TPF-1 Summary and Evaluation of Void Fraction Correlations
The HTFS Report DR-15, Section B, "Void Fractions," was reviewed and the main conclusions summarized. Void fraction is defined as the ratio of local vapor volume to total flow volume in a cross-section and is a necessary relation for calculation of average density in a two-phase system.
Twenty-one void fraction correlations from the literature were tested against a data bank of 5,600 points. The accuracies of prediction were found to depend on the ranges of densities, quality, mass velocity, viscosity and orientation. Seven equations are recommended on the basis of best prediction in different ranges of these parameters (see Section 4 and Fig. 4-1 or more detailed recommendation in Appendix A).
Over the usual range of conditions encountered, many of the correlations were found to give similar results. The correlation of Premoli, Eq. 3-28, was selected by HTFS as having the best overall accuracy. A comparison of results from this method with the results from other methods in common use was made for selected cases.