The design and development of future in-space cryogenic storage and transfer systems depends on reliable, accurate models for two-phase boiling and heat transfer at low temperatures. Future systems…

Massachusetts Institute of Technology (MIT) has been awarded a $630,082 grant by the National Aeronautics and Space Administration (NASA) Shared Services Center to conduct research on cryogenic boiling and heat transfer at low temperatures. Over a three-year period, MIT will lead a team that includes NASA Glenn Research Center and Craft-Tech to carry out reduced gravity experiments using liquid nitrogen. The experiments aim to acquire fundamental data on cryogenic boiling parameters and develop reduced gravity computational fluid dynamics models. The models will enable accurate predictions of propellant boil-off during storage and estimates of chill-down times during propellant transfer, supporting the design of future in-space cryogenic propellant systems for NASA's Moon to Mars exploration missions. MIT will serve as the prime contractor, with work taking place in Cambridge, Massachusetts.

The design and development of future in-space cryogenic storage and transfer systems depends on reliable, accurate models for two-phase boiling and heat transfer at low temperatures. Future systems include nuclear thermal propulsion, ascent and descent stages, and propellant depots, all of which have cryogenic propellant tanks and transfer lines requiring accurate models of cryogenic boiling. The penalty for poor boiling models implies higher margins in launch propellant and higher safety factors, leading both to higher launch mass and cost. Currently, there exists few computational fluid dynamics model (CFD) for cryogenic storage and no reliable CFD models for cryogenic transfer line chill down and boiling within the united states. The gaps in the understanding of cryogenic boiling stem from the scarcity of high-resolution experimental data for the microscopic processes that initiate the nucleation, growth, development, and lift-off of bubbles, the formation and dynamics of the microlayer, and the subsequent heat exchange of bubbles with the bulk propellant. The variation of gravity further alters the fundamental boiling physics, exacerbating the complexity involved. We propose to carry out a series of fundamental reduced gravity experiments that will characterize cryogenic boiling heat transfer from the inception of nucleation sites to transition boiling and film boiling regimes resulting in a comprehensive multi-scale theoretical framework. These experiments have been made feasible by radical advances in high-resolution imaging techniques at MIT. Over the past several years, MIT has demonstrated in a laboratory environment the feasibility of leveraging two key imaging techniques, backlit shadowgraphy and total internal reflection (TIR), in combination with an indium tin oxide (ITO) heather, to visualize and measure fundamental boiling parameters such as nucleation site densities, bubble departure diameters, frequencies and characteristics of the microlayers and bubble footprints. The TIR method has demonstrated to be able to accurately segregate the different phases in contact with the boiling surface, with spatial resolutions of 10-50 microns/PX and framerates above 20,000 frames per second. This 2 year effort will use parabolic flight experiments to acquire the data needed to develop and validate reduced gravity CFD boiling models using liquid nitrogen as the working fluid. The effort will be led by researchers at MIT and supported by researchers at NASA glenn and craft-tech. The final outcome of the study will be to (1) gather the fundamental cryogenic boiling data in a reduced gravity environment, and (2) construct reduced gravity-based fundamental closure models of the microscopic boiling parameters that can be incorporated in macroscale CFD simulation methodology. This effort will enable accurate predictions of propellant boil off during storage, as well as estimation of chill down times during propellant transfer used to size and design future in-space cryogenic propellant systems for mission to the moon, mars, and in microgravity-based environments.