We have presented results from a numerical study of two very different models for active magnetic refrigeration. Firstly a conventional fluid model utilizing 50µm plates of a perfectly graded Gd-like material. This model had enhanced heat transfer between MCM and fluid by means of a "Dream pipe" effect. This effect was implemented by a multiplied factor to the Nusselt number. Maximum cooling power for this model is 10kW/l. Secondly a conceptual model was evaluated. The model uses thermal switches to control the heat flow in the MCM thus dispensing with the heat transfer fluid. In this model the thermal conductivity of the MCM was increased between 10 and 400 J/kg/K. The maximum cooling power for this model is 34kW/l. The intention of the study has been an open minded exploration of parameters. A number of challenges exist in the realization of a device utilizing thermal switches: Magnetizing very thin segments; Obtaining a sufficient high ratio of heat conduction in the ON and OFF state of the thermal switches; Obtaining adequate thermal transfer in the MCM. Unlike in the fluid model heat transfer through the MCM is desirable and necessary. The novel method of controlling the heat flow direction has a distinct effect on the COP. The disposal of heat transfer fluid removes many loss terms. If thermal switches can be produced with a high dynamic range of heat conduction, this model has very high applicable potential. The "Dream pipe" increase in thermal transfer from a solid MCM to a heat transfer fluid will likely have a corresponding increase in pressure drop. However with no additional improvements and without a prohibitive pressure drop the accurate production of 50µm MCM plates will give a high volumetric cooling power even with 60 K temperature span.
Modeling of In-vehicle Magnetic refrigeration
2012
8 Seiten, 8 Bilder, 1 Tabelle, 14 Quellen
Conference paper
Storage medium
English
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