Study of Jet Impingement Cooling Behaviour of Hot Steel Plate in Film Boiling Regime Using CFD

Abstract

Liquid jet impingement cooling is critical in many industrial applications. Impingement water jets are used as a fast cooling system ( ≈ 85°C/s) for hot steel plates, because of the high extracted heat flux (≈ 10 MW/m2). Due to the complexity of the process, the mechanism of flow boiling heat transfer during jet impingement cooling is not well understood. The principle challenge in the study of jet impingement cooling for these high-temperature applications has been the lack of reliable instrumentation for measuring the cooling rates. The aim of this work is to perform numerical study of jet impingement quenching of hot steel plates with conditions comparable to the actual experimental data in the literature using Ansys Fluent. This study presents a systematic methodology for the estimation of various hydrodynamic parameters and thermal variation of heat flux on the impingement surface during jet impingement cooling of extremely hot steel plate using CFD. The simulated results obtained for hydrodynamic parameters of 2D and 3D computational models for impinging jet reported a good agreement with the available correlations and experimental data. The Impinging jet velocity (Vj), Impingement jet diameter (Dj) and radial location of Hydraulic jump (Rhj) increases with increasing inlet velocity at the nozzle (VN). Simulated results for quenching of hot steel plate at Ti = 900ºC gives cooling and boiling curves at different radial location on the surface of the plate. A gradually growing circular wetted region, with its periphery named as the wetting front, forms soon after the cooling starts but its velocity decreases as it grows in diameter. A local maximum in the surface heat flux closely follows the wetting front, with the local maximum heat flux reducing with distance from the stagnation point. The temperature drop (cooling rate) is higher at the stagnation point and decreases with increasing radial location from the stagnation point. The heat flux and CHF are higher in the stagnation zone than in other zones because of greater subcooling of the impinging water jet in the stagnation zone.