Showing papers on "Ullage published in 2006"

Cryogenic Tank Modeling for the Saturn AS-203 Experiment

Abstract: A computational fluid dynamics (CFD) model is developed for the Saturn S-IVB liquid hydrogen (LH2) tank to simulate the 1966 AS-203 flight experiment. This significant experiment is the only known, adequately-instrumented, low-gravity, cryogenic self pressurization test that is well suited for CFD model validation. A 4000-cell, axisymmetric model predicts motion of the LH2 surface including boil-off and thermal stratification in the liquid and gas phases. The model is based on a modified version of the commercially available FLOW3D software. During the experiment, heat enters the LH2 tank through the tank forward dome, side wall, aft dome, and common bulkhead. In both model and test the liquid and gases thermally stratify in the low-gravity natural convection environment. LH2 boils at the free surface which in turn increases the pressure within the tank during the 5360 second experiment. The Saturn S-IVB tank model is shown to accurately simulate the self pressurization and thermal stratification in the 1966 AS-203 test. The average predicted pressurization rate is within 4% of the pressure rise rate suggested by test data. Ullage temperature results are also in good agreement with the test where the model predicts an ullage temperature rise rate within 6% of the measured data. The model is based on first principles only and includes no adjustments to bring the predictions closer to the test data. Although quantitative model validation is achieved or one specific case, a significant step is taken towards demonstrating general use of CFD for low-gravity cryogenic fluid modeling.

Oxygen removal system

Abstract: A system and process to deplete or remove oxygen in the ullage of a fuel tank to reduce the oxygen/fuel vapor ratio below a lower explosion limit by exposing the ullage compounds to an oxygen removal catalyst active at a relatively low temperature. The oxygen removal catalyst may be a non-precious metal catalyst. A selective reaction of the oxygen by the catalyst forms primarily alcohols, aldehydes, and/or ketones and produces less than about 5% water by volume. The selective reaction, occurring at the relatively low temperature, reduces the risk of flammability of the fuel.

Testing of a Spray‐Bar Thermodynamic Vent System in Liquid Nitrogen

Abstract: To support development of a microgravity pressure control capability for liquid oxygen (LO2), Thermodynamic Vent System (TVS) testing was conducted at Marshall Space Flight Center (MSFC) using liquid nitrogen (LN2) as an LO2 simulant. The spray‐bar TVS hardware used was originally designed by The Boeing Company for testing in liquid hydrogen (LH2). With this concept, a small portion of the tank fluid is passed through a Joule‐Thomson (J‐T) device, and then through a longitudinal spray‐bar mixer/heat exchanger in order to cool the bulk fluid. To accommodate the larger mass flow rates associated with LN2, the TVS hardware was modified by replacing the recirculation pump with an LN2 compatible pump and replacing the J‐T valve. The primary advantage of the spray‐bar configuration is that tank pressure control can be achieved independent of liquid and vapor location, enhancing the applicability of ground test data to microgravity conditions. Performance testing revealed that the spray‐bar TVS was effective in controlling tank pressure within a 6.8‐kPa band for fill levels of approximately 90%, 50%, and 25%. Tests were also conducted with gaseous helium (GHe) in the ullage. The TVS operated satisfactorily with GHe in the ullage. However, the total cycle duration increase ranged from 14% to 28% compared to similar tests with gaseous nitrogen (GN2). Testing demonstrated that the spray‐bar TVS design was flexible enough for use in two different propellants with minimal hardware modifications.

Systems and methods for refueling spacecraft

Abstract: Systems and methods for refueling spacecraft are disclosed herein. In one embodiment, a method for transferring propellant from a first spacecraft to a second spacecraft includes releasably connecting a first propellant conduit carried by the first spacecraft to a second propellant conduit carried by the second spacecraft, and releasably connecting a first ullage conduit carried by the first spacecraft to a second ullage conduit carried by the second spacecraft. The method can further include transferring propellant from a first propellant tank carried by the first spacecraft to a second propellant tank carried by the second spacecraft via the first and second propellant conduits. As the propellant is flowing from the first propellant tank to the second propellant tank, the method can additionally include transferring ullage from the second propellant tank to the first propellant tank via the first and second ullage conduits.

Liquid Nitrogen (Oxygen Simulant) Thermodynamic Vent System Test Data Analysis

Abstract: In designing systems for the long‐term storage of cryogens in low‐gravity (space) environments, one must consider the effects of thermal stratification on tank pressure that will occur due to environmental heat leaks During low‐gravity operations, a Thermodynamic Vent System (TVS) concept is expected to maintain tank pressure without propellant resettling A series of TVS tests was conducted at NASA Marshall Space Flight Center (MSFC) using liquid nitrogen (LN2) as a liquid oxygen (LO2) simulant The tests were performed at tank fill levels of 90%, 50%, and 25%, and with a specified tank pressure control band A transient one‐dimensional TVS performance program is used to analyze and correlate the test data for all three fill levels Predictions and comparisons of ullage pressure and temperature and bulk liquid saturation pressure and temperature with test data are presented

Liquid measurement system with differential pressure probes

Abstract: The weight of liquid in a tank subject to tilting is determined by measuring differences in air pressure in the ullage (the empty volume of the tank above the level of the liquid) and the air pressure produced by the weight of the liquid at the bottom of the tank. The pressures at the bottom of the tank are measured in a plurality of locations, and the differential pressures are combined to compensate for changes in the depth of the liquid when the tank is not level (e.g., when the tank is in an aircraft flying at an attitude other than straight and level). The electronics to measure the pressure and to process the pressure measurements are located remotely form the tanks, thus eliminating the possibility of ignition caused by the electronics when the liquid is fuel or other flammable liquid.

System and Method for Storing Cryogenic Liquid Air

Abstract: An apparatus for storing liquid air (a cryogenic mixture of about 80% liquid nitrogen and about 20% liquid oxygen) in a stable condition within a storage vessel routes colder liquid nitrogen from an external source, through a condensing coil/heat exchanger that passes through the ullage space of the vessel. This will result in condensing the nitrogen-rich vapor into the mass as a liquid, thereby reducing ullage pressure, cooling the mass, and ultimately precluding oxygen-enrichment through boil-off.

Ormosil coating-based oxygen sensor for aircraft ullage

Abstract: Significant emphasis has been placed on fuel tank safety since the TWA flight 800 accident in July 1996. Upon investigation the National Transportation Safety Board (NTSB) determined that the probable cause of the accident was an explosion of the center wing tank (CWT), resulting from ignition of the flammable fuel/air mixture in the tank. The Federal Aviation Administration (FAA) has focused research to support two primary methods of fuel tank protection -- ground-based and on-board -- both involving fuel tank inerting. Ground-based fuel tank inerting involves some combination of fuel scrubbing and ullage washing with Nitrogen Enriched Air (NEA) while the airplane is on the ground (applicable to all or most operating transport airplanes). On-board fuel tank inerting involves ullage washing with OBIGGS (on-board inert gas generating system), a system that generates NEA during aircraft operations. An OBIGGS generally encompasses an air separation module (ASM) to generate NEA, a compressor, storage tanks, and a distribution system. Essential to the utilization of OBIGGS is an oxygen sensor that can operate inside the aircraft's ullage and assess the effectiveness of the inerting systems. OBIGGS can function economically by precisely knowing when to start and when to stop. Toward achieving these goals, InnoSense LLC is developing an all-optical fuel tank ullage sensor (FTUS) prototype for detecting oxygen in the ullage of an aircraft fuel tank in flight conditions. Data would be presented to show response time and wide dynamic range of the sensor in simulated flight conditions and fuel tank environment.

Experimental and Computational Studies of Jet Fuel Flow near the Freeze Point

Abstract: To study the flow behavior of jet fuel at low temperatures, a wing-tank thermal simulator, which represents the fuel tank of a commercial aircraft, was fabricated. The simulator was subjected to cooling in an environmental chamber. Experimental results show that fuel flowability and pumpability decrease substantially as temperature is reduced. Time-dependent temperature and velocity distributions were numerically simulated for static cooling. Viscosities were obtained from viscometer measurements using different jet fuel samples. It was observed that near the freeze-point temperature, low freeze-point fuels tend to have higher viscosities than high freeze-point fuels. Measured viscosities were used in computational-fluid-dynamics simulations of jet fuel that was cooled. The calculations show that stringers, ribs, and other structures strongly promote fuel cooling. Also, the cooler, denser fuel resides near the bottom surface of the fuel tank simulator. The presence of an ullage space within the tank was found to strongly influence the fuel temperature profile by sometimes reducing cooling from the upper surface. In other instances, the ullage space enhanced cooling.

Studying Flammability in a Commercial Transport Fuel Tank with Inerting

Abstract: As part of the continued emphasis on fuel tank safety, the Federal Aviation Administration (FAA) has developed a demonstration fuel tank inerting system and has tested it on a NASA -operated Boeing 747 aircraft. To support this, the FAA developed two models to predict both fuel tank oxygen concentration and flammability in an inerted ullage, based on pre viously developed models and calculations. Laboratory and aircraft test results indicated that the models duplicated measured data trends well and gave predicted peak values with a reasonable degree of accuracy. This allowed the FAA to develop a repr esentative Boeing 747 aircraft flight cycle and give predictions of flammability exposure for the given ullage. The results indicated that the aircraft fuel tank would not be exposed to flammable conditions during the developed flight profile with the represented inerting system even though part of the tank ullage did achieve oxygen concentration levels of approximately 18%.