Thermal convection in liquid metal blankets for tokamak fusion reactors
[electronic resource].

Description

Main Author

Zhang, Xuan.

Language(s)

English

Published

2017-08-25.

Subjects

Magnetohydrodynamics.
Thermal convection.
Liquid metal blanket.

Summary

the flow within a poloidal (vertical) duct of a dual-coolant blanket, three regimes: steady-state, intermittent, or unstable with developed instability, are found at different parameters. The results of a parametric study show that the flow behavior is dominated by the buoyancy effect and magnetic damping together. At the conditions close to those of a fusion reactor, the flow is likely to be unstable with developed instability. Temperature fluctuations appear in the flow, which is detrimental to the blanket operation.
at parameters close to the conditions of a real fusion reactor. A weaker (5% in amplitude of the axial component) vertical magnetic field (induced by 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 reveals that 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 develops strong thermal convection in the transverse plane at moderate Grashof numbers. At large Grashof numbers, the flow is dominated by the top-bottom asymmetry of the streamwise velocity and stable stratification of temperature, which are caused by the buoyancy force due to the mean temperature growing along the duct. This leads to suppression of thermal convection, weak mixing, and substantial gradients of wall temperature. In
Thermal convection in liquid metal flows with strong heating and strong imposed magnetic fields 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 blankets of fusion reactors. Models related to two types of the blankets are explored: a separately cooled blanket with walls maintained at constant temperature and no significant mean flow along the duct and a dual-coolant blanket with thermally insulating walls and non-negligible mean flow. The results for three configurations of a toroidal duct and one configurations of a poloidal duct are presented. In the flow within a toroidal (horizontal) duct of a separately cooled blanket, turbulent convection appears at high Grashof number when the magnetic field is purely axial. Flow maintains good two-dimensionality

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