CT-11 Two-Phase Pressure Drop Method for Vertical Downflow Intube Condensation: Data and Improvements

Z. H. Yang
1998; rev 09/2010

This report presents data and improvements to HTRI’s two-phase pressure drop method for vertical downflow intube condensation. HTRI’s previous two-phase flow pressure drop method was based on limited horizontal intube condensation data taken in the 1970s. That method predicts most pressure drop data within ± 30 percent. During 1995 and 1996, HTRI conducted more than 500 data runs on the Vertical Intube Condensation Unit (VICU); after analyzing and evaluating the data, we have improved the two-phase pressure drop method. HTRI has developed a modified correction factor for two-phase flow, C, for calculating friction pressure drop. This correction factor was correlated by the original theoretical Martinelli parameter, X (not the simplified Martinelli parameter, Xtt), and the density ratio of vapor to liquid. For two-phase momentum pressure drop calculation, HTRI has developed a new momentum recovery factor to correct momentum pressure drop for condensation in vacuum. The Premoli method for calculating liquid volume fraction, Rl, has been replaced by Turner and Wallis' model with HTRI’s empirical exponent function. Comparisons show that the improved two-phase pressure drop method gives very good predictions over a wide range of operating conditions.