A modified force-balance model for prediction of bubble departure diameter in subcooled flow boiling

Experimental data by Sugrue et al., Klausner et al., Zeng et al., Prodanovic et al., and Situ et al. for bubble departure diameter in subcooled flow boiling in a wide range of orientation angle, subcooling, heat flux, mass flux, and pressure conditions were used to assess the predictive accuracy of the mechanistic force-balance models of Klausner et al. and Yun et al. The results suggested that both models capture the experimental trends correctly, but exhibit large average errors and standard deviations, i.e. 85.5% (σ = 49.7%) and 43.9% (σ = 23.1%) for Klausner's and Yun's models, respectively. Since the cube of the bubble departure diameter is used in subcooled flow boiling heat transfer models, such errors are unacceptable, and underscore the need for greater accuracy in predictions. Therefore, the databases were used to (i) identify the dominant forces determining bubble departure at various operating conditions, and (ii) optimize the empirical coefficients describing those forces in Klausner's model. The modified model considerably lowers prediction error to 22.4% (σ = 19.9%) for all data considered. Application of the modified model is demonstrated for the subcooled flow boiling conditions present in the hot channel of a typical Pressurized Water Reactor (PWR).