Blast Freezer Tunnel: Freezing Curve & Refrigeration Energy

Product

Tunnel Conditions

Air temperature −30 °C

Air velocity 4.0 m/s

Conveyor speed 1.00 m/min

Live Readouts

Exit-item core temp

— °C

entering

Refrigeration power

0.0 kW

System COP

—

Specific energy

— kWh/t

Throughput

— kg/h

Exiting fully frozen

—%

How it works

Each item cools by forced convection from the tunnel air. At every instant the heat flow out of an item of mass m is:

Q = h·(A/m)·m·(T − T_air)   [W]

Above the freezing point T_f, that heat leaves as sensible cooling — Q = m·cp_unfrozen·(−dT/dt). Once T reaches T_f, the temperature holds flat while the same Q instead removes latent heat of fusion: Q = m·L·(−d(frac frozen)/dt). Only once the whole item has frozen (frac = 1) does T resume falling, now at the slower rate set by cp_frozen < cp_unfrozen. That three-stage curve — precool, plateau, subcool — is exactly what a thermocouple buried in a real product shows in a blast tunnel.

The convective coefficient h rises with air velocity, h ∝ v^0.6 (turbulent forced-convection correlation), so a faster fan freezes product quicker but costs more fan power. Conveyor speed sets the residence time; if it's too fast for the chosen air conditions, items leave the tunnel still in the plateau or subcool stage — not fully frozen, flagged in the readouts.

The refrigeration system's coefficient of performance is modelled from evaporator/condenser temperatures against a fraction of the Carnot limit:

COP = η · T_evap / (T_cond − T_evap)      (η ≈ 0.45, T in kelvin)

Colder tunnel air means a lower evaporating temperature and a lower COP — freezing faster this way costs disproportionately more electrical energy per tonne. Electrical power draw is the sum of every in-tunnel item's heat load divided by COP, plus fan power (~v³). Specific energy (kWh per tonne) divides that power by the current mass throughput — the single number a plant actually gets billed on.

Simulation runs at accelerated (not real) time so a multi-minute freeze is visible in seconds — the underlying rate constants (h, cp, L) are unscaled.

Warm / precooling Freezing plateau Frozen / subcooling

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