Introduction to Molecular Beams Gas Dynamics

Sanna, Giovanni; Tomassetti, Giuseppe

doi:10.1142/p387

Cited by 52 publications

(40 citation statements)

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“…With the measured densities, n m , a total of N 1 linear algebraic equations about 1 -5 , are properly constructed; Step 7: for each of the N 2 measured number fluxes along the X-direction, (nU) m , by using the θ 1 and θ 2 for each point, and the seven guessed parameters, n 0g , S 0g , n bg , S bg , α 0g , T 0g and T bg , a set of coefficients B 1 -B 7 can be computed, and a guessed jet number flux (nU) jg can also be computed by using Equation (3). A total of N 2 linear algebraic equations about 1 -7 are properly constructed; Step 8: for each of the N 3 measured number fluxes along the Y-direction, (nV) m , by using the θ 1 and θ 2 , and the seven guessed parameters, n 0g , S 0g , n bg , S bg , α 0g , T 0g and T bg , seven coefficients C 1 -C 7 can be computed.…”

Section: Linearized Governing Equations For the Density And Number Flmentioning

confidence: 99%

“…For many engineering applications under near vacuum conditions, such as molecular beams [1], materials processing inside vacuum chambers [2], and electric propulsion (EP) devices in a space environment [3], there are always dilute background flows. For plume investigations, which are important to the rocket industry, the cosine law model [4] is a good example for modeling the background flow effects.…”

Section: Introductionmentioning

confidence: 99%

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A New Gaskinetic Model to Analyze Background Flow Effects on Weak Gaseous Jet Flows from Electric Propulsion Devices

Cai

2017

Aerospace

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Recent work on studying rarefied background and jet flow interactions is reported. A new gaskinetic method is developed to investigate two closely related problems. The first problem is how a collisionless background flow can affect a highly rarefied jet flow. The rarefied jet and background flow conditions are assumed available and described with seven parameters. Gaskinetic theories are applied and formulas are obtained for the mixture properties. Simulations are performed to validate these expressions, and excellent agreement is obtained. The second problem is to recover the collisionless background and jet flow parameters with limited measurements. A group of linearized equations are derived for the flowfield properties. The solving process includes initial estimations on the seven parameters, followed with iterations. Numerical tests are performed and the results indicate the procedure is accurate and efficient. The new method and expressions can reduce the amount of experimental work and numerical simulations to analyze facility effects. Parameter studies with particle simulations may require several months; however, the new methods may require minutes. These methods can be used to quantify and predict jet performance, vacuum chamber designs and optimization. Applications may be for many societies using vacuum conditions.

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Section: Linearized Governing Equations For the Density And Number Flmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A New Gaskinetic Model to Analyze Background Flow Effects on Weak Gaseous Jet Flows from Electric Propulsion Devices

Cai

2017

Aerospace

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“…In other words, due to the more ordered velocity distribution established by the stagnation temperature inside the BGC cell, conversion into forward velocity of the beam will occur to a much lower extent. A quantitative treatment starts with the Bernoulli equation describing a stationary, adiabatic and irrotational flow of a compressible fluid in the absence of gravity, viscosity and shock waves [32]. Written in differential form for a fluid unit mass, this reads as u du + dp…”

Section: Further Reduction Of the Beam Temperaturementioning

confidence: 99%

Assessing the time constancy of the proton-to-electron mass ratio by precision ro-vibrational spectroscopy of a cold molecular beam

Amato

Sarno

Ricciardi

et al. 2014

Journal of Molecular Spectroscopy

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We report the design of an experiment that aims to constrain, over a-fewyear timescale, the fractional temporal variation of the proton-to-electron mass ratio, β = m p /m e , at a level of 10 −15 /yr by means of a spectroscopic frequency measurement on a beam of cold CF 3 H molecules. This is extracted from a buffer-gas-cooling source and then collimated by means of an electrostatic hexapole lens. Employed in a two-photon Ramsey-fringes interrogation scheme, the probe source is based on a mid-infrared quantum cascade laser, phase-locked to a specially-developed optical frequency comb that is ultimately referenced to the Cs primary standard via an optical fiber link.

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“…The Kn number is usually defined as Kn = λ/L, where λ is the molecule mean free path and L is a characteristic length. Several examples include atomic/molecular beams [7,8], materials processing inside vacuum chambers [9], rocket plume effects on spacecraft solar panels [10], and lunar landing vehicles and missions [11][12][13][14][15][16]. In fact, if the exit speed is high relative to the mean thermal speed, molecules leaving the nozzle exit quickly, barely having time for collisions.…”

Section: Introductionmentioning

confidence: 99%

Gaskinetic Modeling on Dilute Gaseous Plume Impingement Flows

Cai¹

2016

Aerospace

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This paper briefly reviews recent work on gaseous plume impingement flows. As the major part of this paper, also included are new comprehensive studies on high-speed, collisionless, gaseous, circular jet impinging on a three-dimensional, inclined, diffuse or specular flat plate. Gaskinetic theories are adopted to study the problems, and several crucial geometry-location and velocity-direction relations are used. The final complete results include impingement surface properties such as pressure, shear stress, and heat flux. From these surface properties, averaged coefficients of pressure, friction, heat flux, moment over the entire flat plate, and the distance from the moment center to the flat plate center are obtained. The final results include accurate integrations involving the geometry and specific speed ratios, inclination angle, and the temperature ratio. Several numerical simulations with the direct simulation Monte Carlo method validate these analytical results, and the results are essentially identical. The gaskinetic method and processes are heuristic and can be used to investigate other external high Knudsen (Kn) number impingement flow problems, including the flow field and surface properties for a high Knudsen number jet from an exit and flat plate of arbitrary shapes. The results are expected to find many engineering applications, especially in aerospace and space engineering.

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Introduction to Molecular Beams Gas Dynamics

Cited by 52 publications

References 0 publications

A New Gaskinetic Model to Analyze Background Flow Effects on Weak Gaseous Jet Flows from Electric Propulsion Devices

A New Gaskinetic Model to Analyze Background Flow Effects on Weak Gaseous Jet Flows from Electric Propulsion Devices

Assessing the time constancy of the proton-to-electron mass ratio by precision ro-vibrational spectroscopy of a cold molecular beam

Gaskinetic Modeling on Dilute Gaseous Plume Impingement Flows

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