation is 5 kW/m2. How much material is removed if irradiation is main- tained for a period of 2 s?
(b) Allowing for convection to ambient air, with T00 = 20°C and h = 15 W/m2 · K, and radiation exchange with large surroundings (s = 0.4, Tsur = 20°C), determine the instantaneous rate of melting during irradiation.