Numerical investigation of room temperature magnetic refrigerator using microchannel regenerators

The paper reports numerical investigation of room temperature, active magnetocaloric regeneration (AMR) refrigerators/heat pumps using microchannel regenerator. The microchannel regenerators are made of a magnetocaloric material (MCM), Gd, with diameter of the circular channels ranging from 0.7 mm to 2.0 mm. Water, the working fluid, oscillates in the regenerator loop driven by two piston-cylinder displacers operating in a range of mass flow rates. Three dimensional conjugated fluid convection and conduction heat transfer in the microchannel regenerator was modeled and numerically simulated using ANSYS Fluent. The magnetocaloric effect (MCE) was incorporated into conservation of energy using a discrete method to simulate the magnetization and demagnetization of the MCM. The hot and cold end heat exchangers were treated with the ϵ-NTU method. Effects of utilization and porosity of the microchannel regenerator and cycle frequency on the cooling capacity and temperature span were examined. When the utilization, porosity and cycle frequency are 0.2, 0.5 and 5.0 Hz, respectively, the predicted maximum cooling capacity was about 22 W for a 0.8 T variation in intensity of magnetic field. The effects of magnetic field intensity, reservoir temperature span and flow rate profile on the refrigeration performance were also investigated. The performance of the microchannel regenerator is compared with that of the parallel plate regenerator for the no-load temperature span, cooling capacity and pumping power. Under specific geometric and operating conditions, the microchannel regenerator shows better performance than the parallel-plate one.