12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

This paper presents a CFD simulation study of the influence of roughness on the flow near stationary and rotating bath equipment. During production, the roughness of bath rolls is significantly increased by dross build-up. The latter is one major reason for undesired maintenance cycles. Understanding the interaction between roughness and zinc flow facilitates the interpretation of dross build-up growth mechanisms. The turbulent zinc alloy flow in the global zinc bath is computed with a k-w SST turbulence model. The flow, temperature and thermodynamics are mapped on a highly resolved sub-model, surrounding the rotating sink roll, with a sufficiently fine grid (y+ <1).The effect of roughness is modelled on this sub-model with the high roughness approach. The turbulence and roughness models are validated with measurement data from literature. It was found that flow velocity decreases significantly away from the rotating roll, with a decay of ~30% of the rotation velocity at a distance of 1mm. This steep velocity gradient is decreased by higher roughness. Rough peaks cause additional drag and increase the turbulent intensity. Thus, at higher roughness, the heat and mass-transfer towards the surface, where the growth of dross build-up occurs, is increased.