Speaker
Description
Magnetohydrodynamic (MHD) convective flows have been well investigated theoretically and experimentally over the past few decades. However, studies on magneto-convection in closed geometries with heat transfer at internal obstacles has found less attention. In this work, we study the convective MHD flow in an engineering-relevant model geometry featuring a long rectangular cavity with a coaxial circular cooling pipe maintained at a constant temperature, with imposed volumetric heating in the fluid, to address this gap in the existing research. Temperature gradients that develop in the liquid metal drive a buoyant motion while Lorentz-forces caused by flow-induced currents oppose the flow. The magneto-convective flow is characterized mainly by a balance between the driving buoyant force, quantified in terms of the nondimensional Grashof number Gr, and the braking Lorentz force expressed by the Hartmann number Ha.
Previous numerical simulations with assumed fully established conditions along the axial direction revealed a magneto-convective motion in transverse planes, where a cold plume “falls down” below the cooling pipe. The present work shows that such flows could become unstable at sufficiently high Grashof numbers. With increasing magnetic field, the present 3D study finds a bifurcation and transition from the formerly 2D state towards complex 3D flow patterns with convection rolls then aligned preferentially with the transverse horizontal magnetic field. This transition from 2D flow pattern to 3D instabilities affects the convective heat transfer in terms of the Nusselt number Nu that is parametrically investigated depending on Gr and Ha.
Key Words: Magnetohydrodynamics (MHD), liquid metal heat transfer, magneto-convection, volumetric heating
Acknowledgment: This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.
