Two-phase pressure drop of air-water in small horizontal tubes

Two-phase flow pressure drops of air-water in small horizontal smooth tubes of 1.02, 3.17, 5.05, and 7.02 rum are reported. The data are compared with homogeneous, slug, and annular flow models, as well as the commonly used e mpirical correlations. The tested results indicate that the empirical corre lations available in the literature failed to predict the data. The slug fl ow and annular flow models give fair predictions with their corresponding f low regime data. The homogeneous model shows better predictive ability as c ompared to other empirical correlations. However, overpredictions of homoge neous and annular models are observed for most of the 1.02- and 3.17-mm dat a. Thus, modifications of the homogeneous model and the Friedel correlation are made by introducing the Bond number, Weber number, and other significa nt dimensionless groups to correlate the test data. The modified Friedel co rrelations and the modified homogeneous model show good agreement with the present data, as well as with five available data sets of ammonia and refri gerants from the literature.