Evaluation of longitudinal dispersion coefficients for over-bank flow

2004 ◽  
pp. 1245-1249
Author(s):  
Steve Wallis ◽  
J Manson
Keyword(s):  
Longitudinal Dispersion ◽  
Dispersion Coefficients

Longitudinal dispersion coefficients of pollutants in compound channels with vegetated floodplains

2018 ◽  
Vol 31 (4) ◽  
pp. 740-749 ◽  
Author(s):  
Li Gu ◽  
Xin-xin Zhao ◽  
Ling-hang Xing ◽  
Zi-nan Jiao ◽  
Zu-lin Hua ◽  
...  
Keyword(s):  
Longitudinal Dispersion ◽  
Dispersion Coefficients ◽  
Compound Channels

A Mathematical and Experimental Examination of Transverse Dispersion Coefficients

1968 ◽  
Vol 8 (02) ◽  
pp. 195-204 ◽  
Author(s):  
Robert C. Hassinger ◽  
Dale U. Von Rosenberg
Keyword(s):  
Porous Medium ◽  
Dispersion Coefficient ◽  
Packed Column ◽  
Packing Material ◽  
Longitudinal Dispersion ◽  
Physical Parameters ◽  
Dispersion Coefficients ◽  
Molecular Diffusivity ◽  
Transverse Dispersion ◽  
Wide Range

Abstract Transverse dispersion has received considerably less treatment in the literature than has longitudinal dispersion. Different methods for determining transverse dispersion coefficients have been used in different investigations, and the results obtained have not been consistent enough to permit accurate generalizations as to the effect of various physical parameters on the magnitude of these coefficients. A numerical solution to the differential equation describing transverse dispersion in the absence of longitudinal dispersion was obtained to enable one to calculate the dispersion coefficient from experimental results. The more general dispersion equation including longitudinal dispersion also was solved numerically to give quantitative limits of a dimensionless group within which the assumption of negligible longitudinal dispersion is justified. Possible experimental procedures were examined, and one utilizing a cylindrical packed column was chosen for the determination of transverse dispersion coefficients. Values of these coefficients were determined for a system of two miscible organic fluids of equal density and viscosity, for two sizes of packing material over a wide range of flow rates in the laminar regime. The dispersion coefficient was found to decrease, for a constant value of the product of packing size and interstitial velocity, as the size of the packing material particles increased. Introduction Longitudinal dispersion has received extensive treatment in the literature, and consequently is better understood than its orthogonal counterpart, transverse dispersion. Many mathematical models of dispersion processes assume that transverse dispersion is rapid enough to damp out any radial concentration gradients and therefore may be neglected. Laboratory and production results, however, indicate that this is a poor assumption. Various experimental procedures for determining transverse dispersion coefficients have been used in previous investigations, but the results have generally been expressed by similar correlations. The transverse dispersion coefficients obtained, however, have often varied considerably for given values of the correlation parameters. We feel that further experimental determinations of transverse dispersion coefficients will help alleviate some of the inconsistencies in these empirical correlations. One assumption implicit in all previous investigations is that of negligible longitudinal dispersion in the experimental system. An attempt to justify this assumption often is made using intuitive reasoning, but it is apparent that this reasoning must break down as the condition of zero flow rate is approached. A mathematical examination of the equations describing the system yields physical limits outside of which the assumption of negligible longitudinal dispersion is invalid. Background In a porous medium, the "effective molecular diffusivity" De is less than the molecular diffusivity D measured in the absence of a porous medium, due to the tortuous path which a diffusing molecule must travel. Various authors have reported values of the ratio De/D in the range of 0.6 to 0.7. When there is fluid flow within the porous medium, mass transfer occurs by convective dispersion as well as by molecular diffusion. These are separate phenomena and can be treated as such on a microscopic scale. However, the mathematical complexity is such that only extremely simple geometries could be considered, and the results hardly would be applicable to the complex geometries existent in actual porous media. SPEJ P. 195ˆ

scholarly journals Laboratory Determination of Transverse and Longitudinal Dispersion coefficients in Porous Media

1996 ◽  
Vol 38 (1) ◽  
pp. 13-27 ◽  
Author(s):  
Makoto NISHIGAKI ◽  
Teddy SUDINDA ◽  
Y. SASAKI ◽  
M. INOUE ◽  
T. MORIWAKI
Keyword(s):  
Porous Media ◽  
Longitudinal Dispersion ◽  
Dispersion Coefficients ◽  
Laboratory Determination

Longitudinal dispersion of matter due to the shear effect of steady and oscillatory currents

1984 ◽  
Vol 148 ◽  
pp. 383-403 ◽  
Author(s):  
Hidekazu Yasuda
Keyword(s):  
Line Source ◽  
Dispersion Coefficient ◽  
Longitudinal Dispersion ◽  
Shear Effect ◽  
Two Dimensional ◽  
Clear Definition ◽  
Dispersion Coefficients ◽  
Initial Stage ◽  
Definition Of ◽  
A Current

The longitudinal dispersion due to the shear effect of a current is examined theoretically in the idealized two-dimensional case. This study reveals the process whereby the dispersion reaches a stationary stage after the release of the dispersing substance as an instantaneous line source in steady and in oscillatory currents. In addition, the relation between the stationary dispersion coefficients in steady and oscillatory currents is given analytically. Analysis of the dispersion during the initial stage needs a clear definition of the vertical average of the variance. We can understand the problem of the negative dispersion coefficient, which is obtained by the usual vertical average, through introduction of a new vertical average.

Dispersion coefficients of sewers from tracer experiments

2005 ◽  
Vol 52 (5) ◽  
pp. 123-133 ◽  
Author(s):  
J. Rieckermann ◽  
M. Neumann ◽  
C. Ort ◽  
J.L. Huisman ◽  
W. Gujer
Keyword(s):  
Longitudinal Dispersion ◽  
Flow Conditions ◽  
Dispersion Coefficients ◽  
Engineering Applications ◽  
High Degree ◽  
Stable Flow ◽  
Dry Weather Flow ◽  
Tracer Experiments

In this paper, 60 tracer experiments in 37 different sewer reaches have been analyzed for longitudinal dispersion under dry weather flow conditions. It was found that dispersion coefficients of sewers are two to three orders of magnitude smaller than those measured in rivers and do not differ much from system to system. Suitable equations were identified to predict reasonable dispersion coefficients in sewer reaches with uniform geometry and stable flow conditions. For engineering applications that require a high degree of accuracy the performance of tracer measurements is recommended.

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