Effects of rotation angle and metal foam on natural convection of nanofluids in a cavity under an adjustable magnetic field

To investigate the natural convection heat transfer of Fe3O4-water nanofluids in a rectangular cavity under an adjustable magnetic field, two experimental systems are established. Meanwhile, several factors, such as nanoparticle mass fractions (omega = 0%, 0.1%, 0.3%, 0.5%), magnetic field directions (horizontal and vertical), magnetic field intensities (B = 0.0 T, 0.01 T, 0.02 T), rotation angles of the cavity (alpha = 0 degrees, 45 degrees, 90 degrees, 135 degrees), and PPI of Cu metal foam (PPI = 0, 5, 15) are taken into consideration to research the natural convection of Fe3O4 water nanofluids in a rectangular cavity. With the increasing nanoparticle mass fraction, Nusselt number firstly rises but then falls, and the maximum value of which appears at a nanoparticle mass fraction omega = 0.3%. Horizontal magnetic field is not significant to the thermal performance enhancement, but vertical magnetic field shows an opposite trend and makes a positive contribution to the thermal performance. The cavity with a rotation angle alpha = 90 degrees shows the highest thermal performance. Nusselt number of the cavity filled with metal foam can be improved obviously compared with that without metal foam. But the increasing PPI of metal foam is disadvantageous to heat transfer performance.