An effect of entrance length on development of velocity profile in channel of millimeter dimensions

2016 ◽  
Author(s):  
D. Jasikova ◽  
M. Kotek ◽  
V. Kopecky
Keyword(s):  
Velocity Profile ◽  
Entrance Length

Analytical Modelling of Laminar Developing Flow Between Hydrophobic Surfaces with Different Slip-Velocities

2021 ◽  
Author(s):  
Sankar Vijay ◽  
Jaimon Cletus ◽  
Arun MG ◽  
Ranjith S Kumar
Keyword(s):  
Velocity Profile ◽  
Slip Length ◽  
Central Line ◽  
Momentum Equation ◽  
Layer Growth ◽  
Parallel Plates ◽  
Entrance Length ◽  
Navier Slip ◽  
Free Region ◽  
Separation Of Variable

Abstract Theoretical analysis of the entrance hydrodynamics of microchannels is an important design aspect in connection with the development of microfluidic devices. In this paper, pressure-driven fluid flow in the entrance region of two infinite hydrophobic parallel plates with dissimilar slip-velocities is analytically modelled. The linearized momentum equation is solved by applying the Navier-slip model at the boundaries to achieve the most generalized two-dimensional form. The velocity profile is obtained by combining the developed and developing velocities, which is estimated by invoking the separation of variable method. It is observed that the velocity profile is asymmetric and the shear-free region can be shifted from the geometrical central line by altering the wall hydrophobicity. Moreover, the zero shear zone is transferred more towards the surface having high hydrophobicity. The expression for wall shear stress is obtained analytically using Newton's law of viscosity. Moreover, the boundary layer growth from the upper and lower walls are found to be entirely different and they merge at the entrance length and is noticed to be off-setted from the geometric centre-line. The effect of slip-length on the entrance length is analysed and an empirical correlation is deduced.

Hydrodynamic Entrance Lengths for Ducts of Arbitrary Cross Section

1967 ◽  
Vol 89 (4) ◽  
pp. 847-850 ◽  
Author(s):  
S. T. McComas
Keyword(s):  
Velocity Profile ◽  
Detailed Analysis ◽  
Cross Section ◽  
Analytical Method ◽  
Arbitrary Cross Section ◽  
Numerical Results ◽  
Entrance Length ◽  
Flow Development

A general analytical method is presented for determination of the hydrodynamic entrance length of ducts of arbitrary cross section. Only knowledge of the fully developed velocity profile is required in order to determine this length in comparison to other approaches which require a detailed analysis of the flow development. This method is applied to circular, elliptical, annular, rectangular, and triangular ducts with numerical results presented.

Microchannel Flow Measurement Using Micro Particle Image Velocimetry

2002 ◽  
Author(s):  
Sang-Youp Lee ◽  
Steven T. Wereley ◽  
Lichuan Gui ◽  
Weilin Qu ◽  
Issam Mudawar
Keyword(s):  
Particle Image Velocimetry ◽  
Laminar Flow ◽  
Velocity Profile ◽  
Particle Image ◽  
Velocity Profiles ◽  
Entrance Length ◽  
Number Range ◽  
Micro Particle Image Velocimetry ◽  
Peak Broadening ◽  
Image Velocimetry

Since microfabrication techniques are typically planar processes, microchannel flows typically have significant predevelopment due to the upstream reservoir having the same height as the microchannel. The main concerns of the current study are categorized into finding the effects of typical microchannel geometry on the velocity entrance length in the laminar flow regime and providing the turbulence transitional Reynolds number range using the details of the velocity profile rather than global measurements of pressure drop. A rectangular micro-channel of aspect ratio ∼2.65 and the hydraulic diameter 380μm was used in this study. Micro particle image velocimetry measurement was performed to measure the velocity profiles. The entrance length is reduced about 45% and the transitional velocity profile is measured at Re=2900. The velocity profiles do not show deviation from the fully developed laminar flow profiles up to Re=2100. Related to the flow transition, the close resemblance between the correlation function peak broadening and the turbulence intensity is observed.

Investigation of the influence of the flow structure on the accuracy of flow measurement before a hydrometric structure in an open channel

2020 ◽  
pp. 41-44
Author(s):  
Anatoly Kusher
Keyword(s):  
Velocity Profile ◽  
Flow Velocity ◽  
Water Flow ◽  
Flow Measurement ◽  
Water Discharge ◽  
Critical Depth ◽  
Flow Measurements ◽  
Study Results ◽  
Flow Velocity Profile ◽  
Upstream Flow

The reliability of water flow measurement in irrigational canals depends on the measurement method and design features of the flow-measuring structure and the upstream flow velocity profile. The flow velocity profile is a function of the channel geometry and wall roughness. The article presents the study results of the influence of the upstream flow velocity profile on the discharge measurement accuracy. For this, the physical and numerical modeling of two structures was carried out: a critical depth flume and a hydrometric overfall in a rectangular channel. According to the data of numerical simulation of the critical depth flume with a uniform and parabolic (1/7) velocity profile in the upstream channel, the values of water discharge differ very little from the experimental values in the laboratory model with a similar geometry (δ < 2 %). In contrast to the critical depth flume, a change in the velocity profile only due to an increase in the height of the bottom roughness by 3 mm causes a decrease of the overfall discharge coefficient by 4…5 %. According to the results of the numerical and physical modeling, it was found that an increase of backwater by hydrometric structure reduces the influence of the upstream flow velocity profile and increases the reliability of water flow measurements.

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