Modulation of the wall-heat transfer in turbulent thermomagnetic convection by magnetic field gradients

We present combined experimental and numerical studies of the heat transfer of paramagnetic or diamagnetic fluid inside a differentially heated cubical enclosure subjected to the magnetic field gradients of different strength and orientation. In contrast to the previously reported studies in literature, which observed solely laminar flow regimes, here we focused on the fully developed turbulent flow regimes. That was possible by using a combination of the state-of-art superconducting magnets (with a strength up to 10 T and magnetic field gradients up to 900 T2/m) and by selecting various paramagnetic or diamagnetic working fluids (in a range of 10 Pr 1000). Detailed comparison between experiments (integral wall-heat transfer, temperature time-series at different locations within the enclosure) and direct numerical simulations (DNS) are performed and generally very good agreements are obtained in predicting the integral heat transfer. In addition, analysis of the long-term averaged first- and second-moments of velocity and thermal fields is performed. Finally, budgets of the turbulent kinetic energy and of the temperature variance are analyzed and the mean mechanism of the thermal plume reorganization in terms of the proper-orthogonal decomposition (POD) modes is presented.Chemical EngineeringApplied Science

Oscillatory states in thermal convection of a paramagnetic fluid in a cubical enclosure subjected to a magnetic field gradient

We report experimental and numerical studies of combined natural and magnetic convection of a paramagnetic fluid inside a cubical enclosure heated from below and cooled from above and subjected to a magnetic field gradient. Values of the magnetic field gradient are in the range 9?|grad|b0|2|?900 T2/m for imposed magnetic field strengths in the center of the superconducting magnet bore of 1?|b0|max?10 T. Very good agreement between experiments and simulation is obtained in predicting the integral heat transfer over the entire range of working parameters (i.e., thermal Rayleigh number 1.15×105?RaT?8×106, Prandtl number 5?Pr?700, and magnetization number 0???58.5). We present a stability diagram containing three characteristic states: steady, oscillatory (periodic), and turbulent regimes. The oscillatory states are identified for intermediate values of Pr (40?Pr?70) and low magnetic field (|b0|max?2 T). Turbulent states are generated from initially stable flow and heat transfer regimes in the range of 70?Pr?500 for sufficiently strong magnetic field (|b0|max?4 T).MSP/Multi-Scale PhysicsApplied Science

Transients and turbulence pockets in thermal convection of paramagnetic fluid subjected to strong magnetic field gradients

We performed combined experimental and numerical studies of the flow and heat transfer of a paramagnetic fluid inside a differentially heated cubical enclosure subjected to various strong non-uniform magnetic field gradients. Two different heating scenarios are considered: unstable (heated from below) and stable (heated from above) initial thermal stratification. In contrast to the previously reported studies in literature, which observed solely laminar flow regimes, we investigated also appearance and sustenance of the periodic- and fully transient-flow motions for the very first time. This was consequence of using significantly stronger magnetic field strength (up to 10 T experimentally, and up to 15 T numerically) than those used in previous studies (up to 5 T). Detailed comparison between experiments and numerical simulations are performed and generally very good agreements were obtained.Chemical EngineeringApplied Science