Showing papers on "Ullage published in 2017"

Effect of ullage on burning behavior of small-scale pool fires in a cavity

Abstract: Experiments have been conducted to study the effect of ullage height on steady mass burning rates in methanol pool flames in a cavity. Two burner diameters are used. At low ullages, the flame dynamics are found to be effective in altering the mass burning rates. From baseline case with almost zero ullage, as the ullage is increased, mass burning rate decreases. It produces a local minimum at a given ullage based on the burner internal diameter. After this point, the mass burning rate increases with increasing ullage and reaches an almost uniform value. Numerical simulations are used to complement the results of the experimental study. Low ullage cases have been simulated using a validated numerical model that uses global single step chemistry, partial equilibrium for carbon-dioxide oxidation and optically thin approximation based radiation model. An axisymmetric domain has been employed. Even though the mass burning rates have been over-predicted by the numerical model, the variation trend has been captured quite well. Results from the numerical model reveal that for very low ullage, flame is phenomenally steady and mass burning rate is higher as the diffusion flame anchors around the rim. As the ullage is increased, a transient flame is seen to anchor around the rim and due to increased flame stand-off, the mass burning rate decreases. When the ullage is further increased, due to axial flapping of the flame that partially covers the burner, oxygen is transported into the burner, causing a recirculation pattern within the burner and partial premixing of fuel vapor and oxygen. As a result, the mass burning rate increases.

CFD analysis of aircraft fuel tanks thermal behaviour

Abstract: This work is carried out within the FP7 European research project TOICA (Thermal Overall Integrated Conception of Aircraft, http://www.toica-fp7.eu/). One of the tasks foreseen for the TOICA project is the analysis of fuel tanks as possible heat sinks for future aircrafts. In particular, in the present paper, commercial regional aircraft is considered as case study and CFD analysis with the commercial code STAR-CCM+ is performed in order to identify the potential capability to use fuel stored in the tanks as a heat sink for waste heat dissipated by other systems. The complex physical phenomena that characterize the heat transfer inside liquid fuel, at the fuel-ullage interface and inside the ullage are outlined. Boundary conditions, including the effect of different ground and flight conditions, are implemented in the numerical simulation approach. The analysis is implemented for a portion of aluminium wing fuel tank, including the leading edge effects. Effect of liquid fuel transfer among different tank compartments and the air flow in the ullage is included. According to Fuel Tank Flammability Assessment Method (FTFAM) proposed by the Federal Aviation Administration, the results are exploited in terms of exponential time constants and fuel temperature difference to the ambient for the different cases investigated.

Effects of ullage gas and scale on sloshing loads

Abstract: Gas–liquid density ratio (DR) 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 DR were mainly statistical and effects of DR were usually mixed with those of gas compressibility and ullage gas pressure but attributed only to DR. In an attempt to separately study such effects, Karimi et al. (2015) [11] studied the effects of DR far from impact zones (global effects of gas–liquid density ratio) which proved to be small in the studied range of DR (0.0002 to 0.0060). The effects of DR near impact zones and before detection of any compressibility effects are referred to as local effects and correspond to modifications of wave shape before impact. They were treated in Karimi et al. (2016). This paper studies the influence of ullage gas at the same scale as well as scaling of sloshing loads at different scales. The test setups were similar to those presented in Karimi et al. (2015) [11] and Karimi et al. (2016) and consisted of three 2D model tanks as transverse slices of tank 2 (out of 4) of a membrane LNG carrier with total capacity of 152000 m3 at scales 1:10, 1:20 and 1:40. All model tests were performed at a fill level corresponding to 20% of the tank heights. Water as liquid and 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 DRs from 0.0002 to 0.0060 were used. Synchronized High-speed video cameras (@4000 fps) and arrays of piezo-electric PCB pressure sensors (@40 kHz) monitored and measured impacts on the tank walls. The study was mainly based on the definition of Impact ID based on impact coincidence. The results are presented at 4 main stages. First, in the same way that sloshing loads measured in irregular model tests are treated in the current methodologies, the measured pressure peaks are studied as statistical samples. Next by the notion of impact ID, the effect of change of ullage gas at the same scale is verified. Thirdly with the same notion of impact ID, impacts are tracked down through three scales to verify scaling. At last dominant impact IDs are introduced. It is shown that the most severe impacts are generated by only a few dominant IDs.

Small satellite propulsion system utilizing liquid propellant ullage vapor

Abstract: A novel approach provides a small satellite propulsion system that uses vapor to generate thrust for the small satellite. The vapor naturally sits on top of liquid propellant(s), which are stored within a propellant tank. The vapor may flow from the propellant tank and through a membrane to interact with a reacting surface to generate thrust.

Catalytic inerting system for an aircraft with multiple fuel tanks

Abstract: An example ullage-recirculating catalytic inerting system includes: (i) a plurality of fuel tanks having (a) respective inert gas ports for discharging the inert gas within a respective fuel tank, and (b) respective ullage gas ports for drawing ullage gas from the respective fuel tank; and (ii) an inert gas generating system including (a) an ullage gas inlet port fluidly coupled to the respective ullage gas ports, (b) an inert gas outlet port fluidly coupled to the respective inert gas ports, (c) a catalytic reactor for chemically converting ullage gas received through the ullage gas inlet port to inert gas for discharge through the inert gas outlet port, and (d) a prime mover for moving gas through the inert gas generating system.

Tank System Integrated Model: A Cryogenic Tank Performance Prediction Program

Abstract: Accurate predictions of the thermodynamic state of the cryogenic propellants, pressurization rate, and performance of pressure control techniques in cryogenic tanks are required for development of cryogenic fluid long-duration storage technology and planning for future space exploration missions. This Technical Memorandum (TM) presents the analytical tool, Tank System Integrated Model (TankSIM), which can be used for modeling pressure control and predicting the behavior of cryogenic propellant for long-term storage for future space missions. Utilizing TankSIM, the following processes can be modeled: tank self-pressurization, boiloff, ullage venting, mixing, and condensation on the tank wall. This TM also includes comparisons of TankSIM program predictions with the test data andexamples of multiphase mission calculations.

Low volume nitrogen systems

Abstract: A system to maintain an inert ullage in a hydrocarbon tank. The system provides for outgassing/venting of ullage gases when a high pressure event is found within the tank. Further, when a low pressure event occurs, during fuel discharge or based on ambient conditions, a source of inert gas, such as nitrogen) supplies gas on-demand to the hydrocarbon tank via a pressure regulator (preferably along the venting system) to maintain both the pressure and inerting of the ullage. A method for maintaining the inert ullage is also provided, whereby a low pressure event triggers a supply of inert gas into the tank.