A food product is packaged in cuboid packs measuring 15 x 15 x 5 cm which enter a blast freezer at 10 deg C and leave when the center of the packs reach a temperature of -18 deg C. The air temperature is -30 deg C and the heat transfer coefficient is 150 W/sq. m K. Assuming the packs lie on one of the 15x15 faces, and that freezing takes place from other five faces, determine the freezing time using the following data: Freezing temp: -1.5 deg C; Frozen density: 900 Kg/cu.m Thermal conductivity: 1.0 W/m K; Specific heat (above freezing): 2,700 J/Kg K; Specific heat (below freezing): 1,500 J/Kg K Latent heat of fusion: 300 kJ/Kg.