Anomalous Transition to Turbulence in Microtubes

2000 ◽  
Author(s):  
Kendra V. Sharp ◽  
Ronald J. Adrian ◽  
David J. Beebe
Keyword(s):  
Flow Resistance ◽  
Particle Image ◽  
Scale Effects ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Micro Scale ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv ◽  
Microscale Flow ◽  
Image Velocimetry

Abstract As the microfluidics field expands, required flowrates in microdevices are expected to span a large range of Reynolds numbers (Re), and the prediction of flow regime, namely laminar versus turbulent, is highly relevant. Recent measurements have been inconclusive in answering a fundamental question: Does microscale flow behave differently than macroscale flow? Previous measurements have suggested that the transition to turbulence occurs at Re much lower than 2000, the generally accepted lower limit of macroscale transition to turbulence. The current experiments use both bulk flow resistance measurements and micro-Particle Image Velocimetry (micro-PIV) results to show that, for Re < 1100–1500 and microchannel diameters 75 to 250 μm, the velocity profiles and flow resistance are well-predicted by macroscale laminar flow theory. For Re > 1100–1500, an initial departure from laminar behavior is noted both from the flow resistance and the micro-PIV experiments. Thus, some “micro-scale” effects are observed, though they are not as dramatic as those observed in previous studies. A brief literature review of transitional macroscale pipe flow is presented, and potential explanations are proposed for the possible “micro-scale” effects observed in these experiments.

Three-Dimensional Micro-Flow Measurement in a Capillary with a Diode Laser Micro-Particle Image Velocitometry

2006 ◽  
Vol 505-507 ◽  
pp. 343-348
Author(s):  
C.T. Pan ◽  
P.J. Cheng ◽  
Yeong-Maw Hwang ◽  
M.F. Chen ◽  
H.S. Chuang ◽  
...  
Keyword(s):  
Diode Laser ◽  
Particle Image ◽  
Three Dimensional ◽  
Calibration Method ◽  
Measurement Range ◽  
Scanning Method ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv ◽  
Image Velocimetry ◽  
Micro Flow

A self-built micro-particle image velocimetry (micro-PIV) with a diode laser is established to measure the micro-fluidic phenomenon in a 100 μm rectangular capillary. By scanning method, a 3-D flow image with a flowrate of 0.3 μL/min is presented. With this calibration method, the measurement ability for 3-D micro-fluidic dynamics could be achieved. This technique also reveals its benefit and potential in metrology. Hence, it provides a helpful tool for Bio-MEMS research. The experiment is proceeded under laminar flow, Re= 0.011. The measurement range is ranging from 0.05μm/s to 4.3mm/s. The vector grid resolution is optimized to 2.5 μm.

Infrared Micro-Particle Image Velocimetry of Fluid Flow in Silicon-Based Microdevices

Volume 4 ◽  
2004 ◽  
Author(s):  
Dong Liu ◽  
Suresh V. Garimella ◽  
Steve T. Wereley
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Capillary Tube ◽  
Surface Flow ◽  
Mems Devices ◽  
Flow Measurements ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv ◽  
Image Velocimetry ◽  
Silicon Based

A non-intrusive diagnostic technique, infrared micro-particle image velocimetry (IR-PIV), is developed for measuring flow fields within MEMS devices with micron-scale resolution. This technique capitalizes on the transparency of silicon in the infrared region, and overcomes the limitation posed by the lack of optical access with visible light to sub-surface flow in silicon-based micro-structures. Experiments with laminar flow of water in a circular micro-capillary tube of hydraulic diameter 255 μm demonstrate the efficacy of this technique. The experimental measurements agree very well with velocity profiles predicted from laminar theory. Cross-correlation and auto-correlation algorithms are employed to measure very-low and moderate-to-high velocities, respectively; the former approach is suitable for biomedical applications while the latter would be needed for measurements in electronics cooling. The results indicate that the IR-PIV technique effectively extends the application of regular micro-PIV techniques, and has great potential for flow measurements in silicon-based microdevices.

Experimental Investigation of Blood Cells Flowing Through Microscale Geometries Using MicroPIV

2012 ◽  
Author(s):  
Vishwanath Somashekar ◽  
Michael G. Olsen ◽  
K. B. Chandran ◽  
H. S. Udaykumar
Keyword(s):  
Particle Image Velocimetry ◽  
Platelet Activation ◽  
Blood Cells ◽  
Particle Image ◽  
Mechanical Heart Valve ◽  
Reynolds Numbers ◽  
High Shear ◽  
Endothelial Layer ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry

The advances made in the field of cardiovascular prostheses have proved invaluable in saving human lives. However, implanting such a device may cause unwanted results like thrombosis, the formation of blood clots inside blood vessels. This formation of thrombi can affect the flow of blood, which if left untreated may result in strokes. As the blood moves through various arteries and veins, the platelets move toward the periphery and the red blood cells (RBC) are more concentrated near the center. This process is called margination and has been shown by Aarts et al.[1]. The platelets in essence are policing the endothelial layer, and with any change in the endothelial layer, say as a result of injury, the platelets get activated, which in turn starts a domino effect eventually resulting in the formation of a clot to stop the bleeding. These platelets can also get activated due to their presence in regions of high shear as is the case when the blood is flowing through narrow constrictions (for example, when a mechanical heart valve is about to close). This phenomenon is referred to as Shear Induced Platelet Activation (SIPA)[2]. The goal of this research is to study the effect of constricted geometries, high shear rates and erythrocyte-platelet interactions on platelet activation and aggregate formation, events that are critical in the initiation of thrombosis. In order to understand SIPA, one must first obtain a detailed flow in these constricted geometries. Numerous studies have been performed to obtain the flow fields of blood flowing through microchannels [3, 4]. However, the Reynolds numbers based on the characteristic length of the microchannel were in the O (1). It is worth noting that for such laminar flows confocal particle image velocimetry can be successfully applied. In this present study, the Reynolds numbers were in the O (100), rendering confocal mPIV impractical and making Micro Particle Image Velocimetry (mPIV) a clear choice.

An Experimental Investigation of the Permeability in Porous Chip Formed by Micropost Arrays Based on Microparticle Image Velocimetry and Micromanometer Measurements

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Haoli Wang ◽  
Pengwei Wang
Keyword(s):  
Cross Section ◽  
Particle Image ◽  
Brinkman Equation ◽  
Two Dimensional ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv ◽  
Image Velocimetry ◽  
Measurement Results ◽  
Microparticle Image Velocimetry ◽  
The Cross

Measurements of velocity and pressure differences for flows in porous chip fabricated with micropost arrays arranged in square pattern were implemented by using micro-particle image velocimetry (micro-PIV) and high precision micromanometer. Based on the measurement results, the permeability was solved by Brinkman equation under the averaged velocities over the cross section, two-dimensional velocities on the center plane of the microchannels, and the averaged velocities on the center plane considering the effect of depth of correlation (DOC), respectively. The experimental results indicate that the nondimensional permeability based on different velocities satisfies the Kozeny–Carman (KC) equation. The Kozeny factor is taken as 40 for the averaged velocity over the cross section and 15 for two kinds of center velocities based on the micropost array of this study, respectively. The permeability calculated by the velocities on the center plane is greater than that by the averaged velocity over the cross section.

Entrance Length Characteristics in Microchannels Using Micro-Particle Image Velocimetry

2007 ◽  
Author(s):  
Tariq Ahmad ◽  
Ibrahim Hassan ◽  
Roland Muwanga
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Working Fluid ◽  
Entrance Length ◽  
Number Range ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv ◽  
Aspect Ratios ◽  
Image Velocimetry

An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of micro-Particle Image Velocimetry (micro-PIV), a non-intrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data is obtained for two different microchannel hydraulic diameters of 500 μm and 100 μm, both of which have cross-sectional aspect ratios of one. The working fluid is distilled water, and velocity profile data is acquired over a laminar Reynolds number range from 0 to 200. The test sections were designed as to provide a sharpedged microchannel inlet from an infinitely sized reservoir, at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100, to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier-Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts, and no influence of scaling was observed.

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