Thermal switching requirements for solid state magnetic refrigeration

Abstract

Magnetic refrigeration, based on the magnetocaloric effect, is an attractive alternative to the conventional vapor-compression technology. In a solid state magnetic refrigerator the traditional alternated fluid flow is replaced by two solid thermal switches (TSs) that control the heat flux. These TSs are materials, or devices, whose thermal conductivity changes with an external stimulus. Here, we numerically investigate how the performance of a solid state magnetic refrigerator depends on the TS thermal conductivities (k) and corresponding k-variations (Δk) with the magnetic field. Two different scenarios were considered: a single TS and a double TS magnetic refrigerator. We have numerically varied the thermal conductivity of the thermal switches, operating frequency and working temperature. The use of only one thermal switch with near-ideal Δk is enough if the required performance does not overcome half of the adiabatic temperature change (ΔTad) of the magnetocaloric material. To overcome this value the device must use two effective thermal switches. Using an additional thermal switch is only beneficial when ΔTad needs to be overcome, or when the first thermal switch shows a modest Δk. These results simplify the operability control, which will increase the interest for magnetically activated thermal switches operating at acceptable magnetic fields.