Distribution of the Lifetimes of Energized Polyatomic Molecules in the Harmonic Model

1992 ◽  
Vol 57 (6) ◽  
pp. 1173-1176
Author(s):  
Milan Šolc
Keyword(s):  
Numerical Study ◽  
Critical Value ◽  
Polyatomic Molecules ◽  
Lifetime Distribution ◽  
Uniform Density ◽  
Harmonic Model ◽  
Unimolecular Reactions ◽  
Normal Vibrations ◽  
Harmonic Vibrations ◽  
Linearly Independent

In the harmonic model of unimolecular reactions of polyatomic molecules, the decay of a molecule is defined as the passage of an internal coordinate (given by the superposition of normal vibrations) over a critical value. A numerical study of the behaviour of the superposition of harmonic vibrations with frequencies linearly independent in the field of rationals has shown that the distribution of time gaps between upzeros of the superposition over the critical value is not exponential. For molecules with uniform density of phases, however, the lifetime distribution is close to an exponential one.

Natural Convection in a Cylindrical Enclosure Filled With Heat Generating Anisotropic Porous Medium

2001 ◽  
Vol 124 (1) ◽  
pp. 203-207 ◽  
Author(s):  
M. R. Dhanasekaran ◽  
Sarit Kumar Das ◽  
S. P. Venkateshan
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Critical Value ◽  
Permeability Ratio ◽  
Anisotropic Permeability ◽  
Anisotropic Porous Medium ◽  
Diffusivity Ratio

A numerical study has been made to analyze the effects of anisotropic permeability and thermal diffusivity on natural convection in a heat generating porous medium contained in a vertical cylindrical enclosure with isothermal wall and the top and bottom perfectly insulated surfaces. The results show that the anisotropies influence the flow field and heat transfer rate significantly. The non-dimensional maximum cavity temperature increases with increase in permeability ratio. For aspect ratio greater than or equal to two, the nondimensional maximum cavity temperature increases with an increase in the thermal diffusivity ratio. For aspect ratio equal to unity, there exists a critical value of thermal diffusivity ratio at which the maximum cavity temperature is a minimum. This critical value increases with an increase in the value of anisotropic permeability ratio. Based on a parametric study correlations for maximum cavity temperature and average Nusselt number are presented.

Numerical Study on the Migration of Two Spheres in Upward Pipe Flow

2018 ◽  
Author(s):  
Lei Liu ◽  
Haining Lu ◽  
Jianmin Yang ◽  
Xinliang Tian ◽  
Tao Peng ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Poiseuille Flow ◽  
Pipe Flow ◽  
Deep Sea ◽  
Numerical Study ◽  
Critical Value ◽  
Dynamic Responses ◽  
Phase Flow ◽  
Two Phase ◽  
Offshore Engineering

Migration of particles in pipe flow is commonly seen in offshore engineering, such as vertical transport of ores in deep sea mining. As the basis of the investigation on fluid-particle two-phase flow, the interaction of two spheres in upward pipe flow is studied by direct numerical simulations in this paper. The pipe flow is set as Poiseuille flow; the Reynolds number is no more than 1250. The dynamic responses of the spheres and the flow pattern are analyzed at different flow velocity. When compared to the sedimentation of two spheres in quiescent flow, the trailing sphere in Poiseuille flow will never surpass the leading one in Poiseuille flow. As the flow velocity increases in the pipe, the spheres are easier to separate after collision. When the flow velocity exceeds a critical value, the spheres will never collide.

Flow Dynamics of Vibrated Dense Granular Materials in the Presence of Ambient Gas

Volume 2 ◽  
2004 ◽  
Author(s):  
Azita Soleymani ◽  
Piroz Zamankhan ◽  
Hassan Yousefi ◽  
William Polashenski ◽  
Vesa Tanskanen
Keyword(s):  
Granular Materials ◽  
Numerical Study ◽  
Vertical Direction ◽  
Critical Value ◽  
Flow Dynamics ◽  
Particle Phase ◽  
Narrow Gap ◽  
Sinusoidal Oscillation ◽  
Interfacial Drag ◽  
The Continuum

Results are presented from a numerical study examining the flow dynamics of condensed granular materials in the presence of an interstitial gas in a narrow gap between two concentric cylindrical buckets subjected to sinusoidal oscillation in the vertical direction of the form z = Asin(ωt), where the parameter Γ = Aω2/g exceeds a critical value, Γc, above which the system becomes fluidized. Using a recently developed expression for the stress tensor of particle phase, a set of conservation equations were derived for the particle and fluid phases interacting via an interfacial drag force. Numerical integration of the continuum equations for the granular material in buckets revealed that above Γc, granular materials may exhibit liquid-like behavior and convection can occur creating a heap similar to that previously observed experimentally.

scholarly journals Numerical Study on Plane and Radial Wall Jets to Validate the 2D Assumption for an Idealized Downburst Outflow

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Yongli Zhong ◽  
Zhitao Yan ◽  
Yan Li ◽  
Jie Luo ◽  
Hua Zhang
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Critical Value ◽  
Plane Wall ◽  
Cloud Base ◽  
Jet Flows ◽  
Wall Jet ◽  
Wall Jets ◽  
Radial Wall ◽  
Velocity Decay

Turbulent radial and plane wall jets have been extensively investigated both experimentally and numerically over the past few decades. Previous studies mostly focused on the heat and mass transfers involved in jet flows. In this study, a comprehensive investigation was conducted on turbulent radial and plane wall jets, considering both jet spread and velocity decay for different parameters. The numerical results were compared with existing experimental measurements. The comparison focused on the velocity profile, jet spread, and velocity decay, and revealed that the Reynolds stress model (RSM) performs well in the simulation of both radial and plane wall jets. The results show that with a typical ratio of cloud base height to diameter for most downburst events, the effects of nozzle height and Reynolds number on the evolution of the radial wall jet are not significant. Both the jet spread and velocity decay exhibit a clear dependence on the Reynolds number below a critical value. Above this critical value, the plane wall jet becomes asymptotically independent of the Reynolds number. The co-flow was found to have a significant influence on the evolution of the plane wall jet. Comparatively, the jet spread and velocity of the radial wall jet were faster than those of the plane jet. For applications in civil engineering, it is valid to approximate the downburst outflow with a two-dimensional (2D) assumption from the perspective of longitudinal evolution of the flows.

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