scholarly journals The Effects Of Blast Lag In Abrasive Jet Machined Micro-Channel Intersections

2021 ◽  
Author(s):  
Soheil Shafagh
Keyword(s):  
Abrasive Particle ◽  
Substrate Material ◽  
Solid Particles ◽  
Microfluidic Channels ◽  
Channel Networks ◽  
Cross Sectional ◽  
Surface Evolution ◽  
Developed Surface ◽  
Micro Channels ◽  
Micro Machine

Abrasive jet micro-machining (AJM) uses compressed air carrying abrasive solid particles to micro-machine a variety of features into surfaces. If the features are smaller than a few mm, then a patterned erosion-resistant mask is used to protect the substrate material, leaving exposed areas to define the features. Previous investigations have revealed a ‘blast lag’ phenomenon in which, for the same dose of abrasive particles, the etched depth of micro-channels and holes tends to decrease as the features become narrower. Blast lag occurs when using AJM on brittle substrates because of the natural tendency to rapidly form a V-shaped cross-sectional profile which inhibits abrasive particle strikes on the narrow vertex at the feature centerline. In this thesis, for the first time, the blast lag phenomenon is studied when using AJM to machine a network of microfluidic channels. It is found that, in some cases, differences in blast lag occurring at channel intersections and within the channels themselves, can lead to channel networks of non-uniform depth. A previously developed surface evolution model is used to predict the onset of blast lag in the channels and intersections, and thus explain these differences. Finally, methods to eliminate the differences are discussed.

scholarly journals The Effects Of Blast Lag In Abrasive Jet Machined Micro-Channel Intersections

2021 ◽  
Author(s):  
Soheil Shafagh
Keyword(s):  
Abrasive Particle ◽  
Substrate Material ◽  
Solid Particles ◽  
Microfluidic Channels ◽  
Channel Networks ◽  
Cross Sectional ◽  
Surface Evolution ◽  
Developed Surface ◽  
Micro Channels ◽  
Micro Machine

Abrasive jet micro-machining (AJM) uses compressed air carrying abrasive solid particles to micro-machine a variety of features into surfaces. If the features are smaller than a few mm, then a patterned erosion-resistant mask is used to protect the substrate material, leaving exposed areas to define the features. Previous investigations have revealed a ‘blast lag’ phenomenon in which, for the same dose of abrasive particles, the etched depth of micro-channels and holes tends to decrease as the features become narrower. Blast lag occurs when using AJM on brittle substrates because of the natural tendency to rapidly form a V-shaped cross-sectional profile which inhibits abrasive particle strikes on the narrow vertex at the feature centerline. In this thesis, for the first time, the blast lag phenomenon is studied when using AJM to machine a network of microfluidic channels. It is found that, in some cases, differences in blast lag occurring at channel intersections and within the channels themselves, can lead to channel networks of non-uniform depth. A previously developed surface evolution model is used to predict the onset of blast lag in the channels and intersections, and thus explain these differences. Finally, methods to eliminate the differences are discussed.

scholarly journals Sculpting Desired Topographies Using Abrasive Jet Micro-Machining

2021 ◽  
Author(s):  
Mohammadreza Sookhaklari
Keyword(s):  
Process Parameters ◽  
High Speed ◽  
Target Material ◽  
Mathematical Framework ◽  
Direct Writing ◽  
Constant Depth ◽  
Cross Sectional ◽  
Surface Evolution ◽  
Micro Channels ◽  
A New Technique

Abrasive jet micromachining (AJM) uses a jet of high-speed particles to erode a wide variety of materials. Given a set of process parameters, surface evolution models capable of predicting the shape of straight, constant-depth channels in a wide variety of materials are well-established. This dissertation presents novel methods for solving the unaddressed more challenging and industrially relevant inverse problem of determining the process parameters required to machine a particular user-specified feature topography. Since the air driven jet used in AJM is divergent, the edges of the desired features are usually defined using a mask which is attached to the surface of the target material. This dissertation presents alternate techniques using stationary or moving shadow masks that can be moved over the surface and maskless techniques, in order to allow direct writing of desired features on the surface. A mathematical framework is then introduced to determine the direct writing source velocity function and path required to create a desired shallow topography. It is also shown how the methodology can be used with existing surface evolution models to predict the feature shape at any depth. The methodologies are demonstrated to work well for the AJM of constant depth micro-channels with user-specified cross-sectional shape, gradient etched micro-channels with specified texture along their length, and pockets with texture in two perpendicular directions. Finally, a new technique is introduced that utilizes a rotating patterned mask in order to control the AJM erosive footprint size and shape. Models for predicting the rotating mask pattern required to create virtually any desired footprint are presented, and experimentally verified for symmetric and asymmetric W-shaped, trapezoidal and wedge shaped footprints.

scholarly journals A Newtonian approach to predict the parameters required to machine high aspect ratio channels of prescribed topography

2021 ◽  
Author(s):  
Aria Ghazavi
Keyword(s):  
Aspect Ratio ◽  
Borosilicate Glass ◽  
High Aspect Ratio ◽  
Traverse Speed ◽  
Cross Sectional ◽  
Average Accuracy ◽  
Micro Channels ◽  
Micro Features ◽  
Micro Machine ◽  
Sectional Shape

Control of the microchannels’ cross-sectional shape may be of interest in micro-heat sinks, microfluidic particle sorting, and micro-machine lubrication applications. Previously, inverse methods have been used to determine the abrasive jet micromachining (AJM) traverse speed and path required to sculpt the desired cross-section for low Aspect Ratio (AR, the ratio of depth to width, see page xiv) topographies (<0.06). This thesisintroduces an iterative inverse method which allows prediction of the machining procedure required to sculpt high AR (>0.06-1) microchannels of prescribed cross-sectional shape using mask-less AJM. The predictions were experimentally verified for trapezoidal and semi-circular micro-channels and protruded features in borosilicate glass, and symmetric and non-symmetric wedges in poly-methyl-methacrylate (PMMA). Overall, the average accuracy of the machined profiles was 93.6 % in borosilicate glass and 91 % in PMMA. The methodology opens up new possibilities for the micro-fabrication of high-aspect-ratio micro-features of virtually any desired shape.

Hydrodynamic Scaling Approaches for the Biomimetic Design of Microfluidic Channels

2006 ◽  
Author(s):  
David R. Emerson ◽  
Krzysztof Cies´licki ◽  
Robert W. Barber
Keyword(s):  
Shear Stress ◽  
Fluid Dynamic ◽  
Design Rule ◽  
Microfluidic Channels ◽  
Cross Sectional ◽  
Biomimetic Design ◽  
Murray's Law ◽  
Hydrodynamic Scaling ◽  
Murray’S Law ◽  
Micro Channels

It is now possible to fabricate networks of micro-channels that mimic the bifurcating structures found in biological vasculatures. The optimum ratio between the diameters of the parent and daughter branches in biological vascular systems can be described by Murray’s law. If the network consists of symmetric bifurcations, an important consequence of Murray’s law is that the tangential shear stress at the wall will remain constant throughout successive generations. This important hydrodynamic concept can be used to provide the basis for developing simple but elegant biomimetic design rules that can be applied to microfluidic networks with arbitrary cross-sectional geometries. The present paper shows how biomimetic networks of constant-depth rectangular and trapezoidal channels can be fabricated using standard photolithographic techniques. The design rule employed is based on the mean shear stress and is used to predict and control the stress distribution within the hierarchical network. The validation of the biomimetic design rule is obtained through a comprehensive series of computational fluid dynamic studies. A range of alternative biomimetic and hydrodynamic scaling principles are also discussed, including power and Reynolds number, that enable different parameters to be controlled in each successive generation.

scholarly journals A Newtonian approach to predict the parameters required to machine high aspect ratio channels of prescribed topography

2021 ◽  
Author(s):  
Aria Ghazavi
Keyword(s):  
Aspect Ratio ◽  
Borosilicate Glass ◽  
High Aspect Ratio ◽  
Traverse Speed ◽  
Cross Sectional ◽  
Average Accuracy ◽  
Micro Channels ◽  
Micro Features ◽  
Micro Machine ◽  
Sectional Shape

Control of the microchannels’ cross-sectional shape may be of interest in micro-heat sinks, microfluidic particle sorting, and micro-machine lubrication applications. Previously, inverse methods have been used to determine the abrasive jet micromachining (AJM) traverse speed and path required to sculpt the desired cross-section for low Aspect Ratio (AR, the ratio of depth to width, see page xiv) topographies (<0.06). This thesisintroduces an iterative inverse method which allows prediction of the machining procedure required to sculpt high AR (>0.06-1) microchannels of prescribed cross-sectional shape using mask-less AJM. The predictions were experimentally verified for trapezoidal and semi-circular micro-channels and protruded features in borosilicate glass, and symmetric and non-symmetric wedges in poly-methyl-methacrylate (PMMA). Overall, the average accuracy of the machined profiles was 93.6 % in borosilicate glass and 91 % in PMMA. The methodology opens up new possibilities for the micro-fabrication of high-aspect-ratio micro-features of virtually any desired shape.

scholarly journals Sculpting Desired Topographies Using Abrasive Jet Micro-Machining

2021 ◽  
Author(s):  
Mohammadreza Sookhaklari
Keyword(s):  
Process Parameters ◽  
High Speed ◽  
Target Material ◽  
Mathematical Framework ◽  
Direct Writing ◽  
Constant Depth ◽  
Cross Sectional ◽  
Surface Evolution ◽  
Micro Channels ◽  
A New Technique

Abrasive jet micromachining (AJM) uses a jet of high-speed particles to erode a wide variety of materials. Given a set of process parameters, surface evolution models capable of predicting the shape of straight, constant-depth channels in a wide variety of materials are well-established. This dissertation presents novel methods for solving the unaddressed more challenging and industrially relevant inverse problem of determining the process parameters required to machine a particular user-specified feature topography. Since the air driven jet used in AJM is divergent, the edges of the desired features are usually defined using a mask which is attached to the surface of the target material. This dissertation presents alternate techniques using stationary or moving shadow masks that can be moved over the surface and maskless techniques, in order to allow direct writing of desired features on the surface. A mathematical framework is then introduced to determine the direct writing source velocity function and path required to create a desired shallow topography. It is also shown how the methodology can be used with existing surface evolution models to predict the feature shape at any depth. The methodologies are demonstrated to work well for the AJM of constant depth micro-channels with user-specified cross-sectional shape, gradient etched micro-channels with specified texture along their length, and pockets with texture in two perpendicular directions. Finally, a new technique is introduced that utilizes a rotating patterned mask in order to control the AJM erosive footprint size and shape. Models for predicting the rotating mask pattern required to create virtually any desired footprint are presented, and experimentally verified for symmetric and asymmetric W-shaped, trapezoidal and wedge shaped footprints.

scholarly journals Electromagnetic Stirring versus ECAP: Morphological Comparison of Al-Si-Cu Alloys to Make the Microstructural Refinement for Use in SSM Processing

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Luis Vanderlei Torres ◽  
Luis Fernando Torres ◽  
Eugênio José Zoqui
Keyword(s):  
Equal Channel Angular Pressing ◽  
Morphological Evolution ◽  
Direct Chill ◽  
Solid Particles ◽  
Electromagnetic Stirring ◽  
Semisolid State ◽  
Morphological Comparison ◽  
Globular Structure ◽  
Cross Sectional ◽  
Angular Pressing

This work evaluates the morphological evolution at the semisolid state of the Al-4.0wt%Si-2.5wt%Cu alloy produced by direct chill casting under electromagnetic stirring (EMS) and by one equal channel angular pressing (ECAP) pass. The ECAP emerged as a promising technique capable of reduction and homogeneous metals microstructure imposing large deformations occurs in a matrix that contains two channels of the same cross-sectional area and forms an angle of 120°. The materials were submitted to reheating treatment in condition of 60% solid fraction at treatment times of 0, 30, and 90 s. Comparing the two cases, we have the presented ECAP process that had an excellent response to the recovery and recrystallization mechanisms, and refined microstructures ideal for thixoforming were produced. Primary particle sizes of about 45 μm and grain sizes of about 75 μm and a circularity shape factor of more than 0.60 were obtained. The low silicon alloy, Al-4.0wt%Si-2.5wt%Cu, presented excellent refinement when processed via equal channel angular pressing, presenting good morphological stability at the semisolid state, without significant changes in size or shape of the solid particles. This fully globular structure is favourable for thixoforming processes.

Mechanism Research on the Swirling Air Flow Compounded with Magnetic-Field Finishing

2008 ◽  
Vol 53-54 ◽  
pp. 51-55 ◽  
Author(s):  
Xiu Hong Li ◽  
Shi Chun Yang
Keyword(s):  
Magnetic Field ◽  
Surface Roughness ◽  
Air Flow ◽  
Abrasive Particle ◽  
Solid Particles ◽  
Two Phase ◽  
Machining Time ◽  
Machined Surface ◽  
Magnetic Field Coupling ◽  
Swirling Air Flow

A new finishing technology of the swirling air flow compounded with magnetic-field is advanced. Force acting on abrasive is analyzed by the action of airstream and magnetic-field coupling according to gas-solid particles two-phase flow. Finishing mechanism on the swirling air flow compounded with magnetic-field is illustrated, namely, burrs and microcosmic peak on the surface of workpiece are broken, grinded and cut via a great deal of abrasive particle impacting, microchipping and rolling machined surface. Unthreaded hole is experimented on the condition of changing magnetic induction intensity B and machining time t. Changing curve of surface roughness Ra along with time t is shown. Research indicates that machining time of the swirling air flow compounded with magnetic-field is short and machining efficiency is high. The longer machining time is, the smaller surface roughness Ra is and the better machining effect is.

Comparative Study of Effective Cooling in Microchannel Heat Sinks (MCHS) With Nanofluid and Hydrophobic Nanostructures Using Computational Fluid Dynamics

2020 ◽  
Author(s):  
Darryl Jennings ◽  
Sonya Smith
Keyword(s):  
Pressure Drop ◽  
Analytical Model ◽  
Convection Heat Transfer ◽  
Flow Characteristics ◽  
Heat Sinks ◽  
Cross Sectional ◽  
Ansys Fluent ◽  
Cooling Flow ◽  
Micro Channels ◽  
The Impact

Abstract The goal of this research is to present an analytical model of nanostructures and study the effects of their geometry on the performance of micro channels. The pressure drop experienced by micro channels is of interest as it presents a limit on forced convection heat transfer. This work will demonstrate how the presence of nanostructures primarily affects pressure drop as well as other cooling flow characteristics. Additional work in the impact of microchannel cross-sectional geometry and friction factor formulation is provided as well. Multiple transient analyses were performed in ANSYS FLUENT to ascertain performance characteristics of microchannels without the presence of hydrophobic nanostructures. The results were compared to the analytical model developed in this study.

Heat Transfer Enhancement in Wavy Micro-Channels Through Multiharmonic Surfaces

2018 ◽  
Author(s):  
Justin Moon ◽  
J. Rafael Pacheco ◽  
Arturo Pacheco-Vega
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Numerical Solutions ◽  
Cold Water ◽  
Bottom Surface ◽  
Transfer Enhancement ◽  
Cross Sectional ◽  
Single Wave ◽  
Micro Channels

In this study, three-dimensional numerical simulations are performed to investigate heat transfer enhancement in multi-harmonic micro-scale wavy channels. The focus is on the influence of channel surface-topography, modeled as multi-harmonic sinusoidal waves of square cross-sectional area, on the enhancing mechanisms. A single-wave device of 0.5 mm × 0.5 mm × 20 mm length, is used as baseline, and new designs are built with harmonic-type surfaces. The channel is enclosed by a solid block, with the bottom surface within the sinusoidal region being exposed to a 47 W/cm2 heat flux. The numerical solutions of the governing equations for an incompressible laminar flow and conjugate heat transfer are obtained via finite elements. By using the ratio of the Nusselt number for wavy to straight channels, a parametric analysis — for a set of cold-water flowrates (Re = 50, 100, and 150) — shows that the addition of harmonic surfaces enhances the transfer of energy and that such ratio achieves the highest value with wave harmonic numbers of n = ±2. Use of a performance factor (PF), defined as the ratio of the Nusselt number to the pressure drop, shows that, surprisingly, the proposed wavy multi-harmonic channels are not as efficient as the single-wave geometries. This outcome is thought to be, primarily, due to the uncertainty associated with the definition of the Nusselt number used in this study, and establishes a direction to investigate the development of a more accurate definition.

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