scholarly journals Inertial focusing in a parallelogram profiled microchannel over a range of aspect ratios

2019 ◽  
Vol 7 (1) ◽  
Author(s):  
Joo Young Kwon ◽  
Dong-Ki Lee ◽  
Jungwoo Kim ◽  
Young Hak Cho
Keyword(s):  
Aspect Ratio ◽  
Cfd Simulation ◽  
Rectangular Cross Section ◽  
Wet Etching ◽  
Pdms Mold ◽  
Rectangular Microchannel ◽  
Inertial Focusing ◽  
Particle Focusing ◽  
Aspect Ratios ◽  
Si Wafer

AbstractIn this study, particle focusing phenomena are studied in parallelogram and rectangular cross-sectioned microchannels of varying aspect ratio. In contrast to prior work the microchannels were fabricated using anisotropic wet etching of a Si wafer, plasma bonding, and self-alignment between the Si channel and the PDMS mold. It is shown that the inertial focusing points of the fabricated microchannels of parallelogram and rectangular cross-section were modified as the aspect ratio of the microchannels changed. The particle focusing points of the parallelogram profiled microchannel are compared with those of the rectangular microchannel through experimental measurements and CFD simulation. It is shown that particles can be efficiently focused and separated at a relatively low Reynolds number using a parallelogram profiled microchannel with a low aspect ratio.

Topology Optimization of Micromachined Structures With the Manufacturing Constraints of KOH Etching of (110) Silicon

2008 ◽  
Author(s):  
Sudarshan Hegde ◽  
G. K. Ananthasuresh
Keyword(s):  
Topology Optimization ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Cost Effective ◽  
Wet Etching ◽  
Minimum Length ◽  
The Cost ◽  
Design Parameterization ◽  
Koh Etching ◽  
Si Wafer

The focus of this paper is on designing useful compliant micro-mechanisms of high-aspect-ratio which can be microfabricated by the cost-effective wet etching of (110) orientation silicon (Si) wafers. Wet etching of (110) Si imposes constraints on the geometry of the realized mechanisms because it allows only etch-through in the form of slots parallel to the wafer’s flat with a certain minimum length. In this paper, we incorporate this constraint in the topology optimization and obtain compliant designs that meet the specifications on the desired motion for given input forces. Using this design technique and wet etching, we show that we can realize high-aspect-ratio compliant micro-mechanisms. For a (110) Si wafer of 250 μm thickness, the minimum length of the etch opening to get a slot is found to be 866 μm. The minimum achievable width of the slot is limited by the resolution of the lithography process and this can be a very small value. This is studied by conducting trials with different mask layouts on a (110) Si wafer. These constraints are taken care of by using a suitable design parameterization rather than by imposing the constraints explicitly. Topology optimization, as is well known, gives designs using only the essential design specifications. In this work, we show that our technique also gives manufacturable mechanism designs along with lithography mask layouts. Some designs obtained are transferred to lithography masks and mechanisms are fabricated on (110) Si wafers.

Secondary Flow and Hydraulic Losses Within Sinuous Conduits of Rectangular Cross Section

1992 ◽  
Vol 114 (4) ◽  
pp. 593-600 ◽  
Author(s):  
Yukimaru Shimizu ◽  
Yoshiki Futaki ◽  
C. Samuel Martin
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Flow Patterns ◽  
Geometric Configuration ◽  
Hydraulic Losses ◽  
Aspect Ratios ◽  
Wide Range ◽  
The Relationship

This paper describes the relationship between hydraulic losses and secondary flow within sinuous conduits with complicated bends. It has been found that the nature of secondary flow present in the bends is quite sensitive to the geometric configuration of the bend and the actual aspect ratio of the conduit section. Indeed, many different secondary flow patterns have been found to exist as the bend geometry is altered. A wide range of experiments has been conducted for various aspect ratios of a rectangular conduit with different curvatures.

scholarly journals Constructal Optimization of Rectangular Microchannel Heat Sink with Porous Medium for Entropy Generation Minimization

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1528
Author(s):  
Wenlong Li ◽  
Zhihui Xie ◽  
Kun Xi ◽  
Shaojun Xia ◽  
Yanlin Ge
Keyword(s):  
Heat Flux ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Heat Sink ◽  
Width Ratio ◽  
Microchannel Heat Sink ◽  
Rectangular Microchannel ◽  
Entropy Generation Minimization ◽  
Aspect Ratios ◽  
Length Width

A model of rectangular microchannel heat sink (MCHS) with porous medium (PM) is developed. Aspect ratio of heat sink (HS) cell and length-width ratio of HS are optimized by numerical simulation method for entropy generation minimization (EGM) according to constructal theory. The effects of inlet Reynolds number (Re) of coolant, heat flux on bottom, porosity and volume proportion of PM on dimensionless entropy generation rate (DEGR) are analyzed. From the results, there are optimal aspect ratios to minimize DEGR. Given the initial condition, DEGR is 33.10% lower than its initial value after the aspect ratio is optimized. With the increase of Re, the optimal aspect ratio declines, and the minimum DEGR drops as well. DEGR gets larger and the optimal aspect ratio remains constant with the increasing of heat flux on bottom. For the different volume proportion of PM, the optimal aspect ratios are diverse, but the minimum DEGR almost stays unchanged. The twice minimized DEGR, which results from aspect ratio and length-width ratio optimized simultaneously, is 10.70% lower than the once minimized DEGR. For a rectangular bottom, a lower DEGR can be reached by choosing the proper direction of fluid flow.

Linear stability of rectangular cavity flows driven by anti-parallel motion of two facing walls

2002 ◽  
Vol 458 ◽  
pp. 153-180 ◽  
Author(s):  
S. ALBENSOEDER ◽  
H. C. KUHLMANN
Keyword(s):  
Aspect Ratio ◽  
Linear Stability ◽  
Cross Section ◽  
Strain Field ◽  
Rectangular Cross Section ◽  
Small Range ◽  
Critical Mode ◽  
Plane Flow ◽  
Aspect Ratios ◽  
The Cross

The flow in an infinite slab of rectangular cross-section is investigated numerically by a finite volume method. Two facing walls which move parallel to each other with the same velocity, but in opposite directions, drive a plane flow in the cross-section of the slab. A linear stability analysis shows that the two-dimensional flow becomes unstable to different modes, depending on the cross-sectional aspect ratio, when the Reynolds number is increased. The critical mode is found to be stationary for all aspect ratios. When the separation of the moving walls is larger than approximately twice the height of the cavity, the basic flow forms two vortices, each close to one of the moving walls. The instability of this flow is of centrifugal type and similar to that in the classical lid-driven cavity problem with a single moving wall. When the moving walls are sufficiently close to each other (aspect ratio less than 2) the two vortices merge and form an elliptically strained vortex. Owing to the dipolar strain this flow becomes unstable through the elliptic instability. When both moving walls are very close, the finite-length plane-Couette flow becomes unstable by a similar elliptic mechanism near both turning zones. The critical mode produces wide streaks reaching far into the cavity. For a small range of aspect ratios near unity the flow consists of a single vortex. Here, the strain field is dominated by a four-fold symmetry. As a result the instability process is analogous to the instability of a Rankine vortex in an quadripolar strain field, resulting from vortex stretching into the four corners of the cavity.

Drying of High Aspect Ratio Structures: A Comparison of Drying Techniques via Electrical Stiction Analysis

2009 ◽  
Vol 145-146 ◽  
pp. 87-90 ◽  
Author(s):  
Antoine Pacco ◽  
Masayuki Wada ◽  
Twan Bearda ◽  
Paul W. Mertens
Keyword(s):  
Aspect Ratio ◽  
Surface Area ◽  
High Aspect Ratio ◽  
Wet Etching ◽  
Large Surface Area ◽  
Defect Inspection ◽  
Feature Size ◽  
Aspect Ratios ◽  
Drying Techniques

Nanostructures with high aspect ratios, HAR, (ratio of height to lateral feature size) are of interest for many applications. One of the immediate advantages is the large surface area of these structures. In the field of DRAM manufacturing for example, the capacitance of cylindrical DRAM capacitors increases linearly with height. Wet etching and drying of these fragile high aspect ratio structures without lateral collapse (stiction) is a big challenge for the fabrication of DRAM capacitors. The problem with HAR structures is stiction during drying [1]. In order to reduce stiction by improvement of drying techniques, a good metric to quantify the occurrence of stiction is needed. However, currently used methods like SEM or brightfield defect inspection are extremely time-consuming.

Aspect Ratio Effect on Adiabatic Two-Phase Flow in Rectangular Microchannels

2009 ◽  
Author(s):  
Chiwoong Choi ◽  
DongIn Yu ◽  
Moohwan Kim
Keyword(s):  
Pressure Drop ◽  
Aspect Ratio ◽  
High Speed ◽  
Two Phase Flow ◽  
Rectangular Cross Section ◽  
Phase Flow ◽  
Long Distance ◽  
Two Phase ◽  
Rectangular Microchannel ◽  
Rectangular Microchannels

Most microscale thermal hydraulic systems have been used rectangular microchannels. In a rectangular microchannel, most important parameter is an aspect ratio. In this study, glass rectangular microchannels were fabricated using MEMS (micro-electro-mechanical system) fabrication techniques with a photosensitive glass. The width of all channels is same to approximately 500 μm and the height of rectangular microchannel was changed. The hydraulic diameters of the rectangular microchannels were 490, 322 and 143 μm. Experiments of adiabatic two-phase flow in the rectangular microchannels were conducted using liquid water and nitrogen gas. Pressure drop was directly measured from embedded pressure ports. And the pressure drop results were compared with correlations. Visualization of flow patterns were achieved with a high-speed camera and a long-distance microscope. Bubble behaviors were analyzed using visualized images based on a unit cell concept. As the aspect ratio decreased, a confinement effect was increased. And the thickness of liquid film in the corner of the rectangular cross section was reduced with the aspect ratio decreased. This result affected all phenomena of two-phase flow in the rectangular microchannels.

Investigation of the Inertial Focusing Behavior in Curved Microfluidic Channels for Different Aspect Ratio

2016 ◽  
Author(s):  
Alireza Setayesh Hagh ◽  
Ali Dinler
Keyword(s):  
Particle Separation ◽  
Microfluidic Channels ◽  
Flow Conditions ◽  
Specific Flow ◽  
Inertial Focusing ◽  
Particle Focusing ◽  
Curved Channels ◽  
Aspect Ratios ◽  
Specific Number ◽  
Significant Attention

Inertial focusing has attracted a significant attention in microfluidics applications in recent years. Inertial focusing occurs only under specific flow conditions at which particles migrate across streamlines to a specific number of equilibrium positions. This behavior is mostly not sensitive to the particle size in straight channels. However, curved channels can allow sized based particle separation. In this study, curved channels with various aspect ratios have been investigated by numerical simulations. Consideration of flow regimes reveals that some conditions establish a high-quality single-particle focusing situation which is characterized by the alignment of particles within a narrow band. The outcomes of our numerical model contribute to the understanding of limitation of particle focusing and particle separation in curved microchannels.

Analysis of mixing performances in microchannel with obstacles of different aspect ratios

2019 ◽  
Vol 233 (5) ◽  
pp. 1045-1051 ◽  
Author(s):  
Bappa Mondal ◽  
Sukumar Pati ◽  
PK Patowari
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Flow Condition ◽  
Schmidt Number ◽  
Mixing Efficiency ◽  
Rectangular Microchannel ◽  
Mixing Performance ◽  
Aspect Ratios ◽  
Flow Through

In this study, the mixing performance and pressure drop characteristics have been numerically analyzed for flow through rectangular microchannel with obstacles in the walls arranged in a staggered manner. Three different aspect ratios (AR) of the obstacles are considered, namely 4:1, 1:1, and 1:4. The effects of aspect ratio of the obstacles on the mixing efficiency and the pressure drop are analyzed and compared with that of the channel without obstacle. The results are presented in terms of Reynolds number (Re) and Schmidt number (Sc) in the following range: 0.2 ≤ Re ≤ 1 and 500 ≤ Sc ≤ 1500. Enhanced mixing efficiency is achieved for the case of microchannel with obstacles and the corresponding pressure drop is also found to be higher. The mixing efficiency as well as the pressure drop is maximum for AR = 1:4 among all the geometries considered in the analysis in same flow condition. Furthermore, for a given configuration of the microchannel the mixing efficiency is governed by the mass Peclet number and, accordingly, the mixing efficiency increases with the decrease in Schmidt number for a given Reynolds number.

scholarly journals Differential Sorting of Microparticles Using Spiral Microchannels with Elliptic Configurations

Micromachines ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 412
Author(s):  
Kaan Erdem ◽  
Vahid Ebrahimpour Ahmadi ◽  
Ali Kosar ◽  
Lütfullah Kuddusi
Keyword(s):  
Cell Sorting ◽  
Microfluidic Channel ◽  
Major Axis ◽  
Label Free ◽  
Flow Rates ◽  
Inertial Focusing ◽  
Size Dependent ◽  
Curved Channels ◽  
Aspect Ratios ◽  
Dependent Cell

Label-free, size-dependent cell-sorting applications based on inertial focusing phenomena have attracted much interest during the last decade. The separation capability heavily depends on the precision of microparticle focusing. In this study, five-loop spiral microchannels with a height of 90 µm and a width of 500 µm are introduced. Unlike their original spiral counterparts, these channels have elliptic configurations of varying initial aspect ratios, namely major axis to minor axis ratios of 3:2, 11:9, 9:11, and 2:3. Accordingly, the curvature of these configurations increases in a curvilinear manner through the channel. The effects of the alternating curvature and channel Reynolds number on the focusing of fluorescent microparticles with sizes of 10 and 20 µm in the prepared suspensions were investigated. At volumetric flow rates between 0.5 and 3.5 mL/min (allowing separation), each channel was tested to collect samples at the designated outlets. Then, these samples were analyzed by counting the particles. These curved channels were capable of separating 20 and 10 µm particles with total yields up to approximately 95% and 90%, respectively. The results exhibited that the level of enrichment and the focusing behavior of the proposed configurations are promising compared to the existing microfluidic channel configurations.

scholarly journals Effects of Steel Fiber Percentage and Aspect Ratios on Fresh and Harden Properties of Ultra-High Performance Fiber

2021 ◽  
Vol 2 (3) ◽  
pp. 501-515
Author(s):  
Rajib Kumar Biswas ◽  
Farabi Bin Ahmed ◽  
Md. Ehsanul Haque ◽  
Afra Anam Provasha ◽  
Zahid Hasan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Aspect Ratio ◽  
High Performance ◽  
Steel Fiber ◽  
Setting Time ◽  
Fiber Reinforced Concrete ◽  
Future Research ◽  
Manufacturing Cost ◽  
Aspect Ratios ◽  
High Performance Fiber

Steel fibers and their aspect ratios are important parameters that have significant influence on the mechanical properties of ultrahigh-performance fiber-reinforced concrete (UHPFRC). Steel fiber dosage also significantly contributes to the initial manufacturing cost of UHPFRC. This study presents a comprehensive literature review of the effects of steel fiber percentages and aspect ratios on the setting time, workability, and mechanical properties of UHPFRC. It was evident that (1) an increase in steel fiber dosage and aspect ratio negatively impacted workability, owing to the interlocking between fibers; (2) compressive strength was positively influenced by the steel fiber dosage and aspect ratio; and (3) a faster loading rate significantly improved the mechanical properties. There were also some shortcomings in the measurement method for setting time. Lastly, this research highlights current issues for future research. The findings of the study are useful for practicing engineers to understand the distinctive characteristics of UHPFRC.

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