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Thermodynamics and engines (A-level only)

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Question 10

A portable cryo-therapy sleeve is used by sports physiotherapists to apply rapid localized cooling to athletes' injured joints. Under typical operating conditions, the temperature of the cooling plate (cold side) is maintained at 5 ∘C5\ ^\circ\text{C}5 ∘C while the temperature of the heat-dissipating fins (hot side) is at 55 ∘C55\ ^\circ\text{C}55 ∘C.

Manufacturer data for this cooling unit show that:

  • the rate at which heat is rejected from the hot side is 150 W150\text{ W}150 W
  • the electrical power supplied to the device is 75 W75\text{ W}75 W
1.

It is claimed that the coefficient of performance (COP) of a thermoelectric cooler is much less than the COP of an ideal (reversible) refrigerator operating between the same temperatures.

Discuss whether this claim is valid for the cryo-therapy sleeve under these conditions.

[4]
2.

Suggest why a relatively low value of the COP is acceptable for this portable athletic therapy application.

[2]

Thermodynamics and engines (A-level only) Questions

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