HEAT-TRANSFER DURING VAPOR BLANKET STAGE OF QUENCH

Although the production of a vapour blanket during the quenching of st eel components is well known, there has been little quantitative study of this phenomenon. At the same time there has been intensive investi gation of film boiling under other, better controlled conditions. The present work has applied certain mathematical models of film boiling t o the initial stages of a quench in both water and a polymer solution. This has allowed a comparison of the surface heat transfer coefficien ts obtained using these models with experimental data. For all models the calculated coefficients underestimate the experimental values, alt hough the reduction produced by the introduction of sodium polyacrylat e into the quenchant is demonstrated. Refinements to the original mode l, involving the use of a moving vapour/liquid interface and temperatu re dependent physical properties, produced only modest reductions in t he discrepancy between experiment and calculation. However, the availa ble models of film boiling assume laminar flow, whereas the experiment al evidence suggests that the liquid/vapour interface is turbulent. It is suggested that such a model would provide closer agreement with ex periment. Of critical importance is the velocity of the interface betw een the vapour and liquid, experimental measurements of which are lack ing. Further progress towards a quantitative understanding of the phen omena involved requires an experimental investigation of this paramete r. (C) 1993 The Institute of Materials.