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 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.

Influences of Cross-Sectional Geometry and Surface Roughness on the Compression Stability in Upsetting High Aspect-Ratio Shaped Billets by FE Analysis

2006 ◽  
Author(s):  
Yuan-Chuan Hsu ◽  
Heng-Sheng Lin ◽  
Tung-Sheng Yang
Keyword(s):  
Surface Roughness ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Metal Forming ◽  
Fe Analysis ◽  
Cross Sectional ◽  
Shape Factors ◽  
Element Simulation ◽  
Billet Cross Section ◽  
Sectional Shape

Metal forming for micro or mini-parts is a new developing trend in the metal forming application. The analysis of billet compression stability in upsetting is essential in selecting forming parameters and determining the size effect. The current study aims to explore the influence of billet geometry and surface roughness on the compression stability in upsetting high aspect-ratio shaped billets. 3D finite element simulation was employed to analyze the influence of surface roughness on the end faces of the billet and shapes profiles of the billet cross-section, on buckling in upsetting mini-size billets. Simulation results indicated that the rougher the contact surface, the lower was compression stability in upsetting the billets. In addition, the cross-sectional shape of the billet affected the compression stability in upsetting. Mini billets with larger shape factors would lead to higher compression stability.

Optimized High-Aspect-Ratio Diffusional Micromixers

2008 ◽  
Author(s):  
Amit Maha ◽  
Vamsidhar Palaparthy ◽  
Steven A. Soper ◽  
Michael C. Murphy ◽  
Dimitris E. Nikitopoulos
Keyword(s):  
Pressure Drop ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Optimization Procedure ◽  
Main Stream ◽  
Total Production ◽  
Production Time ◽  
Operating Condition ◽  
Micro Channels ◽  
Mixture Volume

This part of our work has been aimed at designing, manufacturing and characterizing effective micro-mixers which are cheap, durable and easily integrated on a variety of bio-chips with emphasis on those performing Polymerese Chain Reactions (PCR) and Ligase Detection Reactions (LDR). A key contribution is the development of an optimization procedure for the design of passive micro-mixers utilizing high-aspect-ratio micro-channels (HARMC). The optimization procedure identifies the optimum type of mixer on the basis of the flow rate proportions of the mixture constituents and provides for two optimum designs of the selected mixer type for an aspect ratio of choice in two ways: (a) for specified mixture volume and mixer pressure drop the optimum mixer dimensions and operating condition minimize the total production time and (b) for specified mixture volume and a total production time the optimum mixer dimensions and operating condition minimize the mixer pressure drop. The simplest and easiest to manufacture layout of an optimized mixer configuration (X2JC) with two inlet ports and three layers is shown in Figure 1. The injection of compound 1 into the compound 2 main stream is performed through two side-jets in a wider channel to further reduce the pressure loss overhead followed by a contraction into the main mixing channel.

Computational Fluid Dynamic Modelling of High Aspect Ratio Cross-Sectional Jets I: The Effect of Orifice Shape on Jet Behaviour

2003 ◽  
Author(s):  
Sarah J. Wakes
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Dynamic Modelling ◽  
Common Belief ◽  
Cross Sectional ◽  
Numerical Work ◽  
Hydrocarbon Production ◽  
Gas Dispersion

High aspect ratio cross-sectional jets (HAR jets) are significant for many industrial applications including offshore hydrocarbon production safety, manufacturing processes, aeronautics and others. Little interest has been paid to such jets as the common belief was that within an acceptable distance from the jet orifice the behaviour emulates that of an axisymmetric jet. Previous experimental and preliminary numerical work [1–4] has shown that this is not necessarily correct. Work has been done to investigate numerically the effect the orifice shape has on the behaviour of the jets. This will be in terms of the curvature of the orifice in comparison to the same aspect ratio with a straight rectangular shape. Simulations have been carried out relating to experimental work [1] as comparison and verification. The spreading of the jet will be assessed as it can have significance in terms of safety, performance and effectiveness. This work enhances previous work [3] and allows an assessment of whether such a curvature in the inlet significantly effects the jet behaviour for two pipe pressures. The choice of turbulence model will also be assessed in terms of the standard two-equation k-ε model and it’s variants the RNG and Realisable models. Later work will investigate the use of Large Eddy Simulation within the context of the geometry used here. This important information will allow for greater understanding for the modelling of such jets in a CFD simulation within a complex industrial problem such as gas dispersion with a hydrocarbon production area. It is realized that the fluid does not emerge as a single velocity from the pipe into the flange and hence to form the inlet for the jet. Therefore the effect of the flow within the pipe and how this effects the emerging jet behaviour is investigated in part II of this paper [5].

Evaporating Meniscus of Ethanol and Ethanol-Based Nanofluids in Single Micro-Channels

2013 ◽  
Vol 390 ◽  
pp. 685-690
Author(s):  
Yuan Wang ◽  
Khellil Sefiane ◽  
Zhen Guo Wang
Keyword(s):  
Heat Flux ◽  
Aspect Ratio ◽  
Evaporation Rate ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Particle Volume ◽  
Cross Sectional ◽  
Stick Slip ◽  
Micro Channels ◽  
Sink Effect

Evaporating meniscus of ethanol and ethanol-based nanofluids (0.01vol.%) in micro-channels were experimentally studied. Visualisation and thermographic results of the stationary meniscus confined in high-aspect-ratio rectangular micro-channels (hydraulic diameters are 571 μm, 727 μm and 1454 μm, channel cross sectional aspect ratio is 20, 20, 10 respectively) were obtained. It was found that interface evaporation rate increases with heat flux. The meniscus interface becomes deformed when the evaporation rate increases. The use of nanofluids largely enhances the interface stability even though the particle volume fraction is at a very low level. Besides, a stick-slip and back-jump behaviour of the nanofluids meniscus was captured during the transition from stable to deformed interface. Moreover, sink effect at the liquid-vapour interface was discussed based on the IR results.

Modelling the Acoustical and Airflow Performance of Simple Lined Ventilation Apertures

2005 ◽  
Vol 12 (4) ◽  
pp. 277-292 ◽  
Author(s):  
D J Oldham ◽  
Jian Kang ◽  
M W Brocklesby
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
High Aspect Ratio ◽  
Natural Ventilation ◽  
Ventilation System ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Ventilation Performance ◽  
Acoustic Treatment

The pressure differences that can be used to drive a natural ventilation system are very small and thus large apertures are required to allow sufficient air to enter and leave a building to ensure good air quality or thermal comfort. Large apertures are potential acoustic weak points on a façade and may require some form of acoustic treatment such as absorbent linings, in which case the ventilator is similar to a short section of lined duct. In ducts, the performance of absorbent linings increases with the length of lining and the ratio of the length of lined perimeter to the cross sectional area of the duct. Thus, for a duct of a given cross sectional area, a lining is more effective for a duct with a high aspect ratio than for a duct with a square cross section. However, the high aspect ratio cross section will result in greater flow resistance and impede the airflow performance. In this paper numerical methods are employed to investigate the effect of different configurations of a lined aperture on the acoustical and ventilation performance of the aperture in order to establish the optimum configurations.

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.

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