A novel magnetic cooling device for long distance heat transfer

Effective transfer of waste heat is a major challenge in a plethora of industrial and commercial systems and devices. Prolonged operation at elevated temperatures can adversely affect system performance, reliability, and service life. Conventional heat pipes are limited by their heat transport performance limitation at longer device length scales. On the other hand, we show that a magnetic cooling device, based on ferrofluid thermomagnetic convection, can transfer heat over much longer distance. We report the development and performance of an 8 m perimeter racetrack-shaped magnetic cooling device, an order of magnitude longer than conventional heat pipes. The temperature drop at the heat load was up to 41 °C for an initial heat load temperature of 197 °C. Cooling increased for larger heat flux, revealing the self-pumping and self-regulating nature of our device. The local Nusselt number exhibited a maximum near strong magnetic fields, resulting in enhanced cooling. The power transferred from heat load to the heat sink is maximum at higher heat load temperature, whereas the total power loss is minimum. The simulated velocity and temperature profiles revealed vortex formation and disruption of the thermal boundary layer, which also increased cooling. Heat load cooling by 17 °C was predicted even for a 20 m perimeter magnetic heat pipe. Our magnetic cooling device is a ferrofluid-based passive device for long-distance heat transfer, making it attractive for a wide variety of engineering applications.National Research Foundation (NRF)This research is supported by the National Research Foundation, Prime Minister's Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme

Optimal ferrofluids for magnetic cooling devices

Superior passive cooling technologies are urgently required to tackle device overheating, consequent performance degradation, and service life reduction. Magnetic cooling, governed by the thermomagnetic convection of a ferrofluid, is a promising emerging passive heat transfer technology to meet these challenges. Hence, we studied the performance metrics, non-dimensional parameters, and thermomagnetic cooling performance of various ferrite and metal-based ferrofluids. The magnetic pressure, friction factor, power transfer, and exergy loss were determined to predict the performance of such cooling devices. We also investigated the significance of the magnetic properties of the nanoparticles used in the ferrofluid on cooling performance. γ-Fe2O3, Fe3O4, and CoFe2O4 nanoparticles exhibited superior cooling performance among ferrite-based ferrofluids. FeCo nanoparticles had the best cooling performance for the case of metallic ferrofluids. The saturation magnetization of the magnetic nanoparticles is found to be a significant parameter to enhance heat transfer and heat load cooling. These results can be used to select the optimum magnetic nanoparticle-based ferrofluid for a specific magnetic cooling device application.National Research Foundation (NRF)Published versionThis research is supported by grants from the National Research Foundation, Prime Minister’s Office, Singapore, under its Campus of Research Excellence and Technological Enterprise (CREATE) program