Description: The technical objective is to develop versatile boiling models that are applicable to a broad class of cryogenic fluids of interest to NASA. Furthermore these boiling models would be valid over a wide range of gravitational effects as well and could be applied from zero-g to 1-g conditions. The models would be developed by obtaining cryogenic pool boiling test data both at ground (1g )and flight (low gravity) conditions. The pool boiling flight test rig will be flown on two parabolic flights to obtain low gravity data for liquid nitrogen. Test data will be obtained both at ultra-low velocity as well as high velocity regimes. Ground tests at MIT will be conducted for different cryogens to supplement earlier data taken for liquid nitrogen. The experimental test data obtained over a broad range of cryogenic fluids, gravity levels and velocity scales will be processed with machine learning techniques to develop closure models for key boiling model parameters such bubble departure diameter, frequency, and nucleation site density. It would allow for effects such wettability, substrate surface properties, microlayer dynamics and bubble sliding effects. The enhanced boiling model will be implemented in a CFD code and line chilldown for liquid nitrogen and liquid hydrogen will be simulated and compared with available quenching data obtained at NASA GRC. Support will be provided for incorporating the new enhanced model into CFD codes used by NASA by providing the details of the CFD formulation for the new cryogenic boiling model.

Benefits: Reliable and effective cryogenic propellant storage and transfer are integral to nearly all of propulsion and life support systems that will be required in NASA’s future human exploration missions. The tools developed here can result in efficient and reliable protocols for propellant transfer addressing important needs for such missions from launch, in-space engine start-up to orbital refueling. Furthermore, improved pool boiling and flow boiling models impact several key elements of cryogenic fluid management and help reduce propellant loss.

The projected growth of a hydrogen economy in the near future will require accurate and reliable cryogenic modeling tools for transport, distribution and long term storage of liquid hydrogen. Projected uses range from energy storage for renewal energy (wind and solar) plants, hydrogen turbines and aircraft propulsion with liquid hydrogen fuel as well as increased commercial launch activities.