Heat transfer during vapour blanket stage of quench

Abstract

Although the production of a vapour blanket during the quenching of steel components is well known, there has been little quantitative study of this phenomenon. At the same time there has been intensive investigation of film boiling under other, better controlled conditions. The present work has applied certain mathematical models of film boiling to the initial stages of a quench in both water and a polymer solution. This has allowed a comparison of the surface heat transfer coefficients obtained using these models with experimental data. For all models the calculated coefficients underestimate the experimental values, although the reduction produced by the introduction of sodium polyacrylate into the quenchant is demonstrated. Refinements to the original model, involving the use of a moving vapour/liquid interface and temperature dependent physical properties, produced only modest reductions in the discrepancy between experiment and calculation. However, the available models of film boiling assume laminar flow, whereas the experimental evidence suggests that the liquid/vapour interface is turbulent. It is suggested that such a model would provide closer agreement with experiment. Of critical importance is the velocity of the interface between the vapour and liquid, experimental measurements of which are lacking. Further progress towards a quantitative understanding of the phenomena involved requires an experimental investigation of this parameter.

MST/1815