Mixing Enhancement in Spiral Microchannels

2016 ◽  
Author(s):  
Lakshmi Balasubramaniam ◽  
Rerngchai Arayanarakool ◽  
Samuel D. Marshall ◽  
Bing Li ◽  
Poh Seng Lee ◽  
...  
Keyword(s):  
Industrial Applications ◽  
Secondary Flows ◽  
Experimental Investigations ◽  
Mixing Enhancement ◽  
Curved Channel ◽  
Cross Sectional ◽  
Mixing Performance ◽  
Dean Vortices ◽  
Potential Applications ◽  
Sectional Shape

Advancements in the field of microfluidics has led to an increasing interest to study laminar flow in microchannel and its potential applications. Understanding mixing at a microscale can be useful in various biological, heating and industrial applications due to the space and time reduction that micro mixing permits. This work aims to study mixing enhancement due to curved microchannel and the influence of varying microchannel cross sectional shape through numerical and experimental investigations. Unlike prior studies which use channel dimensions in the lower microscale range, this work has been conducted on channels with dimensions in the higher end of micrometer range. Using a cross sectional hydraulic diameter of 600 μm enables introduction of flow into the curved channel at a Reynolds Number ranging from 0.15 to 75, the findings of which show considerable improvement in the mixing performance as compared to that of equivalent straight channels, due to the development of secondary flows known as Dean Vortices.

scholarly journals Current Advances in Ejector Modeling, Experimentation and Applications for Refrigeration and Heat Pumps. Part 2: Two-Phase Ejectors

Inventions ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 16 ◽  
Author(s):  
Zine Aidoun ◽  
Khaled Ameur ◽  
Mehdi Falsafioon ◽  
Messaoud Badache
Keyword(s):  
Heat Pumps ◽  
Operating Conditions ◽  
Industrial Processes ◽  
Experimental Investigations ◽  
Mixing Enhancement ◽  
Data Generation ◽  
Two Phase ◽  
Wide Range ◽  
Potential Applications ◽  
And Performance

Two-phase ejectors play a major role as refrigerant expansion devices in vapor compression systems and can find potential applications in many other industrial processes. As a result, they have become a focus of attention for the last few decades from the scientific community, not only for the expansion work recovery in a wide range of refrigeration and heat pump cycles but also in industrial processes as entrainment and mixing enhancement agents. This review provides relevant findings and trends, characterizing the design, operation and performance of the two-phase ejector as a component. Effects of geometry, operating conditions and the main developments in terms of theoretical and experimental approaches, rating methods and applications are discussed in detail. Ejector expansion refrigeration cycles (EERC) as well as the related theoretical and experimental research are reported. New and other relevant cycle combinations proposed in the recent literature are organized under theoretical and experimental headings by refrigerant types and/or by chronology whenever appropriate and systematically commented. This review brings out the fact that theoretical ejector and cycle studies outnumber experimental investigations and data generation. More emerging numerical studies of two-phase ejectors are a positive step, which has to be further supported by more validation work.

Experimental Investigation of a Free Round Jet with Dean Vortices

2014 ◽  
Vol 9 (2) ◽  
pp. 128-135
Author(s):  
Maria Litvinenko ◽  
Yuriy Litvinenko ◽  
Grigory Kozlov ◽  
Valentin Vikhorev
Keyword(s):  
Experimental Investigation ◽  
Three Dimensional ◽  
Experimental Investigations ◽  
Acoustic Excitation ◽  
Hot Wire ◽  
Curved Channel ◽  
Mean Velocity ◽  
Round Jet ◽  
Smoke Visualization ◽  
Dean Vortices

Results of the experimental investigations of free round jet with Dean vortices formed in curved channel are presented. Hot-wire anemometry measurements of three-dimensional mean velocity profile were performed, smoke visualization pictures cross and longitudinal sections at nozzle exit and downstream were obtained. The features of jet development at acoustic excitation of 40 Hz are shown

Impact of cross-sectional geometry on mixing performance of spiral microfluidic channels characterized by swirling strength of Dean-vortices

2017 ◽  
Vol 27 (9) ◽  
pp. 095016 ◽  
Author(s):  
Lakshmi Balasubramaniam ◽  
Rerngchai Arayanarakool ◽  
Samuel David Marshall ◽  
Bing Li ◽  
Poh Seng Lee ◽  
...  
Keyword(s):  
Microfluidic Channels ◽  
Cross Sectional ◽  
Mixing Performance ◽  
Dean Vortices ◽  
Swirling Strength

Flow Characteristics in a Curved Rectangular Channel With Variable Cross-Sectional Area

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Avijit Bhunia ◽  
C. L. Chen
Keyword(s):  
Pressure Drop ◽  
Rectangular Channel ◽  
Variable Cross ◽  
Entry And Exit ◽  
Curved Channel ◽  
Dean Number ◽  
Cross Sectional ◽  
Dean Vortices ◽  
Area Expansion ◽  
Expansion Effect

Laminar air flow through a curved rectangular channel with a variable cross-sectional (c/s) area (diverging-converging channel) is computationally investigated. Such a flow passage is formed between the two fin walls of a 90 deg bend curved fin heat sink, used in avionics cooling. Simulations are carried out for two different configurations: (a) a curved channel with long, straight, constant c/s area inlet and outlet sections (entry and exit lengths); and (b) a short, curved channel with no entry and exit lengths. Formation of a complex 3D flow pattern and its evolution in space is studied through numerical flow visualization. Results show that a secondary motion sets in the radial direction of the curved section, which in combination with the axial (bulk) flow leads to the formation of a base vortex. In addition, under certain circumstances the axial and secondary flow separate from multiple locations on the channel walls, creating Dean vortices and separation bubbles. Velocity above which the Dean vortices appear is cast in dimensionless form as the critical Dean number, which is calculated to be 129. Investigation of the friction factor reveals that pressure drop in the channel is governed by both the curvature effect as well as the area expansion effect. For a short curved channel where area expansion effect dominates, pressure drop for developing flow can be even less than that of a straight channel. A comparison with the flow in a constant c/s area, curved channel shows that the variable c/s area channel geometry leads to a lower critical Dean number and friction factor.

Secondary Flow Effects in a Trapizoidal Minichannel Flow System Involving Two Straight Sections Separated by a 180° Bend

2007 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Prandtl Number ◽  
Secondary Flow ◽  
Secondary Flows ◽  
Uniform Heat Flux ◽  
Straight Channel ◽  
Cross Sectional ◽  
Pressure Distributions ◽  
Flow Effects ◽  
Sectional Shape ◽  
Bottom To Top

When the flow in a minichannel passes around a bend, secondary flows can develop which can affect the flow, pressure drop and heat transfer rate in the bend and in the flow upstream and downstream of the bend. In order to investigate these effects in more detail attention has been given to flow in a simple minichannel system in which the flow enters the system with a uniform velocity and temperature and passes through a straight channel that has a length that is 10 times the size of the channel. The flow then passes around a rounded 180° bend. Following the bend, the flow passes down another straight channel which also has a length of 10 times the size of the channel. A uniform heat flux is applied over the entire surface of the channel. The channel has a trapezoidal cross-sectional shape. It has been assumed that the flow is steady and incompressible and that there is no slip at the channel walls. The governing equations have been written in dimensionless form and solved using a commercial finite-element based software package, FIDAP. The solution has the following parameters: the Reynolds number, the Prandtl number, the dimensionless radius of the bend and the ratio of the bottom-to-top widths of the channel. Results will only be presented for a Prandtl number 0.7 for Reynolds numbers of between 10 and 500 for various dimensionless bend radii and various bottom-to-top channel width ratios. The major concern in this work is with the extent of the influence of the secondary flow on the flow in the straight channel sections upstream and downstream of the bend. The effect of the channel shape and of the dimensionless channel corner radius on the pressure distributions and on the dimensionless wall temperature distributions, in the straight channel sections in particular, have been considered.

Microstructure of laser-irradiated, conducting Kapton polyimide

1995 ◽  
Vol 53 ◽  
pp. 502-503
Author(s):  
D. L. Callahan ◽  
Z. Ball ◽  
H. M. Phillips ◽  
R. Sauerbrey
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Transmission Electron Microscopy ◽  
Cross Section ◽  
Film Surface ◽  
Cross Sectional ◽  
General Utility ◽  
Transmission Electron ◽  
Considerable Debate ◽  
Potential Applications

Ultraviolet laser-irradiation can be used to induce an insulator-to-conductor phase transition on the surface of Kapton polyimide. Such structures have potential applications as resistors or conductors for VLSI applications as well as general utility electrodes. Although the percolative nature of the phase transformation has been well-established, there has been little definitive work on the mechanism or extent of transformation. In particular, there has been considerable debate about whether or not the transition is primarily photothermal in nature, as we propose, or photochemical. In this study, cross-sectional optical microscopy and transmission electron microscopy are utilized to characterize the nature of microstructural changes associated with the laser-induced pyrolysis of polyimide.Laser-modified polyimide samples initially 12 μm thick were prepared in cross-section by standard ultramicrotomy. Resulting contraction in parallel to the film surface has led to distortions in apparent magnification. The scale bars shown are calibrated for the direction normal to the film surface only.

On the cross-sectional shape of the cellulose crystallites in the tunicate Halocynthia papillosa

1990 ◽  
Vol 48 (3) ◽  
pp. 566-567
Author(s):  
J.-F. Revol ◽  
Y. Van Daele ◽  
F. Gaill
Keyword(s):  
Contrast Imaging ◽  
Animal Kingdom ◽  
Bright Field ◽  
Field Mode ◽  
Cross Sectional ◽  
Ultrathin Sections ◽  
The Cross ◽  
Sectional Shape ◽  
Valonia Ventricosa ◽  
C Nmr

The only form of cellulose which could unequivocally be ascribed to the animal kingdom is the tunicin that occurs in the tests of the tunicates. Recently, high-resolution solid-state l3C NMR revealed that tunicin belongs to the Iβ form of cellulose as opposed to the Iα form found in Valonia and bacterial celluloses. The high perfection of the tunicin crystallites led us to study its crosssectional shape and to compare it with the shape of those in Valonia ventricosa (V.v.), the goal being to relate the cross-section of cellulose crystallites with the two allomorphs Iα and Iβ.In the present work the source of tunicin was the test of the ascidian Halocvnthia papillosa (H.p.). Diffraction contrast imaging in the bright field mode was applied on ultrathin sections of the V.v. cell wall and H.p. test with cellulose crystallites perpendicular to the plane of the sections. The electron microscope, a Philips 400T, was operated at 120 kV in a low intensity beam condition.

Automated 3D measurement of fiber cross section morphology in handsheets

2012 ◽  
Vol 27 (2) ◽  
pp. 264-269 ◽  
Author(s):  
Christian Lorbach ◽  
Ulrich Hirn ◽  
Johannes Kritzinger ◽  
Wolfgang Bauer
Keyword(s):  
Image Analysis ◽  
Cross Section ◽  
Cross Sections ◽  
Image Plane ◽  
3D Measurement ◽  
Cross Sectional ◽  
Fiber Cross Section ◽  
Fiber Wall ◽  
Sectional Shape ◽  
Cross Section Geometry

Abstract We present a method for 3D measurement of fiber cross sectional morphology from handsheets. An automated procedure is used to acquire 3D datasets of fiber cross sectional images using an automated microtome and light microscopy. The fiber cross section geometry is extracted using digital image analysis. Simple sample preparation and highly automated image acquisition and image analysis are providing an efficient tool to analyze large samples. It is demonstrated that if fibers are tilted towards the image plane the images of fiber cross sections are always larger than the true fiber cross section geometry. In our analysis the tilting angles of the fibers to the image plane are measured. The resulting fiber cross sectional images are distorted to compensate the error due to fiber tilt, restoring the true fiber cross sectional shape. We use an approximated correction, the paper provides error estimates of the approximation. Measurement results for fiber wall thickness, fiber coarseness and fiber collapse are presented for one hardwood and one softwood pulp.

Study of Correctly Expanded Sonic Jet with Air Tabs

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Arun Prasad R ◽  
Thanigaiarasu S ◽  
Sembaruthi M ◽  
Rathakrishnan E
Keyword(s):  
Numerical Study ◽  
Cross Sectional ◽  
Potential Core ◽  
Convergent Nozzle ◽  
Jet Mixing ◽  
Pressure Profiles ◽  
Constant Diameter ◽  
Sonic Jet ◽  
Sectional Shape ◽  
Length Reduction

AbstractThe present numerical study is to understand the effect of air tabs located at the exit of a convergent nozzle on the spreading and mixing characteristics of correctly expanded sonic primary jet. Air tabs used in this study are two secondary jets issuing from constant diameter tubes located diametrically opposite at the periphery of the primary nozzle exit, normal to the primary jet. Two air tabs of Mach numbers 1.0 to 1.4, in steps of 0.1 are considered in this study. The mixing modification caused by air tabs are analysed by considering the mixing of uncontrolled (free) primary jet as a reference. Substantial enhancement in jet mixing is achieved with Mach 1.4 air tabs, which results in 80 % potential core length reduction. The total pressure profiles taken on the plane (YZ) normal to the primary jet axis, at various locations along the primary jet centreline revealed the modification of the jet cross sectional shape by air tabs. The stream-wise vortices and bifurcation of the primary jet caused by air tabs are found to be the mechanism behind the enhanced jet mixing.

Experimental investigation and optimization on field shaper structure parameters in magnetic pulse welding

2021 ◽  
pp. 095440542110148
Author(s):  
Yingzi Chen ◽  
Zhiyuan Yang ◽  
Wenxiong Peng ◽  
Huaiqing Zhang
Keyword(s):  
Magnetic Field ◽  
High Speed ◽  
Light Metal ◽  
Magnetic Pulse ◽  
Cross Sectional ◽  
Magnetic Pulse Welding ◽  
Pulse Welding ◽  
Sectional Shape ◽  
Welding System ◽  
The Magnetic Field

Magnetic pulse welding is a high-speed welding technology, which is suitable for welding light metal materials. In the magnetic pulse welding system, the field shaper can increase the service life of the coil and contribute to concentrating the magnetic field in the welding area. Therefore, optimizing the structure of the field shaper can effectively improve the efficiency of the system. This paper analyzed the influence of cross-sectional shape and inner angle of the field shaper on the ability of concentrating magnetic field via COMSOL software. The structural strength of various field shapers was also analyzed in ABAQUS. Simulation results show that the inner edge of the field shaper directly affects the deformation and welding effect of the tube. So, a new shape of field shaper was proposed and the experimental results prove that the new field shaper has better performance than the conventional field shaper.

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