Analytical and numerical determination of the heat transfer coefficient between scrap and hot metal based on small-scale experiments

•Experimental Investigation of the heat transfer coefficients.•Coefficients achieved approx. 10x smaller than calculated with Nusselt correlations.•Explicit numerical model for heat transfer in scrap melting was developed. Dynamic modelling of the Linz-Donawitz oxygen steelmaking process (LD) is one of the most challenging tasks in the current economic situation for the optimization of integrated steel plants. One of the main influencing parameters is the melting and dissolution behaviour of scrap. Scrap is used as an iron source and coolant for the exothermic reactions inside the LD converter. Literature-based dissolution equations are commonly used in modelling. As a basis for developing a new numerical model for scrap melting with coupled heat and mass transfer, laboratory-scale experiments were conducted. The aim of the experiments was the determination of the heat transfer coefficient between scrap and liquid hot metal through a combination of thermocouple measurements with analytical and numerical solutions. The heat transfer coefficients achieved were in the range between 4.5 and 6.2 kW/m2 K. The heat transfer coefficients estimated in the present work are approximately 10 times smaller than those evaluated through existing Nusselt correlations. These discrepancies may be explainable through specific effects of scrap dissolution, e.g. shell freezing and successive melting or air-gap formation between solidified shell and mother scrap increasing the heat transfer resistance at the solid scrap to melt interface. The numerical solution to the heat transfer problem shows identical results to the analytical solution of the problem and provides a feasible basis for further research and development.