Showing papers on "Ullage published in 2015"

Effect of ullage gas on sloshing, Part II: Local effects of gas–liquid density ratio

Abstract: Gas–liquid density ratio ( D R ) is a key dimensionless number in sloshing assessment methodologies of membrane containment systems for LNG tanks of floating structures. Earlier studies on the effect of D R were mainly statistical and effects of D R were usually mixed with those of gas compressibility and ullage gas pressure but attributed only to D R . In an attempt to separately study such effects, part I of this work studied the effects of D R far from impact zones (global effects of gas–liquid density ratio) which proved to be small in the studied range of D R (0.0002 to 0.0060). The effects of D R near impact zones and in the instants prior to the detection of any compressibility effects are referred to as local effects and are treated in the current paper (part II). The test setup was identical to the one presented in Part I and consisted of two 2D model tanks representing transverse slices of tank 2 (out of 4) of a membrane LNG carrier with total capacity of 152000 m3 at scales 1:20 and 1:40. Both model tests were performed at 20% fill level of the tank heights. Water was the main liquid that was used. In some tests at scale 1:20 a solution of sodium polytungstate (SPT) was also used which had a higher density compared to water. Different ullage gases of helium (He), air, two mixtures of sulfur hexafluoride (SF6) and nitrogen (N2), and pure SF6, all at atmospheric pressure with a range of D R s from 0.0002 to 0.0060 were utilized. Synchronized high-speed video cameras (@4000 fps) and arrays of piezo-electric PCB (112A21 and 112M361) pressure sensors (@40 kHz) monitored and measured impacts on the tank walls. In Part II of the study short and more regular tank motions which generated highly repeatable single impact waves (SIW) were used instead of long irregular tank motions which were considered in part I. By comparing the single impact waves (SIW) generated by identical tank motions but with different D R s, it was observed that D R clearly modifies wave shapes prior to the moment of wave breaking. Larger D R s tend to slow down the wave front and delay breaking. It was also observed that larger D R s slightly slow down wave trough runup as well. Those effects would also lead to a mild shift of impact types by changing the D R (for example Flip-through to slosh or large gas-pocket to small gas-pocket impacts). By comparing single impact waves (SIW) generated by identical tank motions and the same D R but with different gas and liquid densities it was shown that keeping the same D R is essentially needed to keep the same impact geometry as recommended by the existing sloshing assessment methodologies. Free surface instabilities were also very similar for those waves generated with the same tank motions and similar DR but with different gases and liquids. Considering the reduction of wave kinetic energy by heavier 1 ullage gases as a relevant source of the statistical reduction of impact pressures and having in mind the mild shift of wave impact types caused by the change of D R it is still to be studied further why the heavier gas leads to smaller statistical pressures.

CFD Modeling of the Multipurpose Hydrogen Test Bed (MHTB) Self-Pressurization and Spray Bar Mixing Experiments in Normal Gravity: Effect of the Accommodation Coefficient on the Tank Pressure

Abstract: A CFD model for simulating the self-pressurization of a large scale liquid hydrogen storage tank is utilized in this paper to model the MHTB self-pressurization experiment. The kinetics-based Schrage equation is used to account for the evaporative and condensi ng interfacial mass flows in this model. The effect of the accommodation coefficient for calculating the interfacial mass transfer rate on the tank pressure during tank selfpressurization is studied. The values of the accommodation coefficient which were considered in this study vary from 1.0e-3 to 1.0e-1 for the explicit VOF model and from 1.0e-4 to 1.0e-3 for the implicit VOF model. The ullage pressure evolutions are compared against experimental data. A CFD model for controlling pressure in cryogenic storage tanks by spraying cold liquid into the ullage is also presented. The Euler-Lagrange approach is utilized for tracking the spray droplets and for modeling the interaction between the droplets and the continuous phase (ullage). The spray model is coupled with the VOF model by performing particle tracking in the ullage, removing particles from the ullage when they reach the interface, and then adding their contributions to the liquid. Droplet-ullage heat and mass transfer are modeled. The flow, temperature, and interfacial mass flux, as well as droplets trajectories, size distribution and temperatures predicted by the model are presented. The ul lage pressure and vapor temperature evolutions are compared with experimental data obtained from the MHTB spray bar mixing experiment. The effect of the accommodation coefficient for calculating the interfacial and droplet mass transfer rates on the tank pressure during mixing of the vapor using spray is studied. The values used for the accommodation coefficient at the interface vary from 1.0e-5 to 1.0e-2. The droplet accommodation coefficient values vary from 2.0e-6 to 1.0e-4.

Aircraft fuel system

Abstract: The invention provides an aircraft fuel system comprising a fuel storage facility for storing fuel and ullage, a separate ullage storage facility for storing ullage, and a transfer arrangement for transferring ullage between the fuel storage facility and the ullage storage facility, wherein the transfer arrangement is capable of controlling the transfer of ullage based on a pressure input to the transfer arrangement. The invention also provides an aircraft with such a fuel system and a method of operating an aircraft.

Device and method for measuring ullage and material level of mine deep-hole chute

Abstract: The invention discloses a device and a method for measuring the ullage and the material level of a mine deep-hole chute and aims at solving the technical problem of accurate online continuous material level measurement when the mine deep-hole chute is blocked by high-concentration dust. The device for measuring the ullage and the material level of the mine deep-hole chute comprises a chute measuring trolley, a laser level meter, an electric rocker arm, a digital display instrument, a PLC and a video sighting system, wherein the electric rocker arm is fixedly connected to the chute measuring trolley; the video sighting system comprises a camera and a liquid crystal monitor; the camera is located on the front end of the electric rocker arm, while the liquid monitor is located on the rear end of the electric rocker arm; the camera is connected with the liquid crystal monitor by use of a transmission cable; the laser level meter is connected with the input end of the PLC; the output end of the PLC is connected with the input end of the digital display instrument. The device for measuring the ullage and the material level of the mine deep-hole chute is integrated with the high-accuracy laser level meter and the auxiliary devices, and is used for measuring by use of a soft measurement method, and the overall measurement accuracy can be +/-1%FS.

Parametric Visualization Study of Self-Pressurizing Propellant Tank Dynamics

Abstract: Nitrous oxide is frequently used as a self-pressurizing propellant in hybrid rocket propulsion systems. To study the behavior of these self-pressurized propellant tanks, two different pressure vessels with optical access have been developed that can be filled with nitrous oxide and drained in a way that replicates the conditions of a hybrid rocket motor firing. Carbon dioxide was used as a simulant fluid for nitrous oxide to mitigate explosion and environmental hazards. High speed cameras are used to visualize the internal flow and identify boiling, condensation, and liquid level motion while pressure and temperature sensors are used to determine the thermodynamic state within the tank. Tests have identified two separate temporal regimes that are common to all tests, a transient and steady state, each described by distinct features. The transient regime is characterized by a rapid pressure drop and recovery, with homogeneous condensation of the ullage and heterogeneous nucleation and growth of bubbles in the liquid. The steady state regime begins when a large population of bubbles has been formed in the liquid and a balance is established between nucleation of new bubbles and death of bubbles as they reach the free surface and transfer their mass to the ullage. During this steady state regime the liquid and vapor are both homogeneous two-phase mixtures and the pressure drops in a linear fashion as the liquid drains from the tank. Also presented in this paper are the results of tests of parameter variations, including flow rate, fill level, temperature, initial bubble population, and scaling effects. The same basic features are present in each of these tests.

Aircraft fuel system

Abstract: The invention provides an aircraft fuel system comprising a fuel storage facility 51 for storing fuel and ullage, a separate ullage storage facility 62 for storing ullage, and a transfer arrangement 56, 61 for transferring ullage between the fuel storage facility and the ullage storage facility, wherein the transfer arrangement is capable of controlling the transfer of ullage 57 based on a pressure input to the transfer arrangement The invention also provides an aircraft 10 with such a fuel system and a method of operating an aircraft 10

Liquid Hydrogen Propellant Tank Sub-Surface Pressurization with Gaseous Helium

Abstract: A series of tests were conducted to evaluate the performance of a propellant tank pressurization system with the pressurant diffuser intentionally submerged beneath the surface of the liquid. Propellant tanks and pressurization systems are typically designed with the diffuser positioned to apply pressurant gas directly into the tank ullage space when the liquid propellant is settled. Space vehicles, and potentially propellant depots, may need to conduct tank pressurization operations in micro‐gravity environments where the exact location of the liquid relative to the diffuser is not well understood. If the diffuser is positioned to supply pressurant gas directly to the tank ullage space when the propellant is settled, then it may become partially or completely submerged when the liquid becomes unsettled in a microgravity environment. In such case, the pressurization system performance will be adversely affected requiring additional pressurant mass and longer pressurization times. This series of tests compares and evaluates pressurization system performance using the conventional method of supplying pressurant gas directly to the propellant tank ullage, and then supplying pressurant gas beneath the liquid surface. The pressurization tests were conducted on the Engineering Development Unit (EDU) located at Test Stand 300 at NASA Marshall Space Flight Center (MSFC). EDU is a ground based Cryogenic Fluid Management (CFM) test article supported by Glenn Research Center (GRC) and MSFC. A 150 ft3 propellant tank was filled with liquid hydrogen (LH2). The pressurization system used regulated ambient helium (GHe) as a pressurant, a variable position valve to maintain flow rate, and two identical independent pressurant diffusers. The ullage diffuser was located in the forward end of the tank and was completely exposed to the tank ullage. The submerged diffuser was located in the aft end of the tank and was completely submerged when the tank liquid level was 10% or greater. The ullage diffuser tests were conducted as a baseline to evaluate the performance of the pressurization system, and the submerged diffuser tests showed how the performance of the pressurization system was compromised when the diffuser was submerged in LH2. The test results are evaluated and compared, and included in this report for various propellant tank fill levels.

Simscape Modeling of a Custom Closed-Volume Tank

Abstract: The library for Mathworks Simscape does not currently contain a model for a closed volume fluid tank where the ullage pressure is variable. In order to model a closed-volume variable ullage pressure tank, it was necessary to consider at least two separate cases: a vertical cylinder, and a sphere. Using library components, it was possible to construct a rough model for the cylindrical tank. It was not possible to construct a model for a spherical tank, using library components, due to the variable area. It was decided that, for these cases, it would be preferable to create a custom library component to represent each case, using the Simscape language. Once completed, the components were added to models, where filling and draining the tanks could be simulated. When the models were performing as expected, it was necessary to generate code from the models and run them in Trick (a real-time simulation program). The data output from Trick was then compared to the output from Simscape and found to be within acceptable limits.

Liquid Acquisition Device Hydrogen Outflow Testing on the Cryogenic Propellant Storage and Transfer Engineering Design Unit

Abstract: As part of the NASA Cryogenic Propellant Storage and Transfer (CPST) Engineering Design Unit (EDU) testing with liquid hydrogen, screen-channel liquid acquisition devices (LADs) were tested during liquid hydrogen outflow from the EDU tank. A stainless steel screen mesh (325x2300 Dutch T will weave) was welded to a rectangular cross-section channel to form the basic LAD channel. Three LAD channels were tested, each having unique variations in the basic design. The LADs fed a common outflow sump at the aft end of the 151 cu. ft. volume aluminum tank, and included a curved section along the aft end and a straight section along the barrel section of the tank. Wet-dry sensors were mounted inside the LAD channels to detect when vapor was ingested into the LADs during outflow. The use of warm helium pressurant during liquid hydrogen outflow, supplied through a diffuser at the top of the tank, always led to early breakdown of the liquid column. When the tank was pressurized through an aft diffuser, resulting in cold helium in the ullage, LAD column hold-times as long as 60 minutes were achieved, which was the longest duration tested. The highest liquid column height at breakdown was 58 cm, which is 23 less than the isothermal bubble-point model value of 75 cm. This paper discusses details of the design, construction, operation and analysis of LAD test data from the CPST EDU liquid hydrogen test.

Method, Apparatus and Composition for a Payload Delivery System for Delivery of Radioactive High Level Waste Payloads to Sun Storage

Abstract: A method, apparatus and composition are described for a payload delivery system capable of moving a radioactive high level waste payload from the Earth to being captured by the Sun. The payload delivery system comprises a rocket system capable of being carried and launched from an aircraft. The rocket system has at least one stage that utilizes one and only one propellant being a single liquid propellant and a final stage that utilizes pneumatic cannon driven by the final stage combustion or ullage gases to propel the radioactive high level waste payload toward the Sun.