Experimental investigation and performance comparison of Fe3O4/water and CoFe2O4/ water ferrofluids in presence of a magnetic field in a cooling system

Background: Cooling has a great effect on improving equipment performance. One of the effective ways to increase heat transfer is the use of a magnetic field (MF) and magnetic nanoparticles (NPs). Therefore, the type of NPs will be very effective.Methods: The performance of a cooling system using water/Fe3O4 and water/CoFe2O4 ferrofluids (FFs) under the MF was investigated and compared with water. The effects of different Reynolds numbers (200 to 1000), the MF intensity (0, 400, and 600 G), and a concentration of 0.5 vol% were investigated on heat transfer coefficient, Nusselt number (Nu), friction factor, and performance evaluation criterion (PEC).Significant Findings: Substituting FF instead of water increased the system's cooling performance so that at Re=400, without MF, Nu of CoFe2O4/water and Fe3O4/water FFs in comparison to water was increased by 10%, and 5.5%, respectively. So, without MF, CoFe2O4 NPs were more effective on heat transfer than the Fe3O4 NPs. In the presence of MF, Fe3O4 NPs were more effective than the CoFe2O4 NPs. So that the Nu of Fe3O4/water compared to water increases by 15% and 21%, respectively using the MF of 400 and 600 G. Generally, for all investigated cases, the highest PEC was obtained at Re=400.