GIFSQ Tools · Module 17 — Food Processing, Thermal Engineering & Utilities · Tool 327 of 500
Estimate the thawing time of a frozen food slab with a Plank-type equation, from thickness, freezing point, thawing medium temperature and heat transfer.
Try sample values — fills the form with the worked example below.
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Thawing time (h)
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Thawing time (min)
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Thawing rate (mm/h)
Equation: Plank-type equation (slab): t = (ρ × L / (Tm − Tf)) × (P × a / h + R × a² / k), with P = 1/2 and R = 1/8 for a slab, a = half-thickness in metres.
Method: Plank’s equation applied to thawing (Plank, 1913; Heldman and Singh, Food Process Engineering), with the thawing medium temperature in place of the freezing air temperature.
Assumptions: one-dimensional thawing of a slab heated from both sides; constant properties; sensible heat is not included.
Limitations: thawing is slower than the equation suggests because the thawed layer insulates the frozen core; thaw under refrigeration or in cold running water for food safety, never at warm room temperature for long periods.
Rounding: thawing time to 2 decimal places, thawing rate to 2; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Plank’s equation applied to thawing (Plank, 1913; Heldman and Singh, Food Process Engineering), with the thawing medium temperature in place of the freezing air temperature.
Assumptions: one-dimensional thawing of a slab heated from both sides; constant properties; sensible heat is not included.
Limitations: thawing is slower than the equation suggests because the thawed layer insulates the frozen core; thaw under refrigeration or in cold running water for food safety, never at warm room temperature for long periods.
Rounding: thawing time to 2 decimal places, thawing rate to 2; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: A 50 mm slab, freezing point −1 °C, medium at 20 °C, h = 30 W/m²·K, k = 1.5 W/m·K, density 1000 kg/m³, latent heat 250 kJ/kg: thawing time = 1.55 h (93.01 min).
Enter values above to see results.
Thawing in a refrigerator is slowest and safest; thawing in water or air is faster but the surface must not spend long in the danger zone. Tool 327 of 500 — GIFSQ
