Magnetocaloric Refrigeration Wheel

Magnet & Material

Applied field B_max 1.20 T

Material Curie point T_C 20 °C

Wheel speed 18 RPM

Cold-side heat load 0.10

Reservoirs

Hot side

20.0 °C

Cold side

20.0 °C

Span ΔT

0.0 °C

Revolutions

How it works

Near a ferromagnet's Curie temperature T_C, applying a field aligns the spins and drops the magnetic entropy S_M. Because the process is fast (adiabatic), total entropy must stay constant, so the lattice heats up. Removing the field lets the spins disorder again and the lattice cools — the magnetocaloric effect, modelled here with a Gaussian peak at T_C:

dT/dB ≈ ΔT_max · exp[-((T-T_C)/σ)²]
ΔT_ad ≈ -(T/C_p) · ΔS_M(T,B)

A rotary active magnetic regenerator (AMR) turns this into continuous refrigeration by cycling a wheel of material through a fixed magnet gap, four steps per half-turn:

Adiabatic magnetization — a segment enters the field, heats up (red).
Hot blow — while still in the field, it sheds that heat to the hot-side heat exchanger.
Adiabatic demagnetization — it leaves the field, cools below ambient (blue).
Cold blow — outside the field it absorbs heat from the cold-side reservoir, chilling it further.

Run over many revolutions the wheel pumps heat from cold to hot, exactly like a compressor-based fridge but with a solid magnetic material as the working substance instead of a gas. The Curie point slider shows why real machines use tuned Gd-Si-Ge or La-Fe-Si alloys: the effect is largest only within a narrow band around T_C. The heat load slider is a parasitic leak back into the cold reservoir — raise it and the cold side settles at a warmer steady state, just as a poorly insulated fridge box would.

Hot segment (in field) Cold segment (field off) Fixed magnet gap

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