Film and transition boiling correlations for quenching of hot surfaces with water sprays

Abstract

Using a miniature gold plated copper disk as target, quenching experiments were performed with water sprays to correlate heat fluxq′’ to surface-to-fluid temperature difference AT, and the local values for the spray hydrodynamic parameters of volumetric fluxQ′’, mean drop velocityUm and Sauter mean drop diameterd32 over a wide range of operating conditions (Q′’ = 0.58 x 10−3−9.96 x 10−3 m3 sec−1/m2,Um = 10.1-29.9 m/sec,d32 = 0.137-1.350 mm), and surface temperatures up to 520° C. Drop diameter was found to have a weak effect on heat transfer in film boiling for all the conditions tested. Two distinct spray cooling regimes were identified, allowing the classification of sprays with respect to volumetric flux, low flux sprays forQ″ 3.5 x 10−3 m3 sec−1/m2. WhileQ″ had a significant influence on film boiling in both regimes, drop velocity was important only for the high flux sprays. A spray quenching test bed was also constructed to simulate, under controlled laboratory conditions, spray quenching of alloys in an industrial environment. The test bed was used to generate temperature-time records for a rectangular aluminum plate during spray quenching. Using the software package ANSYS, the measured temperature response was successfully simulated by utilizing the newly developed boiling correlations in defining boundary conditions for the quenched surface after accounting for spatial variations in the hydrodynamic parameters within the spray field. The effectiveness of this numerical technique for the tested configuration is proof that it may be possible to predict the temperature-time history for quenched parts with complicated shapes provided the spatial distributions of the hydrodynamic parameters are well mapped or predetermined.