A Generalized Critical Heat Flux Correlation for Submerged and Free Surface Jet Impingement Boiling

Abstract

A G e n e ra liz e d C ritic a l H e a t F lu x C o rre la tio n fo r S u b m e rg e d and F ree S u rfa c e J e t Im p in g e m e n t B o ilin gA critical heat flux (CHF) correlation is developed fo r je t impingement boiling o f a single round je t on aflat circular surface. The correlation is valid fo r submerged jets as well as fo r free surface jets with Reynolds numbers (Re) between 4000 and 60,000. Data fo r the correlation are obtained from an extensive experimental study o f submerged je t impinge ment boiling performed by the authors with water at subatmospheric pressures and with FC-72 at atmospheric pressure. Additional experimental data from a free surface jet study are also incorporated to include the effect o f variation in surface diameter relative to a fixed nozzle diameter, additional working fluids (water and R-113 both at atmos pheric pressure), and jet configuration. The range o f parameters considered include Re from 0 (pool boiling) to 60,000, je t diameter to capillary length scale ratios (d/L c) rang ing from 0.44 to 5.50, surface diameter to capillary length scale ratios (dsILc) ranging from 4.47 to 38.42, and liquid-to-vapor density ratios from 119 to 8502. The proposed correlation is built on the framework o f a forced convective CHF model. Using this cor relation, 95% o f the experimental CHF je t impingement data can be predicted within ±22% error. The corresponding average absolute error and the maximum absolute error are 8% and 36%, respectively, over the range o f parameters considered. ObjectivesThe objective of the present work is to address the aforemen tioned deficiencies in literature for predicting jet impingement boiling CHF. A correlation stemming from a physical hydrody namic instability model of Haramura and Katto [2] is used to pre dict CHF over a wide range of fluidic and geometrical parameters.