Numerical Investigation of an Impingement Flow due to a Free Surface Axisymmetric Long Water Jet

Abstract

The hydrodynamics of impingement flow is a key partner of heat transfer analysis of run-out table (ROT) cooling. The long circular free-surface water jets with industrial parameters (e.g. Re = 16,000–50,000) were numerically simulated by laminar and two variants of turbulent k-ε and k-ω models where the effect of gravity is significant. The development of water impingement film was computed and compared with the experimental data which obtained from the ROT facility. The propagation of water flow over the impingement surface is better simulated by Shear Stress transition k-ω (SST) model. The impingement flow features such as jet deceleration before hitting wall and velocity and pressure profiles were compared with short jet data to explore common flow characteristics between the short and long jets. The effect of target surface on retardation of long turbulent liquid jet before incident is pronouncing as jet Reynolds number increased. However, the velocity reduction is not noticeable until where the speed of short jet starts decreasing. In impingement zone, the flow radial velocity varies linearly similar to short liquid jets which gravity effect is neglected. But, the velocity gradient was found higher which shows enhanced heat transfer for a long turbulent water jet. The dimension of impingement zone as an influential region in boiling heat transfer analysis is found smaller respect to the estimation which used in ROT modeling. The effect of local impingement pressure on saturation temperature is found important in stagnation zone which influences the prediction of heat fluxes by boiling heat transfer correlations up to 9%. This has to be considered in ROT modeling where the heat flux can be as high as 10 Mw/m2.