Heat transfer optimization in power-law ferrofluids under gravitational and microgravity conditions

This study examines the flow and thermal behavior of a power-law ferrofluid in a differentially heated enclosure containing a rectangular permanent magnet. The novelty of the present study lies in its exploration of the combined effects of magnetic and gravitational convection on the flow and thermal behavior of a power-law ferrofluid in the presence of a permanent magnet with varying aspect ratios. Unlike previous studies, this work specifically investigates how the magnet's aspect ratio, location, and the ferrofluid's rheological properties influence heat transfer, particularly in microgravity environments. Moreover, the study assesses the impact of the temperature number and the magnetic and gravitational Rayleigh numbers on the flow, temperature distribution, and Nusselt number variations. Findings indicate that strong gravitational effects can hinder magnetic convection, whereas, in microgravity conditions, heat transfer is maximized with a thin magnet (aspect ratio 1:9) in the cavity, yielding up to a 94 % increase in the average Nusselt number compared to a square magnet of the same volume. The average Nusselt number can increase up to four times by reducing the power-law index from 1.3 to 0.7, and by about 70 % when the magnet is moved towards the left hot wall compared to its central placement.