Diffusion in Three-Component Gas Mixtures in Transition Region between Knudsen and Molecular Diffusion

1968 ◽  
Vol 7 (3) ◽  
pp. 429-432 ◽  
Author(s):  
R. S. Cunningham ◽  
C. J. Geankoplis
Keyword(s):  
Transition Region ◽  
Molecular Diffusion ◽  
Gas Mixtures

scholarly journals Numerical Investigation into the Flow Characteristics of Gas Mixtures in Knudsen Pump with Variable Soft Sphere Model

Micromachines ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 784
Author(s):  
Chunlin Du ◽  
Xiaowei Wang ◽  
Feng Han ◽  
Xiaoyu Ren ◽  
Zhijun Zhang
Keyword(s):  
Flow Pattern ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Flow ◽  
Molecular Diffusion ◽  
Flow Characteristics ◽  
Gas Mixtures ◽  
Soft Sphere ◽  
Knudsen Pump

In Knudsen pumps with geometric configuration of rectangle, gas flows are induced by temperature gradients along channel walls. In this paper, the direct simulation Monte Carlo (DSMC) method is used to investigate numerically the flow characteristics of H2–N2 mixtures in the Knudsen pump. The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures, and the results obtained are compared with those calculated from a variable hard sphere (VHS) model. It is demonstrated that pressure is crucial to affecting the variation of gas flow pattern, but the gas concentration in H2–N2 mixtures and the collision model do not change the flow pattern significantly. On the other hand, the velocity of H2 is larger than that of N2. The velocities of H2 and N2 increase if the concentration of H2 rises in the gas mixtures. The results of velocity and mass flow rate obtained from VSS and VHS models are different. Finally, a linear relation between the decrease of mass flow rate and the increase of H2 concentration is proposed to predict the mass flow rate in H2–N2 mixtures.

scholarly journals Numerical Simulation of Nanosilica Sol Grouting for Deep Tunnels Based on the Multifield Coupling Mechanism

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Dongjiang Pan ◽  
Kairong Hong ◽  
Helin Fu ◽  
Zhiguo Li ◽  
Limeng Zhang ◽  
...  
Keyword(s):  
Physical Properties ◽  
Transition Region ◽  
Molecular Diffusion ◽  
Initial Permeability ◽  
Silica Sol ◽  
Water Diversion ◽  
Coupling Mechanism ◽  
Mechanical Dispersion ◽  
Grouting Pressure ◽  
Geological Conditions

Grouting is an effective technical way for the construction of deep tunnels in unfavorable geological conditions. The fluid-solid-chemical coupling mechanism of grouting process is analyzed from the following three aspects: influence of physical properties of silica sol on permeability coefficient, dynamic changes of porosity and permeability of geotechnical media with seepage pressure, and governing equations for flow and mass transfer characteristics. A dynamically changing model for nanosilica sol grouting in deep tunnels is established, considering the changing physical properties of grout and surrounding rock. Based on the Xianglushan Tunnel of Yunnan Water Diversion Project, the temporal and spatial evolution of silica sol grout is studied. The effect characteristics of grouting pressure and initial permeability are clarified. The rationality of this model is verified by classical Newtonian fluid grouting theory. The main conclusions: with the molar concentration as the index, the grout range can be divided into the raw grout region and the transition region; with the decrease of the grouting pressure, the growth rate of the normal grouting radius and the axial grouting radius will gradually decrease; due to the mechanical dispersion and molecular diffusion, the range of the transition region will gradually increase with time. The ratio of the transition region to grouting radius fluctuates slightly with time under the initial permeability of 5 D. The fluctuation increases with the decrease of initial permeability, and the average ratio increases with the decrease of grouting pressure. This study can provide theoretical guidance for grouting design of deep tunnel engineering.

Effects of Ambipolar Diffusion on Prominence Thread Models

1994 ◽  
Vol 144 ◽  
pp. 315-321 ◽  
Author(s):  
M. G. Rovira ◽  
J. M. Fontenla ◽  
J.-C. Vial ◽  
P. Gouttebroze
Keyword(s):  
Energy Balance ◽  
Transition Region ◽  
Ambipolar Diffusion ◽  
Line Profiles ◽  
Balance Equations ◽  
Model Calculations ◽  
Partial Frequency ◽  
Frequency Redistribution ◽  
Partial Frequency Redistribution ◽  
Theoretical Structure

AbstractWe have improved previous model calculations of the prominence-corona transition region including the effect of the ambipolar diffusion in the statistical equilibrium and energy balance equations. We show its influence on the different parameters that characterize the resulting prominence theoretical structure. We take into account the effect of the partial frequency redistribution (PRD) in the line profiles and total intensities calculations.

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