Cooling Performance Experiment and Simulation Investigation of Flow Boiling Heat Transfer for Wire Rods during Quenching in Molten Salt Mixtures

When the wire is cooled in the salt bath, since the wire temperature far exceeds the boiling point of the molten salt, accurately modeling the heat transfer process in molten salt quenching is difficult. Therefore, for investigating the cooling mechanism and improving the mechanical properties of wire rods, quenching experiments are conducted on specimens (92Si) at various molten salt (a 1:1 mixture of NaNO₃-KNO₃) temperatures using a salt bath furnace. Cooling curves are measured, and thus the real boiling heat transfer coefficient (HTC) at the metal–salt interface is calculated using a validated in-house-programmed inverse heat transfer algorithm based on experimental data. By integrating the experimentally determined boiling HTC with the convective HTC obtained from a salt bath simulation, a mathematical model of superposition flow boiling heat transfer is developed to predict the heat transfer characteristics, wire cooling behavior, and phase-transformation processes within the salt bath, which is also an innovation point of this article. The model effectively captures the actual heat transfer behavior during the early stages of salt bath quenching. The model is further used to evaluate the optimal molten salt temperature for quenching in a modified salt bath system with a flow rate of 60 m³ h⁻¹.