Empirical Analysis and Optimization of Impingement Cooling-Jet-Geometry for Austempering Hot-Rolled Steel Using Computational Fluid Dynamics

Abstract

This investigation evaluates stationary impingement cooling of two bio-based fluids on a rectangular steel plate (230 × 120 × 12 mm) using jet diameters of 10 mm and 40 mm across impingement gaps of 115–155 mm. The study addresses the critical need for sustainable cooling media in metallurgical processes while advancing fundamental understanding of bio-fluid jet impingement heat transfer through integrated experimental-computational methodology. ANSYS-based numerical simulations and parametric optimization assessed how jet diameter and impingement gap influence convective heat transfer coefficients and governing dimensionless parameters. Temperature–time data were analysed using lumped thermal mass methods, generating empirical correlations from Reynolds, Nusselt, and Prandtl numbers. Key findings demonstrate that increased volumetric flow rate substantially enhances heat transfer at constant jet diameter, with heat transfer coefficients scaling proportionally with flow velocity. Experimental heat transfer coefficients ranged from 223–280W/m2K for palm kernel oil (PKO) and 251.22–360.24W/m2K for tiger-nut milk (TNM), with TNM demonstrating 25% superior performance attributed to its favourable thermophysical properties and enhanced momentum transfer characteristics. Numerical predictions yielded maximum heat fluxes of 18,657W/m2 and 21,117W/m2 for 10 mm and 40 mm jets, respectively. Measured values of 4,990.2W/m2 (PKO) and 6,736.4W/m2 (TNM) confirmed TNM’s enhanced cooling capacity, showing a 12% advantage at D = 40 mm. Experimental and computational results agreed reasonably, with 8–24% deviations validating the numerical model’s predictive capability. A major contribution is the development of an optimized correlation at D = 40 mm and H = 115 mm, Nu=hDK0.45Re0.56Pr0.13 which achieved 34% improvement in prediction accuracy over existing formulations for bio-based cooling fluids. These findings establish tiger-nut milk as a promising sustainable cooling medium for austempering hot-rolled steels, offering environmental benefits while maintaining thermal performance comparable to conventional quenchants.