Inversion of flow and heat transfer of the paramagnetic fluid in a differentially heated cube

The present study addresses the detailed numerical analysis of the flow and heat transfer of a paramagnetic fluid inside a differentially heated cubical box and subjected to a strong non-uniform magnetic field. Two different heating scenarios are considered regarding an initial thermal stratification: unstable (heated from the bottom) and stable (heated from the top), both subjected to the same magnetic field. For a fixed value of the thermal Rayleigh number (Ra=1.4×10⁵) integral heat transfer is measured over a range of imposed magnetic fields, 0 ≤ |b₀|_max ≤ 10 T. To obtain detailed insights into local wall-heat transfer and its dependency on the flow patterns generated, numerical simulations of the experimental setup are performed. A relatively good agreement between experiments and numerical simulations is obtained in predicting the integral heat transfer (with an averaged ΔNu¯<7% over the entire range of working parameters for both heating configurations). It is demonstrated that a strong convective motion can be generated under the influence of the magnetization force even for the heated-from-above situation that initially was in the pure conduction state. This magnetically assisted (heated from the bottom) and magnetically inverted (heated from the top) Rayleigh-Bénard convection produced up to 5 and 15 times more efficient heat transfer compared to the initial neutral situation, respectively.