Pressure wave propagation by gas expansion in a high vacuum tube

Takiya, Toshio; Higashino, Fumio; Komura, Akio

doi:10.1116/1.581726

Cited by 11 publications

(5 citation statements)

References 7 publications

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“…The duration of this unsteady region has to be assessed experimentally. It is worth noting that this flow structure is rather similar to that discussed for pulsed beams [29] and for a theory dealing with vacuum leaks [30].…”

Section: Real Flow In An Mgi Delivery Tube and The Ideal Modelsupporting

confidence: 66%

Fuelling efficiency of massive gas injection in TEXTOR: mass scaling and importance of gas flow dynamics

et al. 2011

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Abstract.Fuelling efficiency is an important parameter in designing a massive gas injection system for suppression of runaway electrons in ITER. In this work a Z-dependence of the fuelling efficiency is measured for TEXTOR. The dependence covers the following gases: He, Ne, Ar, Kr, Xe and a 10% Ar-D 2 mixture. It is shown that the fuelling efficiency significantly decreases with the gas mass, from above 0.5 for He to below 0.03 for Xe.To explain the variation of the efficiency with the gas mass and pressure a simple model of the gas flow from the valve to the plasma edge is developed. The flow model is validated by using available laboratory flow measurements of a TEXTOR-similar injection system. The unsteady gas flow and a premature plasma disrupting are shown to explain the mass dependence of the efficiency.

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Section: Real Flow In An Mgi Delivery Tube and The Ideal Modelsupporting

confidence: 66%

Fuelling efficiency of massive gas injection in TEXTOR: mass scaling and importance of gas flow dynamics

et al. 2011

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“…The propagation behavior of the air front must be known in order to arrest the front and restrict the beam-line contamination to a minimal length. Past work on this subject has shown the loss-ofvacuum induced air propagation in a beam-line [2] or in a simple LHe cooled tube [3] to be substantially slower than in a vacuum tube at room temperature [4]. By systematically studying propagation of nitrogen gas (a substitute of air) in high vacuum tubes at different wall temperatures, our previous report [5] identified gas condensation to be a must for this slow propagation.…”

Section: Introductionmentioning

confidence: 99%

Propagation of nitrogen gas in a liquid helium cooled vacuum tube following sudden vacuum loss – Part II: Analysis of the propagation speed

Dhuley

Sciver

2016

International Journal of Heat and Mass Transfer

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The propagation of near-atmospheric nitrogen gas entering a liquid helium (LHe) cooled vacuum tube following an accidental loss of vacuum will be strongly influenced by condensation of the gas on the tube wall. Our previous experimental study revealed that in presence of condensation, the propagation speed of the gas front decreases nearly exponentially as the front advances in the tube. In the present paper the exponential decrease is studied analytically. We reduce the analytical model of the front speed, using assumptions, to show its derivative in the direction of propagation to be proportional to the mass deposition rate near the front. The deposition rate is then calculated at discreet locations along the tube from the condensation heat transfer rate at these locations. We find the deposition rate to diminish nearly exponentially along the tube so that the spatial derivative of the speed will show the same effect. In this special case the front speed will also fall exponentially along the tube. Within the experimental and procedural uncertainty, the exponential decay coefficient of the mass deposition rate also agrees reasonably with the empirically determined exponential decay coefficient of the propagation speed.

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“…When a long channel holding vacuum at room temperature is abruptly opened to atmosphere, the inflowing air will cause a pressure front to propagate down the channel. The front speed in this scenario can be measured by means of an array of pressure probes placed in the channel [1]. The theoretical maximum speed of a gas propagating in a perfect vacuum, called as 'escape speed', is given by 2 / ( 1) a γ − [2].…”

Section: Introductionmentioning

confidence: 99%

Propagation of nitrogen gas in a liquid helium cooled vacuum tube following sudden vacuum loss – Part I: Experimental investigations and analytical modeling

Dhuley

Sciver

2016

International Journal of Heat and Mass Transfer

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This paper describes propagation of near atmospheric nitrogen gas that rushes into a liquid helium (LHe) cooled vacuum tube after the tube suddenly loses vacuum. The loss-of-vacuum scenario resembles accidental venting of atmospheric air to the beam-line of a superconducting particle accelerator and is investigated to understand how the in-flowing air will propagate in such geometry. In controlled experiments, we simulated loss of vacuum by rapidly venting a large reservoir of nitrogen gas (a substitute for air) to a vacuum tube immersed in a LHe bath at 4.2 K. The resulting rise in the tube pressure and temperature were measured by pressure probes and thermometers arranged along the tube length. The data show that the propagation of nitrogen gas in the LHe cooled vacuum tube is orders of magnitude slower than in the same tube at room temperature. Interestingly, the gas front speed in the LHe cooled tube also decreases along the tube. A gas propagation model developed by employing conservation of mass identifies mass transfer (gas condensation in the tube) as the principal cause of the slow propagation as well as of the front deceleration. Some limitations of this analytical model are discussed in the context of quantifying the propagation speed. The speed obtained from direct measurements is seen to decrease exponentially along the tube. This exponential decay form of the propagation speed well represents the data from experiments that have different mass flow rates of nitrogen gas flowing into the vacuum tube after venting.

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Pressure wave propagation by gas expansion in a high vacuum tube

Cited by 11 publications

References 7 publications

Fuelling efficiency of massive gas injection in TEXTOR: mass scaling and importance of gas flow dynamics

Fuelling efficiency of massive gas injection in TEXTOR: mass scaling and importance of gas flow dynamics

Propagation of nitrogen gas in a liquid helium cooled vacuum tube following sudden vacuum loss – Part II: Analysis of the propagation speed

Propagation of nitrogen gas in a liquid helium cooled vacuum tube following sudden vacuum loss – Part I: Experimental investigations and analytical modeling

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