23 cm thick meat slabs having a thermal conductivity of k=0.47 W/m K and a thermal diffusivity of ɑ = 0.13 X 10-6 m2 /s is being frozen by refrigerated air at -30 oC . The meat slabs has a uniform initial temperature of 7 oC. The average convective heat transfer coefficient between the meat and the air is 20 W/m2 K. Assume that the size of the meat slab to be large relative to the thickness. a. Calculate the time required for the center of the meat slabs to drop to -18 oC [Second]. b. Calculate the surface temperature of the meat slabs at the time calculated in question a [oC]