Design analysis of a rotary-type magnetic cooler

Abstract

Heat flow across the disc of a rotary-type magnetic refrigerator was studied employing volumetric energy generation as a result of which the magnetocaloric material cools down. Gadolinium was selected as the magnetocaloric material due to its competitive cost and magnetocaloric effect. A 90° annular sector of gadolinium was implemented to the rotating disk and simulations were conducted based on the changing geometric values. Three different geometries of disk- magnetocaloric material assembly were studied where Ri = 5, 10, 15 mm, and Ro = 10, 15, 20 mm, respectively. Temperature behavior of the gadolinium was observed at varied disc geometries. Analysis was conducted for both the top surface and the midplane of the rotating disk, accounting for both convective and conductive heat transfer. A Nusselt-Rayleigh relation was obtained for the disks. The cycle was considered to have four processes which are magnetization process simulated by volumetric energy generation, adiabatic 90° rotation to cold side heat exchanger, surface heat flux to the magnetocaloric material within the heat exchanger, and 270° rotation accompanied by convective heat transfer back to the magnetic field, hence completing one cycle. It was observed that the gradient between steady-state temperature and the equilibrium (room) temperature decreases with decreasing gadolinium-to-disk area ratio. Conductive heat transfer through the thickness of the disk was not found to be significant compared to the convective heat transfer through the top surface.