MODELLING HEAT TRANSFER PROCESSES DURING STEEL QUENCHING USING COMSOL MULTIPHYSICS

Abstract

In the present work, modelling transient heat transfer during quenching of a hot cylindrical probe submerged in a water tank has been studied using the commercial finite element software ComsolMultiphysics. During the quenching process, heat is transferred rapidly from the hot metal component to the quenchant and the rapid temperature drop introduces phase transformation and deformation in the component. Standardized methodology of studying the fundamental heat transfer mechanisms between the quenchant and the quenching probe, were adopted using the lumped capacitance analysis for deriving heat transfer coefficient. The heat transfer model takes into account different stages in quenching the steel probe from film boiling at very high work piece surface temperatures, to nucleate boiling stage during which heat removal rate from the hot surface is the highest, and finally the single-phase convection at surface temperatures below saturation. In order to reduce computation time and complexity, 2D symmetric and 2D asymmetric models were applied to model conduction, convection and radiation heat transfer processes during quenching. Computational Fluid Dynamics (CFD) and conjugate heat transfer physics that couples vapour dynamics, energy conservation of the liquid phase and heat transferred from the quenched probe were used. The computed heat transfer during vapour bubble growth around the test probe was reported. The results show that the flow pattern dramatically changes with a decrease in the surface temperature which implies that the surface of the component cools down faster than the core due to large thermal gradients.