The effect of aspect ratio on longitudinal diffusivity in rectangular channels

1982 ◽  
Vol 120 ◽  
pp. 347-358 ◽  
Author(s):  
P. C. Chatwin ◽  
Paul J. Sullivan
Keyword(s):  
Laminar Flow ◽  
Aspect Ratio ◽  
Cross Section ◽  
Laboratory Experiments ◽  
Rectangular Cross Section ◽  
Independent Method ◽  
Surprising Result ◽  
Large Aspect Ratio ◽  
Rectangular Channels ◽  
Side Walls

In a recent paper Doshi, Daiya & Gill (1978) showed that the value of Taylor's longitudinal diffusivity D for laminar flow in a channel of rectangular cross-section of breadth u and height b is about 8D0, for large values of the aspect ratio a/b, where Do is the value of the longitudinal diffusivity obtained by ignoring all variation across the channel. This superficially surprising result is confirmed by an independent method, and is shown to be caused by the boundary layers on the side walls of the channel. The primary purpose of the paper, however, is to consider the value of D in turbulent flow in a flat-bottomed channel of large aspect ratio, for which arguments based on physics are adduced in support of the formula D≈[1 + B][1 - λ(b/u)], where B and λ are positive constants independent of b. It is shown that this result is consistent with laboratory experiments by Fischer (1966). The paper concludes with a discussion of the practical effects of aspect ratio on longitudinal dispersion in channels whose cross-section is approximately rectangular.

Dependence of AC losses on aspect ratio in superconducting wires with rectangular cross section

2004 ◽  
Vol 412-414 ◽  
pp. 1045-1049 ◽  
Author(s):  
K. Kajikawa ◽  
T. Hayashi ◽  
K. Funaki ◽  
E.S. Otabe ◽  
T. Matsushita
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Ac Losses ◽  
Superconducting Wires

scholarly journals Формирование и деформация капель жидкости в микроканалах

2020 ◽  
Vol 46 (15) ◽  
pp. 18
Author(s):  
Ф.В. Роньшин ◽  
Ю.А. Дементьев ◽  
Е.А. Чиннов
Keyword(s):  
Experimental Study ◽  
Flow Regime ◽  
Cross Section ◽  
Weber Number ◽  
Rectangular Cross Section ◽  
Critical Value ◽  
Drop Formation ◽  
Liquid Bridges ◽  
Liquid Moving ◽  
Side Walls

An experimental study of drop formation in narrow horizontal microchannels with rectangular cross section and a height from 50 to 150 micrometers was performed. It is shown that in these channels there is a new flow regime when drops moving along the microchannel, which are vertical liquid bridges. Three mechanisms of the formation of such drops are distinguished: the formation directly near the liquid nozzle, the separation of droplets from the liquid moving along the side walls of the channel, and due to the destruction of strongly deformed drops and horizontal liquid bridges. It was found that the deformation of drops increases with an increase in the Weber number. It is shown that when the first critical value of the Weber number is reached, the drops begin to deform, and when the second Weber number is reached, they break.

Heat Transfer for Laminar Flow in Spiral Ducts of Rectangular Cross Section

2005 ◽  
Vol 127 (3) ◽  
pp. 352-356 ◽  
Author(s):  
Michael W. Egner ◽  
Louis C. Burmeister
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Radius Of Curvature ◽  
Dean Number ◽  
Aspect Ratios ◽  
Small Pitch

Laminar flow and heat transfer in three-dimensional spiral ducts of rectangular cross section with aspect ratios of 1, 4, and 8 were determined by making use of the FLUENT computational fluid dynamics program. The peripherally averaged Nusselt number is presented as a function of distance from the inlet and of the Dean number. Fully developed values of the Nusselt number for a constant-radius-of-curvature duct, either toroidal or helical with small pitch, can be used to predict those quantities for the spiral duct in postentry regions. These results are applicable to spiral-plate heat exchangers.

scholarly journals Flow through a helical pipe with rectangular cross-section

1970 ◽  
Vol 4 (2) ◽  
pp. 99-110
Author(s):  
Md Mahmud Alam ◽  
Delowara Begum ◽  
K Yamamoto
Keyword(s):  
Aspect Ratio ◽  
Iterative Method ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Main Tool ◽  
Numerical Approach ◽  
Dean Number ◽  
Helical Pipe ◽  
Flow Through ◽  
Marine Engineering

The effects of torsion, aspect ratio and curvature on the flow in a helical pipe of rectangular cross- section are studied by introducing a non-orthogonal helical coordinate system. Spectral method is applied as main tool for numerical approach where Chebyshev polynomial is used. The numerical calculations are obtained by the iterative method. The calculations are carried out for 0≤ δ ≤0.02, 1≤ λ ≤ 2.85, 1≤ γ ≤2.4, at Dn = 50 & 100 respectively, where d is the non-dimensional curvature, l the torsion parameter, g the aspect ratio and  Dn the pressure driven parameter (Dean number).DOI: http://dx.doi.org/10.3329/jname.v4i2.991 Journal of Naval Architecture and Marine Engineering Vol.4(2) 2007 p.99-110

Influence of the Cross-Section on the Erosion Criteria for Partly Cohesive Sediments

1994 ◽  
Vol 29 (1-2) ◽  
pp. 103-111 ◽  
Author(s):  
Hilde Torfs ◽  
Marc Huygens ◽  
Limbaya Tito
Keyword(s):  
Sediment Transport ◽  
Cross Section ◽  
Cross Sections ◽  
Cohesive Sediments ◽  
Material Content ◽  
Rectangular Channels ◽  
Side Walls ◽  
Mixed Sediments ◽  
Sediment Mixture ◽  
Cohesive Material

Erosion of sediment mixtures, comprising cohesive as well as non-cohesive sediments, has been studied in straight laboratory flumes of circular and rectangular cross-sections. Erosion of mixed sediments depended on the mixture composition (cohesive material content), the type of cohesive sediment, and the shape of the flume cross-section. By increasing the cohesive material content, the erosion resistance of the sediment mixture also increased and the erosion pattern changed from ripples and dunes (noncohesive) to a groove or wavy surface (cohesive). In circular channels, the influence of the “side” walls on sediment transport is important, but the criteria for incipient motion seem to be the same as in the rectangular channels. Hence, sediment transport models developed for rectangular channels cannot be readily applied to circular channels.

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