Universal Critical Heat Flux (CHF) Correlations for Cryogenic Flow Boiling in Uniformly Heated Tubes

Abstract

Experiments to determine critical heat flux (CHF) for cryogen flow in uniformly heated, round tubes have been performed throughout the globe during the past sixty years. However, experimental CHF data for cryogens are rarely published, 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) Cryogen Flow Boiling CHF Database is consolidated from world literature dating back to 1959. With 2312 data points for LH2, LHe, LN2 and LCH4, it represents the largest cryogen CHF database assembled to date. The database encompasses diameters from 0.5 to 14.1 mm, critical length-to-diameter ratios from 2.5 to 230.8 (term ‘critical’ refers to axial location where CHF is detected), system pressures from 0.01 to 4.07 MPa, reduced pressures from 0.1 to 0.93, mass velocities from 2.2 to 8203.9 kg m−2 s−1, inlet subcoolings from 0 to 78.9 K, inlet qualities from -2.06 to 0.95, critical subcoolings from 0 to 48.5 K, critical qualities from -1.23 to 1.00, critical void fractions from 0 to 1, and CHF values from 0.05 to 8203.9 kW m−2. The consolidated database represents an invaluable tool for development of CHF correlations – a primary goal for the present study – as well as future analytic and computational models. Using this database, new universal CHF correlations are constructed for two distinct CHF mechanisms, Departure from Nucleate Boiling (DNB) and Dryout, after careful physics-based segregation of the data. With mean absolute errors below 30%, the new CHF correlations are shown to provide good predictive agreement with the database.