Forced-convection boiling burnout for water in uniformly heated tubular test sections

Abstract

To thoroughly study the effects of the major variables in forced-convective burnout, 402 high-pressure critical heat flux determinations were made with seven uniformly heated, internally-cooled, tubular test sections using water, subcooled at the inlet, as the coolant. Data were collected over the following range of variables: Critical heat flux 0.44 to 2.57 × 10 6 Btu/hr-ft 2 Mass velocity 0.5 to 13.7 × 10 6 lb/hr-ft 2 Exit coolant conditions 116.6°F subcooled to 59.2% quality Pressure 500 to 1500 psia Heated length 24 to 77 5 8 in. Inside diameter 0.245 to 1.475 in. The 1.475 in. tube represents the largest tube ever tested. The results indicate the existence of three burnout regimes: nucleate boiling, annular flow, and the still not fully explored “transition” region. An analytical study of annular flow burnout based on observations and dimensional analysis yielded a correlation which relates the critical heat flux to the significant local fluid properties and flow parameters. This equation was used to correlate and study the critical heat flux data obtained in the present work together with a selection of additional data points from the major available sources, including data for freon-12. The equation contains four dimensionless groups and constants determined by regression analysis with a limited portion of the data. Critical heat fluxes calculated by the correlation are in good agreement with the measured values. Observations of the effects of the parameters in subcooled nucleate boiling burnout enabled the formulation of an empirical equation for this regime. The equation relates the critical heat flux only to the mass flow rate and subcooling. In testing the equation with available data it was found that the correlation holds throughout the 60 to 2000 psia pressure range equally well, thus implying that there is no pressure effect on subcooled burnout over this entire range. The complete form of this study, including tabulated data, correlating procedures, literature survey, etc., is available as ref. [1] of the bibliography.