Pitch-to-diameter effect on two-phase flow across an in-line tube bundle

Void fraction and friction pressure drop measurements were made for an adiabatic, vertical two‐phase flow of air‐water across two horizontal, in‐line, 5 × 20 rod bundles, one with a pitch‐to‐diameter ratio, P/D, of 1.3, the other 1.75. For both bundles the average void fraction showed a strong mass velocity effect and values were significantly less than those predicted by a homogeneous flow model. All void fraction data were found to be well correlated, with no P/D effect, using the dimensionless gas velocity, j*g. The two‐phase friction multiplier data exhibited a strong effect of P/D and mass velocity, however, the data for both bundles could be well correlated with the Martinelli parameter for G > 200 kg/m2s. The correlations developed for void fraction and two‐phase friction multiplier were successfully tested in predicting the total pressure drop in boiling freon experiments.