A contact plate freezer freezes a24 mm meat slab initially at its freezing point272.5 K. Water content85 wt%, water latent heat335 kJ/kg, plate temperature247.5 K, slab density750 kg/m³ and frozen conductivity1.5 W/(m K). Find minimum complete-freezing time in seconds.
For a slab frozen from both faces with negligible contact resistance, Plank’s minimum time is t=ρLf d²/(8kΔT). Effective latent heat per kg meat is0.85×335000 J/kg and ΔT=25 K. Thus t=750(0.85)(335000)(0.024)²/[8(1.5)(25)]=410.04 s, about410 s. Initial sensible cooling is absent because the meat starts at its freezing point.
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