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Analysis of water cooling process of steel strips on runout table Vakili, Soheyl


This study engages in the thermal analysis of water jet cooling of a hot moving steel strip on a run-out table. General 3D FE programs are developed for the direct and inverse heat transfer analysis. Studies show that gradient-based inverse algorithms suffer from high sensitivity to measurement noise and instability in small time steps. These two shortcomings limit their application in modeling of the real problems. Artificial neural network (ANN), genetic algorithm (GA), and particle swarm optimization (PSO) methods are applied to the inverse heat conduction problem in order to overcome the challenges faced by the gradient-based methods. Among them, GA and PSO are found to be effective. CRPSO, a variation of PSO, shows the best computational performance. However, compared to the gradient-based methods, these algorithms are very slow. Thus, a set of modifications were performed in this research to accelerate their convergence rate. Sequential formulation using the future time steps, multi-objective optimization, and inexact pre-evaluation using surrogate models are some of these modifications. Inverse analysis of experimental data shows that heat transfer behavior on the plate is mainly a function of the surface temperature, and can be categorized into three zones: High, mid, and low temperature. The effects of jet line configuration, jet line spacing, and plate moving speed were studied. The most uniform distribution happens in the case of fully staggered configuration. In higher jet line distances, the interaction effects become less significant, and a more uniform distribution is observed. The plate speed affects the heat transfer rate under the impingement point for the higher surface temperatures. In the high entry temperatures, the impingement heat transfer rate is lower when the plate is moving at a higher velocity. The plate speed does not significantly change the heat transfer behavior in the parallel flow zone. Finally, the results of the heat transfer analysis were coupled with the microstructure and structure fields, to study the thermal stresses and deflection occurring in the strips during the cooling process. It was found that fully-staggered jet configuration, larger spacing between jet lines, and lower plate speeds result in a less deformed steel strip.

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