Chapter 4, Problem 56P

Layers of 23-cm-thick meat slabs $(k=0.47\text{ W/m}\text{.K},\alpha \text{ = 0}\text{.13 }\times {\text{ 10}}^{\text{-6}}{\text{ m}}^{\text{2}}\text{/s)}$ and initially at a uniform temperature of 7°C are to be frozen by refrigerated air at -30°C flowing at a velocity of 1.4 m/s. The average heat transfer coefficient between the meat and the air is 20 W/m² K. Assuming the size of the meat slabs to be large relative to their thickness, determine how long it will take for the center temperature of the slabs to drop to -18°C. Also, determine the surface temperature of the meat slab at that time.