Efficient Models for Film Condensation in Cryogenic Tank Applications

To support NASA’s Cryogenic Fluid Management (CFM) design and operation initiatives subgrid computational fluid dynamics (CFD) models of cryogenic condensation/liquification are required to allow for efficient trade studies to be conducted on real systems over a range of conditions that may be prohibitive with laboratory testing. In the Phase I effort, a validated subgrid CFD model of cryogenic film condensation on a vertical flat wall will be developed which is capable of capturing the formation and growth of a cryogenic condensation layer and its movement along a wall boundary. A systematic test campaign will be undertaken to investigate the downflow film condensation of oxygen which is of relevance to CFM and In-Situ Resource Utilization (ISRU) initiatives. The Phase I test effort emphasizes experimental visualization of the onset of film condensation, understanding of relative importance of heat transfer processes, quantification of key film characteristics, including liquid film thickness, vapor thermal boundary layer, and condensation heat flux, and identification of governing parameters that influence cryogenic film formation and growth. The experimental data will be used for fundamental validation of a subgrid cryogenic film condensation CFD phase-change model, setting the stage for a Phase II validation program on prototype CFM geometries. The Phase II effort will extend the validation to tank geometries and incorporate the validated film condensation model into commercial CFD tools used by NASA. The validated predictive simulation tools will help in identifying better designs and protocols related to cryogenic propellant transfer and ISRU thereby mitigating risk in outer space hardware deployment and operational strategies.

To support NASA Cryogenic fluid management (CFM) and In-Situ-Resource-Utilization (ISRU) design and operation initiatives, computational fluid dynamics (CFD) models of cryogenic condensation/liquification are required to allow for trade studies to be conducted and minimize reliance on more expensive laboratory testing. A key component of predictive CFD tools for CFM/ISRU will be the ability to accurately model condensation of cryogenic fluids on cold surfaces at varying operating conditions and orientations. Here, development and application of subgrid CFD models to capture the formation and growth of a liquid condensation layer without fully resolving the developing layer is essential to provide the necessary computational efficiency required for practical system-level studies. In addition, the extremely low boiling temperatures of cryogens challenges fundamental studies and data acquisition, and to date CFD models for predicting cryogenic film condensation are largely unvalidated. Thus, the reliability of current predictive CFD tools for CFM/ISRU is inadequate considering the slim margins that are inherent in the successful production, storage, and transfer of cryogenic fluids of interest to NASA’s space exploration mission. The proposed effort is designed to fill this gap in CFM/ISRU by developing a subgrid condensation model to interface with a Volume-of-Fluid (VOF) scheme that is used to model the bulk liquid/vapor phases, collecting fundamental laboratory data on the condensation of cryogenic gases, and using the collected data to calibrate/validate the CFD framework for cryogenic liquification that can then be used in CFM studies of proposed systems and procedures to support NASA’s space exploration goals. Cryogenic Fluid Management affects many space-exploration initiatives and as the commercial space launch market continues to grow the market for high-fidelity cryogenic simulation software will expand to support design and operational strategies. Industries involved in liquefied gases, hydrogen as a green fuel, and the petroleum industry with liquefied natural gas also provide a potential market.

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