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Ullage

About: Ullage is a research topic. Over the lifetime, 501 publications have been published within this topic receiving 4704 citations. The topic is also known as: headspace.


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Journal ArticleDOI
01 Jan 2017
TL;DR: In this article, the effect of ullage height on steady mass burning rates in methanol pool flames in a cavity was studied and two burner diameters were used to study the effect.
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.

19 citations

Proceedings ArticleDOI
28 Jul 2014
TL;DR: In this paper, the authors present a CFD model for simulating the self-pressurization of a large scale liquid hydrogen storage tank, where the Schrage equation is used to account for the evaporative and condensing interfacial mass flows.
Abstract: This paper presents a CFD (computational fluid dynamics) model for simulating the self-pressurization of a large scale liquid hydrogen storage tank. In this model, the kinetics-based Schrage equation is used to account for the evaporative and condensing interfacial mass flows. Laminar and turbulent approaches to modeling natural convection in the tank and heat and mass transfer at the interface are compared. The flow, temperature, and interfacial mass fluxes predicted by these two approaches during tank self-pressurization are compared against each other. The ullage pressure and vapor temperature evolutions are also compared against experimental data obtained from the MHTB (Multipuprpose Hydrogen Test Bed) self-pressurization experiment. A CFD model for cooling cryogenic storage tanks by spraying cold liquid in the ullage is also presented. The Euler- Lagrange approach is utilized for tracking the spray droplets and for modeling interaction between the droplets and the continuous phase (ullage). The spray model is coupled with the VOF (volume of fluid) 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 predicted by the model are presented. The ullage pressure is compared with experimental data obtained from the MHTB spray bar mixing experiment. The results of the models with only droplet/ullage heat transfer and with heat and mass transfer between the droplets and ullage are compared.

19 citations

Journal ArticleDOI
TL;DR: In this article, the effects of gas-liquid density ratio (DR) near impact zones and in the instants prior to the detection of any compressibility effects are treated and are treated in the current paper.
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.

19 citations

Patent
Edwin E Turner1
07 Jul 1952

19 citations

Journal ArticleDOI
TL;DR: In this paper, a full procedural computational fluid dynamic model was proposed for the jetting, mixing, throttling, and venting processes of thermodynamic venting systems (TVS) for the purpose of minimizing liquid hydrogen boil-off on orbit.

19 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202112
202018
201916
201810
201713
201613