Thermal convection in liquid metal blankets for tokamak fusion reactors

Magnetohydrodynamics;Thermal convection;Liquid metal blanket;Automotive Systems Engineering;Automotive Systems Engineering, College of Engineering and Computer Science

Zhang, XuanMohanty, Pravansu ;

University of Michigan

关键词: Magnetohydrodynamics;    Thermal convection;    Liquid metal blanket;    Automotive Systems Engineering;    Automotive Systems Engineering, College of Engineering and Computer Science;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/136199/Dissertation_Xuan%20Zhang%20FINAL.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Thermal convection in liquid metal flows with strong heating and strong imposed magneticfields is studied numerically using the method of direct numerical simulation (DNS).The goal is to understand the effect of convection in ducts of conceptual liquid metal blanketsof fusion reactors. Models related to two types of the blankets are explored: a separatelycooled blanket with walls maintained at constant temperature and no significantmean flow along the duct and a dual-coolant blanket with thermally insulating walls andnon-negligible mean flow. The results for three configurations of a toroidal duct and oneconfigurations of a poloidal duct are presented.In the flow within a toroidal (horizontal) duct of a separately cooled blanket, turbulentconvection appears at high Grashof number when the magnetic field is purely axial. Flowmaintains good two-dimensionality at parameters close to the conditions of a real fusion reactor.A weaker (5% in amplitude of the axial component) vertical magnetic field (inducedby the currents in the plasma) suppresses the turbulence, elongates convection structures,and leads to formation of strong shear layers and near-wall jets. Stability analysis revealsthat the transformation makes the flow more unstable to three-dimensional perturbations.In the flow within a toroidal (horizontal) duct of a dual-coolant blanket, the flow developsstrong thermal convection in the transverse plane at moderate Grashof numbers. At largeGrashof numbers, the flow is dominated by the top-bottom asymmetry of the streamwisevelocity and stable stratification of temperature, which are caused by the buoyancy forcedue to the mean temperature growing along the duct. This leads to suppression of thermalconvection, weak mixing, and substantial gradients of wall temperature. In the flow withina poloidal (vertical) duct of a dual-coolant blanket, three regimes: steady-state, intermittent,or unstable with developed instability, are found at different parameters. The resultsof a parametric study show that the flow behavior is dominated by the buoyancy effect andmagnetic damping together. At the conditions close to those of a fusion reactor, the flowis likely to be unstable with developed instability. Temperature fluctuations appear in theflow, which is detrimental to the blanket operation.