Calculation Of Drift Velocity Research Articles

Numerical study of the motion of a single elongated bubble in high viscosity stagnant liquids along pipelines

Multiphase flow models involve more variables than available equations, thus closure relationships are required to solve the system of partial differential equations. In the Drift Flux Model, the mean drift velocity of the gas phase is estimate using the drift velocity closure relationship. This study investigates the motion of a single elongated bubble in high viscosity stagnant liquids in order to propose a comprehensive closure relationship for the bubble drift velocity. Different cases were run with inclination angles varying from 0° (horizontal direction) to 90° (vertical upward). OpenFOAM, an open source Computation Fluid Dynamics software, was used to numerically solve the two-phase incompressible flow problem. Drift velocities based on the movement of the bubble tip and the void fraction weighted averaged were compared to clarify the ambiguity in the drift velocity calculation and measurement. For horizontal pipe cases, the deformation of the bubble caused the drift velocity to be higher at the tip of the bubble than the drift velocity inside the bubble. For inclination angles more than 0°, the drift velocity at the tip is the same as inside the bubble. The closure relationship proposed is validated against experimental data in the literature. The results indicate that the closure relationship has a maximum 10% absolute average relative error for the viscosity range of 0.14–1.120 Pa·s, pipe size up to 0.152 m and pipe inclinations from 0° to 90°. The limitations of the closure relationship and potential enhancements for future studies are discussed.

Monte Carlo simulation of bulk semiconductors for accurate calculation of drift velocity as a parameter for drift-diffusion, hydrodynamic models

This paper describes the Monte Carlo (MC) method which can be used for evaluation of macroscopic parameters of semiconductors (eq. drift velocity, mobility). The major advantage of this approach is that it is strongly based on the physics and can be used to characterize many semiconductor materials. Here, results are presented for the bulk Silicon, GaAs and the 4H-SiC. For the 4H-SiC the 2d map of drift velocity as a function of electric field and temperature has been obtained.

Ionospheric drift measurements: Skymap points selection

In this paper we concentrate on the plasma drift measurement performed by Digisonde Portable Sounder DPS 4 developed by the UMLCAR, Lowell. Special attention is paid to the quality control of data acquired prior to drift velocity calculations. Risks of carefree use of raw Doppler spectra for the plasma motion analysis have been recognized in the Digisonde community. In this paper we propose improvements of Digisonde drift data processing for velocity evaluation and provide a detailed step‐by step description: (1) robust height range selection, (2) setting limits on the Doppler frequency shift, and (3) setting limits on the echo arrival angle. Raw data that passed our quality control were then used to derive three velocity components of the bulk plasma drift in the ionosphere. In the paper we discuss, in detail, application of the method on the DPS measurements. However, this technique can be efficiently applied on any other digital ionosondes drift data processing.

Molecular simulations of DNA transport in solution

A proposed novel nanotechnology concept utilizes tunneling conductance measurements across nanoelectrodes to identify individual nucleotides as a DNA strand crosses its path. Such a device offers the possibility of unprecedented rapidity in the detection of DNA sequences. Preliminary simulations of this device have indicated that single-stranded (ss)-DNA sequences behave differently depending on the location of the molecule within the device. Motivated by the similarity of the comparison of the transport properties of the ss-DNA molecule in bulk solution to experimental capillary electrophoresis data, we performed molecular dynamics (MD) simulations of ss-DNA and double-stranded (ds)-DNA in free solution to directly compare electrophoretic mobility as calculated by simulation. Drift velocity at the lowest magnitude applied electric field was consistent with expected experimental data; however, at the larger applied fields necessary under timescale constraints, drift velocity appeared inconsistent with extrapolated experimental values. The simulated electrophoretic mobility values resulting from the drift velocity calculations were also smaller than experiment.

Electron mobility and drift velocity calculations for bulk GaSb material

Electron mobility and drift velocity simulation results are presented for bulk GaSb based on a many-valley, anisotropic Monte Carlo model. Our mobility results at 300 K are in good agreement with available experimental data. Values close to the room temperature GaAs mobility have been predicted. Transient drift velocities are demonstrated to be higher than for GaAs and the negative differential velocity regime is shown to occur at much lower electric fields of about 1 kV/cm. The material could be useful as a low voltage oscillator or in high speed photodetection.

An ion-neutral species collision model for particle simulation of glow discharge

An ion-neutral species collision model with charge exchange is developed for use in particle simulation of a glow discharge based on an extension of the theory of Langevin (1905) and Hasse (1926). The validity of the model is checked by Monte Carlo calculation of drift velocity for He+-He, Ne+-Ne, Ar+-Ar and Kr+-Kr collisions. The results show good agreement with the experimental data and the solution by the moment method, especially for heavy gases. By proper choice of the cut-off value of the dimensionless impact parameter in the model, it is applicable to a collision of ions of energy 1 keV.

The transport and ionization coefficients of hot electrons in rare gas liquids and liquids with molecular impurities

The results of calculations of drift velocity, transverse, longitudinal diffusion coefficients and characteristic energies, and ionization coefficients for pure atomic liquid and solutions with molecular impurities are reported. The features of hot electrons kinetics are discussed.

Collisions of H+, H2+, H3+, ArH+, H−, H, and H2 with Ar and of Ar+ and ArH+ with H2 for Energies from 0.1 eV to 10 keV

Graphical and tabulated data and the associated bibliography are presented for cross sections for elastic, excitation, and ionization collisions of H+, H+2, H+3, ArH+, H−, H, and H2 with Ar and of Ar+ and ArH+ with H2 for laboratory energies from 0.1 eV to 10 keV. Where appropriate, drift velocities and reaction or excitation coefficients are calculated from the cross sections and are recommended for use in analyses of swarm experiments and electrical discharges. In the case of H+ in Ar, cross sections for momentum transfer, charge transfer, electronic excitation, and electron production are recommended. Drift velocity calculations predict runaway for H+ in Ar for electric field to gas density ratios E/n greater than 4.3×10−18 V m2. For H+2 in Ar, the cross sections include those for ArH+ formation, charge transfer, electronic excitation, and electron production. Drift velocities and average cross sections are calculated versus E/n. In the case of ArH+ collisions with Ar, only cross sections for ion molecule reactions are recommended. For H− collisions with Ar only collisional detachment data is available. Momentum transfer, electronic excitation, and electron production cross section data are available for collisions of H with Ar. Collisions of H with Ar are of special interest because of the very large cross sections for excitation of the H atoms at low energies. For H2 in Ar cross sections for momentum transfer and excitation of the Hα and Hβ lines are recommended. For Ar+ collisions with H2, cross sections for charge transfer and ion molecule reactions are recommended. Cross sections for proton transfer are available for ArH+ in H2.

Cross Sections and Swarm Coefficients for Nitrogen Ions and Neutrals in N2 and Argon Ions and Neutrals in Ar for Energies from 0.1 eV to 10 keV

Graphical and tabulated data and the associated bibliography are presented for cross sections for elastic, excitation, and ionization collisions of N+, N+2, N, and N2 with N2 and for Ar+ and Ar with Ar for laboratory energies from 0.1 eV to 10 keV. Where appropriate, drift velocities and reaction or excitation coefficients are calculated from the cross sections and recommended for use in analyses of swarm experiments and electrical discharges. In the case of N+ in N2, cross sections for momentum transfer, charge transfer, electronic excitation, and electron production are recommended. Drift velocity calculations predict runaway for N+ in N2 for electric field to gas density ratios E/n greater than 4.3×103 Td, where 1 Td (townsend)=10−21 V m2. For N+2 in N2, the cross sections include those for N+ and N+3 formation, electronic excitation, and electron production. Drift velocities and average cross sections are calculated for E/n≥500 Td. In the case of N in N2, only cross sections for momentum transfer are recommended. For N2 in N2, cross sections for momentum transfer, electronic excitation, and electron production are recommended. Collisions of electronically excited states with N2 are not included. For Ar+ in Ar, cross sections for charge transfer, electronic excitation, and electron production are recommended. For Ar in Ar, cross sections for momentum transfer, electronic excitation, and electron production are recommended.

Cross Sections and Swarm Coefficients for H+, H2+, H3+, H, H2, and H− in H2 for Energies from 0.1 eV to 10 keV

Graphical and tabulated data and the associated bibliography are presented for cross sections for elastic, excitation and ionization collisions of H+, H2+, H3+, H, H2, and H− with H2 at laboratory energies from 0.1 to 10 keV. Where appropriate, drift velocities and reaction or excitation coefficients are calculated from the cross sections and recommended for use in analyses of swarm experiments and electrical discharges. In the case of H+ in H2, cross sections for momentum transfer, rotational excitation, vibrational excitation, charge transfer, electronic excitation, and ionization are recommended. Energy-loss or stopping-power coefficients calculated from these cross sections are much smaller than obtained from stopping-power theory. There are no relevant energy-loss experiments for H+ in H2. Drift velocity calculations predict runaway for H+ in H2 for electric field to gas density ratios E/n greater than 700 Td, where 1 Td (townsend)=10−21 V m2. For H2+ in H2, the cross sections include H3+ formation, charge transfer, vibrational and electronic excitation, and ionization. Drift velocities and average cross sections are calculated for E/n≥1 kTd. For H3+ in H2, cross sections for momentum transfer, various charge transfer processes, electronic excitation, and ionization and drift velocities are recommended. In the case of H in H2, cross sections for momentum transfer, rotational excitation, vibrational excitation, charge transfer, H− formation, electronic excitation, and ionization are recommended. For H2 in H2, cross sections for momentum transfer, rotational excitation, vibrational excitation, charge transfer, electronic excitation, and ionization are recommended. In the case of H− in H2, cross sections for momentum transfer, electron detachment, and ionization are recommended and calculated drift velocities are compared with experiment. Collisions of electronically excited states with H2 are not included.

Calculations of drift velocity of electrons in inert gases at low E/N

The zero field reduced mobilities of electrons μ0 in helium, neon, argon, krypton, and xenon have been calculated as a function of gas temperatures T using the Boltzmann equation and compared with the values of the thermal electron mobilities of electrons μN obtained by Mozumder [J. Chem. Phys. 72, 6289 (1980)]. Discussion has been made about the large discrepancies between the measured and calculated values of μN in neon which were pointed out by Mozumder. The calculated exact drift velocities W in helium as a function of E/N and T have been compared with the experimental results of W for wide E/N and T ranges. A summarized figure is shown for anomalous electron mobilities in helium as a function of N at low E/N.

Drift motion and perpendicular diffusion of energetic particles in interplanetary space based on spacecraft data

A realistic model of the interplanetary magnetic field (IMF) is constructed based on measurements taken by Pioneer 10 magnetometer at 5 AU. Energetic particle (0.1–100 MeV) propagation in this field is studied by a computer simulation of its motion in order to calculateK⊥, the perpendicular diffusion coefficient, and 〈V D 〉 the average drift velocity of an ensemble of particles. Determinations ofK⊥ lie in the range 3×1019–8×1020 cm2 s−1 for the energies considered and they show that perpendicular diffusion may be an important process at these heliodistances when compared with parallel diffusion results obtained by similar techniques, contrary to what was previously thought. Drift velocity calculations are very close to predictions of guiding centre theory (within 30%) suggesting that this theory can be applied in the IMF. This result shows that gradient and curvature drifts can be present even in a highly perturbed field and thus they can have some influence in cosmic ray modulation.

Monte Carlo calculation of hot electron drift velocity in silicon (100)-inversion layer by including three subbands

A Monte Carlo calculation of the drift velocity of hot electrons in quantized silicon inversion layers for (100)-oriented surface has been performed by considering the three lowest subbands. The intersubband and intervalley phonons conform to the surface Brillouin zone structure and are assumed to have bulk values of deformation potential constants. It is found that most of the electrons tend to occupy the E 0′ subband at about 10 kV cm -1. The effect of surface-oxide-charge scattering is found to be quite important. The calculated curves show a change of slope at about 10 kV cm -1 and do not show clear saturation. This is in contrast with the experimental curve which shows first a smooth variation and then tends to saturate.

Monte Carlo calculation of the electron drift velocity in GaAs with a superlattice

Monte Carlo calculations of the drift velocity and mean energy vs electric field in n-type GaAs with a superlattice are reported. The model allows for phonon scattering, and a simple sinusoidal band shape in the direction of the superlattice is assumed. Negative differential mobility and energy saturation appear, and their variation with lattice temperature and miniband width is discussed. The threshold field decreases and the absolute value of the differential mobility increases with decreasing lattice temperature, while the miniband width has minor influence on these parameters. Schockley streaming is observed at low lattice temperature.

Optimum semiconductor for microwave devices

The best semiconductors for microwave devices, silicon and gallium arsenide, are restricted in their performance because the electron drift velocity saturates at a fairly low value. It is proposed that InAs-InP alloys should give better performance. Detailed calculations of drift velocity are made by a Monte Carlo technique, and it is shown that some alloys should give drift velocities greater than 4×107cm/s.

Calculation of drift velocity in silicon at high electric fields†

Abstract Drift velocity in n and p-type silicon is calculated using the Monto Carlo method to determine the current carrier distribution. Agreement with recent measurements for high field drift velocity is good. Carrier-lattice scattering rates for p-type silicon were determined from low field mobility versus temperature. D. Long's model was used for n-type silicon.

Effect of nonparabolicity on drift velocity in GaAs

Incorporation of nonparabolicity of the (100) valley into our calculations of drift velocity versus field in GaAs has raised the beginning of the negative differential mobility region from 2.1 to 2.9 kV/cm and the valley field from 10 to 12 kV/cm for the same model and parameters as used earlier.