Preservation of Food

A contact plate freezer extracts heat from a 24 mm thick slab of boneless meat (85% w/w water). Initial slab temperature = freezing point = 272.5 K; latent heat of freezing = 335 kJ/kg water. Plate temperature = 247.5 K (steady). Bulk density = 750 kg/m³; thermal conductivity of frozen meat = 1.5 W/m·K. Find the minimum duration for complete freezing (s).