A dry-spot model of critical heat flux applicable to both pool boiling andsubcooled forced convection boiling

A phenomenological model of critical heat flux (CHF) applicable to both poo r boiling and subcooled forced convection boiling is developed using the dr y-spot model proposed recently and existing correlations for active site de nsity, bubble departure diameter and heat transfer coefficient in nucleate boiling. For the active nucleation site density Kocamustafaogullari and Ish ii's model is used including the concept of a suppression factor. The Chen correlation is used for the estimation of total heat flux in nucleate boili ng. Comparisons of the model predictions with experimental data for pool bo iling of water and subcooled upward flow boiling of water in vertical, unif ormly-heated round tubes yield an averaged CHF ratio of 0.93 and a root-mea n-square error of 41.3%, The data set compared for CHF in subcooled forced convection boiling covers wide ranges of operating conditions (0.1 less tha n or equal to P less than or equal to 14.0 MPa, 0.00033 less than or equal to D less than or equal to 0.0375 m; 0.002 less than or equal to L less tha n or equal to 2 m; 660 less than or equal to G less than or equal to 90,000 kg/m(2) s; 70 less than or equal to Delta h(i) less than or equal to 1456 kJ/kg). By the modification of the suppression factor only the predictive c apability of the present model is greatly improved with a r.m.s. error of 2 0.5%. (C) 1999 Elsevier Science Ltd. All rights reserved.