Development of Two-Phase Frictional Pressure Gradient Correlation for Saturated Cryogenic Flow Boiling in Uniformly Heated Tubes

Experiments to determine two-phase frictional pressure drop for saturated cryogenic flow boiling in uniformly heated round tubes have been performed throughout the globe during the past sixty years for a variety of cryogens. However, the experimental data are scarce and either rarely published or published only for a few cryogens, with majority of the data remaining in the archives of authors, or in obscure technical reports of an organization or other inaccessible sources. In the present study, the Purdue University-Boiling and Two-Phase Flow Laboratory (PU-BTPFL) Cryogenic Total Pressure Drop Database is consolidated both for saturated adiabatic liquid-vapor and saturated flow boiling for cryogens from world literature dating back to 1964. With 474 total pressure drop data points for LHe, LH2, LNe, and LN2, it represents the largest total pressure drop database for cryogenic saturated two-phase flow assembled to date. Using this database, predictive accuracy of seminal frictional pressure gradient correlations employing both the Homogenous Equilibrium Model (HEM) and the Separated Flow Model (SFM) are assessed. The distinct fluid physics unique to cryogens is studied further using the database and new dimensionless criteria are developed to demarcate a dispersed flow dominant data subset from the separated flow dominant data subset, which are better represented using HEM and SFM, respectively. These criteria are subsequently used to develop a hybrid HEM-SEM frictional pressure gradient correlation for saturated cryogenic flow for the two distinct data subsets. The new hybrid correlation performs the best of all seminal correlations and provides excellent predictive agreement with the database, evidenced by a Mean Absolute Error (MAE) of 14.7 %.