Simulation of Chilldown Process with a Sub-Grid Boiling Model

The process of chilling propellant transfer lines, before ignition of liquid rocket engines is initiated is a critical step before launch and in-space propulsion. Similarly, reliable engine operations, require flow to be conditioned, devoid of two-phase content and pool/flow boiling considerations impact cryogenic tank propellant management. The chilling/quenching of propellant lines undergo complex flow patterns involving film boiling, transition boiling, nucleate boiling and single phase convective heat transfer. In Phase I, a mesoscopic boiling model was integrated into a high-fidelity multi-physics simulation framework and quenching of vertical tubes with cryogenic fluids under terrestrial and microgravity conditions were demonstrated. In Phase II, experiments providing data of important sub-model closures involving bubble departure diameter, frequency and nucleation site density for cryogenic fluids are planned.nbsp; These measurements aided with machine learning algorithms will help in improving the accuracy of correlations and closure models.nbsp; Furthermore, the boiling model will be enhanced involving additional physics related to surface wettability, bubble sliding effects, solid wall quenching etc along with substrate roughness that affects convective heat transfer and nucleation.nbsp; Detailed validation studies are planned with hydrogen and nitrogen under normal gravity and microgravity conditions and boiling model framework will be ported to NASArsquo;s codes to support mission related activities.