scholarly journals Hydrodynamic particle focusing enhanced by femtosecond laser deep grooving at low Reynolds numbers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tianlong Zhang ◽  
Misuzu Namoto ◽  
Kazunori Okano ◽  
Eri Akita ◽  
Norihiro Teranishi ◽  
...  
Keyword(s):  
Flow Rate ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Flow ◽  
Live Cells ◽  
Low Reynolds Numbers ◽  
Particle Focusing ◽  
Human T Cell ◽  
Fs Laser ◽  
Low Reynolds

AbstractMicrofluidic focusing of particles (both synthetic and biological), which enables precise control over the positions of particles in a tightly focused stream, is a prerequisite step for the downstream processing, such as detection, trapping and separation. In this study, we propose a novel hydrodynamic focusing method by taking advantage of open v-shaped microstructures on a glass substrate engraved by femtosecond pulse (fs) laser. The fs laser engraved microstructures were capable of focusing polystyrene particles and live cells in rectangular microchannels at relatively low Reynolds numbers (Re). Numerical simulations were performed to explain the mechanisms of particle focusing and experiments were carried out to investigate the effects of groove depth, groove number and flow rate on the performance of the groove-embedded microchannel for particle focusing. We found out that 10-µm polystyrene particles are directed toward the channel center under the effects of the groove-induced secondary flows in low-Re flows, e.g. Re < 1. Moreover, we achieved continuous focusing of live cells with different sizes ranging from 10 to 15 µm, i.e. human T-cell lymphoma Jurkat cells, rat adrenal pheochromocytoma PC12 cells and dog kidney MDCK cells. The glass grooves fabricated by fs laser are expected to be integrated with on-chip detection components, such as contact imaging and fluorescence lifetime-resolved imaging, for various biological and biomedical applications, where particle focusing at a relatively low flow rate is desirable.

Experimental characterization of three-dimensional corner flows at low Reynolds numbers

2012 ◽  
Vol 707 ◽  
pp. 37-52 ◽  
Author(s):  
J. Sznitman ◽  
L. Guglielmini ◽  
D. Clifton ◽  
D. Scobee ◽  
H. A. Stone ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Cross Section ◽  
Experimental Characterization ◽  
Low Reynolds Numbers ◽  
Low Reynolds

AbstractWe investigate experimentally the characteristics of the flow field that develops at low Reynolds numbers ($\mathit{Re}\ll 1$) around a sharp $9{0}^{\ensuremath{\circ} } $ corner bounded by channel walls. Two-dimensional planar velocity fields are obtained using particle image velocimetry (PIV) conducted in a towing tank filled with a silicone oil of high viscosity. We find that, in the vicinity of the corner, the steady-state flow patterns bear the signature of a three-dimensional secondary flow, characterized by counter-rotating pairs of streamwise vortical structures and identified by the presence of non-vanishing transverse velocities (${u}_{z} $). These results are compared to numerical solutions of the incompressible flow as well as to predictions obtained, for a similar geometry, from an asymptotic expansion solution (Guglielmini et al., J. Fluid Mech., vol. 668, 2011, pp. 33–57). Furthermore, we discuss the influence of both Reynolds number and aspect ratio of the channel cross-section on the resulting secondary flows. This work represents, to the best of our knowledge, the first experimental characterization of the three-dimensional flow features arising in a pressure-driven flow near a corner at low Reynolds number.

Low Reynolds-Number Experiments in an Axial-Flow Turbomachine

1964 ◽  
Vol 86 (3) ◽  
pp. 257-295 ◽  
Author(s):  
J. Neustein
Keyword(s):  
Reynolds Number ◽  
Guide Vane ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Low Flow ◽  
Working Fluid ◽  
Low Reynolds Numbers ◽  
Blade Row ◽  
Overall Performance ◽  
Low Reynolds

The performance of a single-stage, axial-flow turbomachine was studied experimentally at low Reynolds numbers. The study was made with a turbomachine modeled from a large jet-engine type of axial-flow compressor. Low Reynolds numbers were obtained by using a mixture of glycerine and water as the working fluid. The overall performance was determined over a range of Reynolds numbers RT (based on rotor-tip speed and rotor chord) from 2000 to 150,000. The flow rate at each Reynolds number was varied from near shutoff to the maximum permitted by the turbomachine-tunnel systems. Blade-row characteristics were studied by means of quantitative flow surveys before and after each blade row, and by means of extensive flow-visualization experiments within each blade row. The investigation established that sudden or critical changes in performance do not occur in the type of machine tested, between RT of 150,000 and 20,000. Below 20,000 the performance deteriorated more rapidly. A relatively sharp change in performance occurred between RT of 20,000 and 10,000. The results clarified many of the viscous flow details in each blade row which are associated with the deterioration of performance. These effects were very pronounced at RT of 4000 and below. Consequently, a considerable part of the paper is concerned with results obtained at these lower Reynolds numbers. From the point of view of a designer, information is presented in regard to overall performance, guide-vane turning, and guide-vane and stator total-pressure losses, all as functions of Reynolds number. These results are expected to be indicative of performance in turbomachines similar to the one tested here. Other details are concerned with problems such as wall boundary layers, flow reversal at low flow coefficients, lip-clearance flow, flow patterns near shutoff, and flow comparisons in stators with rotating and stationary hubs.

An Electrokinetic Micro Mixer for Lab-on-Chip Applications: Modeling, Validation, and Optimization

2011 ◽  
Author(s):  
Hendryk Bockelmann ◽  
Vincent Heuveline ◽  
Peter Ehrhard ◽  
Dominik P. J. Barz
Keyword(s):  
Electrical Potential ◽  
Reynolds Numbers ◽  
Base Flow ◽  
Secondary Flows ◽  
Electrical Field ◽  
Lab On Chip ◽  
Low Reynolds Numbers ◽  
Micro Particle Image Velocimetry ◽  
Low Reynolds ◽  
Micro Mixer

Mixing of liquids in micro mixers at low Reynolds numbers is a challenging task since the flow regime is laminar and it is difficult to engage instabilities of the flow. In many microfluidic systems, mixing can be improved by means of electrokinetic effects. A favorable micro mixer design consists of a Y-junction, where the different liquid streams merge, and a subsequent meandering microchannel. A pressure gradient pumps the liquids to be mixed through the microchannel. An oscillating electrical field is superimposed onto the pressure-driven base flow which generates an additional electrokinetic (electro osmotic) flow. These oscillating secondary flows in conjunction with the meandering geometry are responsible for stretching and folding of the contact area of the liquids to be mixed which enhances the mass transfer rates considerably. In this contribution, we present a mathematical model which allows for the numerical simulation of flow, electrical potential, and species concentration. The model is validated by experiments relying on Micro Particle Image Velocimetry (μPIV). Consequently, this model can be used to numerically optimize the electrical field in order to achieve fast and high mixing even at low Reynolds numbers.

Novel Low Reynolds Number Mixers for Microfluidic Applications

2003 ◽  
Author(s):  
S. P. Vanka ◽  
C. M. Winkler ◽  
J. Coffman ◽  
E. Linderman ◽  
S. Mahjub ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Rhodamine 6G ◽  
Rectangular Cross Section ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Reynolds Numbers ◽  
Sucrose Solutions ◽  
Low Reynolds ◽  
Rhodamine 6G Dye ◽  
Microfabrication Techniques

We present two new designs of compact mixers that can provide good mixing at low Reynolds numbers encountered in many microfluidic devices. The new designs benefit from curvature induced cross-stream vortices to enhance mixing of two co-flowing streams of fluids arranged side by side. One of the designs is a spiral of rectangular cross-section, while the other is a series of concentric circular channels arranged as a labyrinth. Both utilize the formation of sustained secondary flows to enhance mixing between two streams. Currently, the devices are fabricated in aluminum using standard machining techniques. However, they can be reduced further in size using standard microfabrication techniques. Mixing experiments were conducted in these channels at a Reynolds number of 6.8 using two sucrose solutions, one of which was laced with Rhodamine 6G dye. Compared to a experiment in an equivalent straight channel, a significant enhancement in the mixing of the two streams, as indicated by the intensity of the second fluid’s color, was observed. The present designs provide a compact and easy-to-fabricate alternative to various other concepts proposed in literature.

scholarly journals Effect of the inlet flow rate ratio on liquid efficiency in a T-shaped micromixer at low Reynolds numbers

2020 ◽  
Vol 1677 ◽  
pp. 012138
Author(s):  
A Yu Kravtsova ◽  
M V Kashkarova ◽  
P E Ianko ◽  
A V Bilsky ◽  
Y V Kravtsov
Keyword(s):  
Flow Rate ◽  
Rate Ratio ◽  
Reynolds Numbers ◽  
Flow Rate Ratio ◽  
Inlet Flow ◽  
Low Reynolds Numbers ◽  
Inlet Flow Rate ◽  
Low Reynolds

A Reassessment of Metering Orifices for Low Reynolds Numbers

1965 ◽  
Vol 180 (1) ◽  
pp. 331-356 ◽  
Author(s):  
L. J. Kastner ◽  
J. C. McVeigh
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Flow Rate ◽  
Discharge Coefficient ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
Discharge Coefficients ◽  
Low Reynolds

In view of the importance of accurate measurement of flow rate at low Reynolds numbers, there have been numerous attempts to develop metering devices having constant discharge coefficients in the range of pipe Reynolds numbers between about 3000 and 200 and even below this latter value, and some of these attempts have achieved a reasonable degrees of success. Nevertheless, some confusion exists regarding the dimensions and range of utility of certain designs which have been recommended and further information is necessary in order that the situation may be clarified. The aims of the present investigation, which is believed to be wider in scope than any published in this field in recent years, were to review and correlate existing knowledge and to make an experimental study of the properties of various types of orifice in the low range of Reynolds numbers. Arising from this it was hoped that a design might be evolved which not only had a satisfactorily constant discharge coefficient throughout the range but was also simple to manufacture and reproduce, even for small orifice diameters of the order of 0.5 in or less, and it is believed that some success in attaining this aim was achieved. The first section of the paper contains a review of previous investigations classified into three main groups. In the second part of the paper, experiments with various types of orifice plate are described and it is shown that a properly proportioned single-bevelled orifice has as good a performance in the low Reynolds number range as that of any of the more complicated shapes.

scholarly journals Characteristics of an Annular Turbine Cascade at Low Reynolds Numbers

1998 ◽  
Author(s):  
Takayuki Matsunuma ◽  
Hiroyuki Abe ◽  
Yasukata Tsutsui ◽  
Koji Murata
Keyword(s):  
Reynolds Number ◽  
Gas Turbines ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Aerodynamic Characteristics ◽  
Secondary Flows ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Reynolds

The aerodynamic characteristics of turbine cascades are thought to be relatively satisfactory due to the favorable pressure gradient of the accelerating flow. But within the low Reynolds number region of approximately 6×104 where the 300kW ceramic gas turbines which are being developed under the New Sunshine Project of Japan operate, the characteristics such as boundary layer separation, reattachment and secondary flow which lead to prominent power losses can not be easily predicted. In this research, experiments have been conducted to evaluate the performance of an annular turbine stator cascade. Wakes of the cascade were measured using a single hot wire and five hole pressure tube, for a range of blade chord Reynolds numbers based on the inlet condition from 2×104 to 12×104. Flow visualizations on the suction surface of the blade were carried out using oil film method. At low Reynolds numbers, the flow structure in the annular cascade was quite complex and three-dimensional. The separation line on the suction surface moved upstream due to the decrease of Reynolds number. In addition, the growth of secondary flows, i.e., passage vortices and leakage vortex, was extremely under the influence of Reynolds number.

The Spacer Grid Effect on Heat Transfer at Low Flow Rate in a 5×5 Rod Bundles

2016 ◽  
Author(s):  
Da Liu ◽  
Hanyang Gu ◽  
Shengjie Gong
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
Low Flow ◽  
Transfer Enhancement ◽  
Spacer Grid ◽  
Maximum Enhancement ◽  
Low Reynolds Numbers

It is widely acknowledged that the spacer grid has great effect on heat transfer downstream of it. The conventional correlations to predict the augmentation of the spacer were carried out on high Reynolds numbers. However, recent studies have shown that Reynolds number on the heat transfer enhancement is not negligible when the Reynolds number is lower than about 10000. An experiment to investigate the single-phase convective heat transfer downstream of the spacer grid at low flow rate has been performed in a 5×5 rod bundle. The test section was uniformly heated by a DC power and cooled by water. The Reynolds number covered from about 2000 to 10000. The experiment showed that the existing correlations for heat transfer enhancement by a spacer grid underestimated the maximum enhancement at the grid exit of the spacer grid at low Reynolds numbers. As the Reynolds number decreases, the maximum enhancement increases, nevertheless, when Reynolds number decreases to about 4300, the maximum enhancement tend to converge at a certain value. A new correlation has been proposed to account for the Reynolds number effect on heat transfer enhancement downstream of the spacer grid at low Reynolds numbers and which gave good predictions.

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