Translational freezing in free jet expansions, with special reference to molecular beam formation

1969 ◽  
Vol 47 (12) ◽  
pp. 2161-2165 ◽  
Author(s):  
Rodney L. LeRoy ◽  
Jacques M. Deckers
Keyword(s):  
Distribution Function ◽  
Transition Region ◽  
Molecular Beam ◽  
Collision Frequency ◽  
Collision Cross Section ◽  
Experimental Studies ◽  
Velocity Distribution Function ◽  
Free Jet ◽  
Beam Formation ◽  
Good Agreement

A theoretical model is described which can be used to calculate the velocity distribution function in the transition region of a free jet expansion. It makes use of a simple mechanism to account for the way in which collisions "perturb" the distribution function which would apply in the absence of collisions. The results are compared with experimental studies of argon beams isolated from free jet sources. If the collision frequency is calculated using a hard sphere collision cross section of (25 ± 5) Å2, good agreement with experimental beam intensity profiles is obtained. In the transition region computed values of the bulk mass velocity, and of the parallel and perpendicular temperatures, are intermediate between the values which would be found if the flow were collision-dominated or free molecular. In particular the perpendicular temperature varies slowly from a dependence on the −4/3 power of the distance from the source, approaching monotonically a −2 power dependence at large distances.

Constant frequency oscillations in a bounded thermally produced plasma

1971 ◽  
Vol 322 (1548) ◽  
pp. 63-72 ◽  
Keyword(s):  
Distribution Function ◽  
Thermal Plasma ◽  
Velocity Distribution Function ◽  
Frequency Oscillation ◽  
Constant Frequency ◽  
Free Theory ◽  
Ion Velocity Distribution Function ◽  
A Current ◽  
Theory And Experiment ◽  
Good Agreement

Measurements are reported of a constant frequency oscillation in a current-carrying thermal plasma. A collision-free theory is presented which includes a standing wave in the plasma together with a sheath oscillation. It is postulated that the ion velocity distribution function becomes flattened at v =±ω/k and this gives good agreement between theory and experiment.

scholarly journals Effect of Proximity to Bed on 30° and 45° Inclined Dense Jets: A Numerical Study

2021 ◽  
Author(s):  
Mohammadmehdi Ramezani ◽  
Ozeair Abessi ◽  
Ali Rahmani Firoozjaee
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Lower Boundary ◽  
Geometrical Properties ◽  
Free Jet ◽  
Rise Height ◽  
Desalination Plants ◽  
Inclined Dense Jets ◽  
Good Agreement ◽  
Return Point

Abstract Employing inclined dense jets is a common way for the disposal of brine effluent from coastal desalination plants. This paper numerically analyzes the mixing and geometrical properties of 30° and 45° inclined dense jets when they discharge close to the bed. For this purpose, two series of numerical simulations were developed. First, the nozzle acts as a free jet when it is placed far enough from the lower boundary. Meanwhile, in the second series, the distance between the nozzle tip and seabed is substantially reduced. Consequently, by comparing these two series, the effect of proximity to bed on the behavior of dense jets is investigated. The governing equations are solved by modifying a solver within the CFD package of OpenFOAM. The numerical results are presented in comparative figures and compared to the previous works. Comparisons indicated that the numerical model predicts the geometrical characteristics of dense jets in good agreement with the past experimental studies. However, the dilution predictions are conservative. It has been observed that proximity to the bed has almost no appreciable effects on the behavior of 45° jets. However, for 30° jets, when the bed proximity parameter ( Y0/LM ) falls below 0.14, normalized values of horizontal and vertical locations of centerline peak and return point dilution are slightly reduced while the terminal rise height remains untouched.

scholarly journals Experimental studies of supercavitating flow about simple two-dimensional bodies in a jet

1959 ◽  
Vol 5 (3) ◽  
pp. 337-354 ◽  
Author(s):  
Edward Silberman
Keyword(s):  
Linear Theory ◽  
Experimental Studies ◽  
Cavitation Number ◽  
Two Dimensional ◽  
University Of Minnesota ◽  
Flat Plates ◽  
Force Coefficients ◽  
Free Jet ◽  
Fluid Theory ◽  
Good Agreement

A two-dimensional free-jet water tunnel developed at the St Anthony Falls Hydraulic Laboratory of the University of Minnesota is described briefly. Results of experimental measurements on a two-dimensional cup, symmetrical wedges, inclined flat plates, and a circular cylinder in the tunnel are given.Measured force coefficients at zero cavitation number are in good agreement with theory. Shapes of the cavities were computed for one of the wedges and for one of the plates at zero cavitation number; the observed shapes are also in good agreement with the theory.For non-zero cavitation numbers, theoretical results for force coefficients were available for comparison in only two cases. For one of these, the cup, agreement between theory and experiment was good up to a cavitation number of about 0.5. For the other, a symmetrical wedge, experimental results were compared with a linear theory with good agreement for cavitation numbers between about 0.1 and 0.3. In the case of the wedge, measured cavity lengths were somewhat shorter than predicted by the linear theory. All other comparisons with theory at non-zero cavitation number had to be made with the theory as developed for infinite fluid. The experimental force coefficients were less than predicted by infinite-fluid theory, but tended to approach the theoretical values as the cavitation number increased. A similar tendency marked the comparison between the experimental data and data taken by others in closed tunnels.

Propagation of a Strong Circularly Polarized Electromagnetic Wave through Afterglow Plasmas near the Electron Cyclotron Frequency

1971 ◽  
Vol 49 (22) ◽  
pp. 2797-2824 ◽  
Author(s):  
I. P. Shkarofsky
Keyword(s):  
Distribution Function ◽  
Electric Field ◽  
Electron Density ◽  
Cyclotron Resonance ◽  
Collision Frequency ◽  
Strong Field ◽  
Velocity Distribution Function ◽  
Decay Rates ◽  
Relaxation Processes ◽  
Experimental Conditions

We seek to explain the experimental observation of enhanced transmission of a strong right-hand circular wave near cyclotron resonance in an afterglow helium slab plasma occurring at earlier times than for a corresponding weak electromagnetic field. A strong field heats the electrons and alters the collision frequency and the velocity distribution function. For our experimental conditions, electron–electron relaxation processes can influence the distribution function. Furthermore, because of the field dependent absorption coefficient, the temperature and field strength can vary within the plasma slab. Although the collision frequency increase with temperature predicts an earlier time for stronger-field transmission at cyclotron resonance, none of the above processes is sufficient to explain the experimentally observed large spread in times of transmission for various electric field strengths. The explanation is ascribed to the fact that the electron density decay constant due to diffusion also increases with temperature, so that the electron density decay rates vary with electric field resulting in a larger spread in times of transmission. Experimental results from double probes, although operating under low sensitivity, suggest a decrease in density near the front edge of the plasma subject to strong fields.

Plane simple shear of smooth inelastic circular disks: the anisotropy of the second moment in the dilute and dense limits

1988 ◽  
Vol 192 ◽  
pp. 313-328 ◽  
Author(s):  
J. T. Jenkins ◽  
M. W. Richman
Keyword(s):  
Distribution Function ◽  
Simple Shear ◽  
Velocity Distribution Function ◽  
Analytic Solutions ◽  
Qualitative Behaviour ◽  
Velocity Fluctuations ◽  
Second Moment ◽  
Dense Flows ◽  
Circular Disks ◽  
Good Agreement

We consider a plane, steady, homogeneous flow of circular disks. The disks are identical, smooth, and inelastic. We adopt the assumption of molecular chaos and introduce an anisotropic Maxwellian velocity distribution function based on the full second moment of the velocity fluctuations. In the limits of dilute and dense flows, we determine approximate analytic solutions of the balance law for the second moment that result in stresses whose qualitative behaviour and magnitudes are in good agreement with numerical simulations.

Thermal flux reduction by electromagnetic instabilities

1978 ◽  
Vol 20 (3) ◽  
pp. 405-417 ◽  
Author(s):  
Toshio Okada ◽  
Takashi Yabe ◽  
Keishiro Niu
Keyword(s):  
Distribution Function ◽  
Thermal Conduction ◽  
Linear Growth ◽  
Thermal Flux ◽  
Velocity Distribution Function ◽  
Electron Plasma ◽  
High Energy ◽  
Particle In Cell ◽  
High Energy Tail ◽  
Good Agreement

From a dispersion relation, linear growth rates of electromagnetic instabilities are obtained in an electron plasma whose velocity distribution function has a high-energy tail. Theory is developed to derive the reduction in the thermal flux caused by these electromagnetic instabilities. Nonlinear theory leads to the saturation level of instabilities. Numerical simulations are carried out using a particle-in-cell method. The reduction in thermal conduction predicted by the theory is found to be in good agreement with computer simulations.

scholarly journals Experimental studies on the transformation from firn to ice in the wet-snow zone of temperate glaciers

1997 ◽  
Vol 24 ◽  
pp. 181-185 ◽  
Author(s):  
Katsuhisa Kawashima ◽  
Tomomi Yamada
Keyword(s):  
Experimental Studies ◽  
Ice Formation ◽  
Compression Tests ◽  
Densification Rate ◽  
Overburden Pressure ◽  
Proportionality Constant ◽  
Wet Snow ◽  
Water Saturated ◽  
The Relationship ◽  
Good Agreement

The densification of water-saturated firn, which had formed just above the firn-ice transition in the wet-snow zone of temperate glaciers, was investigated by compression tests under pressures ranging from 0.036 to 0.173 MPa, with special reference to the relationship between densification rate, time and pressure. At each test, the logarithm of the densification rate was proportional to the logarithm of the time, and its proportionality constant increased exponentially with increasing pressure. The time necessary for ice formation in the firn aquifer was calculated using the empirical formula obtained from the tests. Consequently, the necessary time decreased exponentially as the pressure increased, which shows that the transformation from firn in ice can be completed within the period when the firn aquifer exists, if the overburden pressure acting on the water-saturated firn is above 0.12–0.14 MPa. This critical value of pressure was in good agreement with the overburden pressure obtained from depth–density curves of temperate glaciers. It was concluded that the depth of firn–ice transition was self-balanced by the overburden pressure to result in the concentration between 20 and 30 m.

scholarly journals Velocity distribution function of hydrogen atoms in ion source discharges

2021 ◽  
Author(s):  
Tatsuhiro Tokai ◽  
Yuji Shimabukuro ◽  
Hidenori Takahashi ◽  
Keita Bito ◽  
Motoi Wada
Keyword(s):  
Distribution Function ◽  
Velocity Distribution ◽  
Velocity Distribution Function ◽  
Ion Source ◽  
Hydrogen Atoms
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