Heat transfer by liquid jets impinging on a hot flat surface

Runout Table (ROT) cooling is one of the most important factors for controlling quality of hot rolled steel. ROT cooling uses large quantities of water to cool the steel plate. Optimizing heat transfer in the ROT would reduce the amount of water used, which will lower the amount of energy needed for pumping, filtering, storage and use of water. Optimization will therefore result in a direct energy saving as well as increasing the product quality. This study investigates heat transfer by turbulent water jets impinging on a hot flat steel plate at temperatures below the boiling point in order to understand convection heat transfer phenomena. This is an important stage that precedes the boiling and addresses the applicability of the heat transfer correlations available in the literature. A single axisymmetric jet and a pair of interacting jets are simulated using Computational Fluid Dynamics (CFD). The Reynolds Averaged Navier Stokes (RANS) model under steady and transient conditions and the k-epsilon turbulence model are used in both 2D axisymmetric and 3D simulations. We investigate the influence of the water flow rate on the jet cooling characteristics and develop a correlation for the radial position of the maximum Nusselt number based on numerical results. Two sets of boundary conditions - constant temperature and constant heat flux - are applied at the surface of the steel plate and evaluated. The single jet numerical results compare favourably with published data based on measurements and analytical models. The thermal performance of a two jet system was found to be no better than a single jet because the jets were too far from each other to generate any additional thermal interaction. (C) 2015 Elsevier Ltd. All rights reserved.