Hastings, L.J. | Search NASA

NASA NTRS2007

Analyzing the Use of Gaseous Helium as a Pressurant with Cryogenic Propellants with Thermodynamic Venting System Modelling and Test Data

Cryogens are viable candidate propellants for NASA's Lunar and Mars exploration programs. To provide adequate mass flow to the system's engines and/or to prevent feed system cavitation, gaseous helium (GHe) is frequently considered as a pressurant. During low gravity operations, a Thermodynamic Venting System (TVS) is designed to maintain tank pressure during low gravity operations without propellant resettling. Therefore, a series of tests were conducted in the Multi-purpose Hydrogen Test Bed (MHTB) of Marshall Space Flight Center (MSFC) in order to evaluate the effects of GHe pressurant on pressure control performance of a TVS with liquid hydrogen (LH2) and nitrogen (LN2) as the test liquids. The TVS used in these test series consists of a recirculation pump, Joule-Thomson (J-T) expansion valve, and a parallel flow concentric tube heat exchanger combined with a longitudinal spray bar. Using a small amount of liquid extracted from the tank recirculation line, passing it through the J-T valve, and then through the heat exchanger, thermal energy is extracted from the bulk liquid and ullage thereby enabling pressure control. The LH2/GHe tests were performed at fill levels of 90%, 50%, and 25% and LN2/GHe tests were conducted at fill levels of 50% and 25%. Moreover, each test was conducted with a specified tank ullage pressure control band. A one-dimensional TVS performance program was used to analyze and correlate the test data. Predictions and comparisons with test data of ullage pressure and temperature and bulk liquid saturation pressure and temperature with test data are presented.

Hedayat, A.↗

NASA NTRS2007

Cryogenic Capillary Screen Heat Entrapment

Cryogenic liquid acquisition devices (LADs) for space-based propulsion interface directly with the feed system, which can be a significant heat leak source. Further, the accumulation of thermal energy within LAD channels can lead to the loss of sub-cooled propellant conditions and result in feed system cavitation during propellant outflow. Therefore, the fundamental question addressed by this program was: "To what degree is natural convection in a cryogenic liquid constrained by the capillary screen meshes envisioned for LADs.?"Testing was first conducted with water as the test fluid, followed by LN2 tests. In either case, the basic experimental approach was to heat the bottom of a cylindrical column of test fluid to establish stratification patterns measured by temperature sensors located above and below a horizontal screen barrier position. Experimentation was performed without barriers, with screens, and with a solid barrier. The two screen meshes tested were those typically used by LAD designers, "200x1400" and "325x2300", both with Twill Dutch Weave. Upon consideration of both the water and LN2 data it was concluded that heat transfer across the screen meshes was dependent upon barrier thermal conductivity and that the capillary screen meshes were impervious to natural convection currents.

Bolshinskiy, L.G.↗