Efficient Models for Film Condensation in Cryogenic Tank Applications

NASA’s long duration human space exploration plans to the moon, and later mars, require the design and maturation of hardware for propellant replenishment technologies such as in-space tank-to-tank transfer from a fuel depot and liquid propellant production through In-Situ Resource Utilization (ISRU). Currently CFD tools required to support the design of these systems, with complex condensation phase change features, are not sufficiently mature either in their accuracy or numerical efficiency to be useful within design cycle timelines. The innovation proposed here is the development of accurate sub-grid CFD models for modeling condensation in cryogens, on coarse grids, that provide condensate estimates of film thickness within 25% accuracy and with numerical speed-up of an order of magnitude. The framework proposed captures growth and transport of liquid layer along wall boundary while conserving mass, momentum and energy as part of continuum numerical framework. The model was validated for condensation on a vertical flat plate for three cryogenic fluid including methane, nitrogen and oxygen. Test data for oxygen condensation with enhanced experimental techniques and additional instrumentation was obtained as part of this effort. The proposed effort will extend the database for oxygen condensation by conducting parametric studies over a broad range of temperatures and pressures, as well as orientations of the plate to vary the effect of gravity. Test data for oxygen condensation in a sub-scale tank will be obtained and used for validating the model for complex three-dimensional configurations. The well validated CFD framework can be used for design support and optimization of hardware for in-space tank-to-tank transfer in NASA’s Artemis program. as well as liquid propellant production through In-Situ Resource Utilization (ISRU) for future Mars missions.

The technology developed here is relevant to the design support needs of the Artemis III mission; NASA’s first human mission to the lunar south pole which envisions in-space transfer of propellant from storage depots to the human landing system. In-space replenishment of propellants will require the development of efficient methods and protocols to transfer these cryogenic propellants from the storage depots to receiving tanks on-board the spacecraft. The demand for conserving propellant during refueling in space requires that the transfer process be optimized to achieve high fill fractions and minimize propellant loss to boil-off and venting while being constrained by the maximum allowable working pressure of the receiving tank. Effective cryogenic fluid management will utilize liquification of the cryogens to reduce the storage volume and provide a means of pressure control which is vital when conducting tank transfer operations. In-Situ-Resource-Utilization (ISRU) is another key NASA technology area particularly for Mars travel where cryogenic fluids such as hydrogen, methane, and oxygen will have to be produced, liquefied, and stored to make these missions successful. Due to the high density of liquid oxygen, the ability to liquefy oxygen in particular has been identified by NASA as critical need to obtain the maximum benefit of weight reduction and payload increase in the Mars Ascent Vehicle (MAV). Data for oxygen liquefaction in a sub-scale tank planned as part of this effort will directly support NASA’s CRYOFILL test program by providing a test bed for evaluating experimental procedure and risk mitigation for oxygen liquefaction in preparation for the larger scale tanks that are scheduled to be tested in the CRYOFILL program. Cryogenic Fluid Management affects varied space-exploration initiatives and as the commercial space launch market continues to grow the market for high-fidelity cryogenic fluid management 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. The market segment for commercial aircraft with hydrogen propulsion is also an emerging market. The proposed aircraft models include turbofan, turboprop and blended wing body (BWB) designs. In all these designs liquid hydrogen is stored on-board and distributed to hybrid hydrogen turbo-fan engines. The storage and distribution of cryogenic propellants in these systems represents a direct opportunity for our product being developed here.

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