scholarly journals Free-Flowing Shear-Thinning Liquid Film in Inclined μ-Channels

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 8 ◽  
Author(s):  
Angeliki Koupa ◽  
Yorgos Stergiou ◽  
Aikaterini Mouza
Keyword(s):  
Liquid Film ◽  
Interfacial Area ◽  
Shear Thinning ◽  
Transfer Rates ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Inclination Angles ◽  
Open Microchannel ◽  
Computational Fluid Dynamics Cfd ◽  
Free Falling

Among the most important variables in the design of falling film microreactors (FFMRs) is the liquid film thickness as well as the gas/liquid interfacial area, which dictate the mass and heat transfer rates. In a previous work conducted in our lab the characteristics of a free-falling Newtonian liquid film have been studied and appropriate correlations have been proposed. In this work the geometrical characteristics of a non-Newtonian shear thinning liquid, flowing in an inclined open microchannel, have been experimentally investigated and design correlations that can predict with reasonable accuracy the features of a FFMR have been proposed. The test section used was an open μ-channel with square cross section (WO = 1200 μm) made of brass which can be set to various inclination angles. The liquid film characteristics were measured by a non-intrusive technique that is based on the features of a micro Particle Image Velocimetry (μ-PIV) system. Relevant computational fluid dynamics (CFD) simulations revealed that the volume average dynamic viscosity over the flow domain is practically the same as the corresponding asymptotic viscosity value, which can thus be used in the proposed design equations. Finally, a generalized algorithm for the design of FFMRs, containing non-Newtonian shear thinning liquids, is suggested.

scholarly journals Free-Flowing Shear-Thinning Liquid Film in Inclined μ-Channels

2018 ◽  
Author(s):  
Angeliki T. Koupa ◽  
Yorgos G. Stergiou ◽  
Aikaterini A. Mouza
Keyword(s):  
Liquid Film ◽  
Interfacial Area ◽  
Shear Thinning ◽  
Falling Film ◽  
Cfd Simulations ◽  
Transfer Rates ◽  
Inclination Angles ◽  
Open Microchannel ◽  
Free Falling ◽  
Film Characteristics

Among the most important variables in the design of falling film microreactors (FFMRs) is the liquid film thickness as well as the gas/liquid interfacial area, which dictate the mass and heat transfer rates. In a previous work conducted in our lab the characteristics of a free-falling Newtonian liquid film have been studied and appropriate correlations have been proposed. In this work the geometrical characteristics of a non-Newtonian shear thinning liquid, flowing in an inclined open microchannel, have been experimentally investigated and design correlations that can predict with reasonable accuracy the features of a FFMR have been proposed. The test section used was an open μ-channel with square cross section (Wo=1200 μm) made of brass which can be set to various inclination angles. The liquid film characteristics were measured by a non-intrusive technique that is based on the features of a μ-PIV system. Relevant CFD simulations revealed that the volume average dynamic viscosity over the flow domain is practically the same as the corresponding asymptotic viscosity value, which can thus be used in proposed the design equations. Finally, a generalized algorithm for the design of FFMRs, containing non-Newtonian shear thinning liquids, is suggested.

scholarly journals Experimental and Numerical Study of Blood Flow in μ-vessels: Influence of the Fahraeus–Lindqvist Effect

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 143
Author(s):  
Yorgos G. Stergiou ◽  
Aggelos T. Keramydas ◽  
Antonios D. Anastasiou ◽  
Aikaterini A. Mouza ◽  
Spiros V. Paras
Keyword(s):  
Blood Flow ◽  
Axial Velocity ◽  
Particle Image ◽  
Numerical Study ◽  
Implantable Devices ◽  
Cfd Simulations ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Cfd ◽  
Cell Free Layer

The study of hemodynamics is particularly important in medicine and biomedical engineering as it is crucial for the design of new implantable devices and for understanding the mechanism of various diseases related to blood flow. In this study, we experimentally identify the cell free layer (CFL) width, which is the result of the Fahraeus–Lindqvist effect, as well as the axial velocity distribution of blood flow in microvessels. The CFL extent was determined using microscopic photography, while the blood velocity was measured by micro-particle image velocimetry (μ-PIV). Based on the experimental results, we formulated a correlation for the prediction of the CFL width in small caliber (D < 300 μm) vessels as a function of a modified Reynolds number (Re∞) and the hematocrit (Hct). This correlation along with the lateral distribution of blood viscosity were used as input to a “two-regions” computational model. The reliability of the code was checked by comparing the experimentally obtained axial velocity profiles with those calculated by the computational fluid dynamics (CFD) simulations. We propose a methodology for calculating the friction loses during blood flow in μ-vessels, where the Fahraeus–Lindqvist effect plays a prominent role, and show that the pressure drop may be overestimated by 80% to 150% if the CFL is neglected.

scholarly journals Validation of a CFD Methodology for Positive Displacement LVAD Analysis Using PIV Data

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Richard B. Medvitz ◽  
Varun Reddy ◽  
Steve Deutsch ◽  
Keefe B. Manning ◽  
Eric G. Paterson
Keyword(s):  
Left Ventricular ◽  
Hydrodynamic Performance ◽  
Ventricular Assist ◽  
Shear Rates ◽  
Eddy Simulation ◽  
Positive Displacement ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Cfd ◽  
High Level

Computational fluid dynamics (CFD) is used to asses the hydrodynamic performance of a positive displacement left ventricular assist device. The computational model uses implicit large eddy simulation direct resolution of the chamber compression and modeled valve closure to reproduce the in vitro results. The computations are validated through comparisons with experimental particle image velocimetry (PIV) data. Qualitative comparisons of flow patterns, velocity fields, and wall-shear rates demonstrate a high level of agreement between the computations and experiments. Quantitatively, the PIV and CFD show similar probed velocity histories, closely matching jet velocities and comparable wall-strain rates. Overall, it has been shown that CFD can provide detailed flow field and wall-strain rate data, which is important in evaluating blood pump performance.

Flow Characteristics of Pressure-Driven Water in Serpentine Micro-Channels

2006 ◽  
Author(s):  
Renqiang Xiong ◽  
J. N. Chung
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Flow Structures ◽  
Micro Channel ◽  
Pressure Drops ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Micro Channels ◽  
Shape And Size

Flow structures and pressure drops were investigated in rectangular serpentine micro-channels with miter bends which had hydraulic diameters of 0.209mm, 0.395mm and 0.549mm respectively. To evaluate the bend effect, the additional pressure drop due to the miter bend must be obtained. Three groups of micro-channels were fabricated to remove the inlet and outlet losses. A validated micro-particle image velocimetry (μPIV) system was used to achieve the flow structure in a serpentine micro-channel with hydraulic diameter of 0.173mm. The experimental results show the vortices around the outer and inner walls of the bend do not form when Re&lt;100. Those vortices appear and continue to develop with the Re number when Re&gt; 100-300, and the shape and size of the vortices almost remain constant when Re&gt;1000. The bend loss coefficient Kb was observed to be related with the Re number when Re&lt;100, with the Re number and channel size when Re&gt;100. It almost keeps constant and changes in the range of ± 10% When Re is larger than some value in 1300-1500. And a size effect on Kb was also observed.

A Novel Parameter for the Evaluation of Static Mixers

2018 ◽  
Author(s):  
Morgan Thomas ◽  
Thomas Eldredge ◽  
Hector Medina ◽  
David Fazzina
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Operating Time ◽  
Entropy Change ◽  
Time Cost ◽  
Transfer Rates ◽  
Static Mixers ◽  
Mixing Parameter ◽  
Potential Applications ◽  
Computational Fluid Dynamics Cfd

Static, or motionless, mixers are widely used in applications that involve chemical reactions, heat transfer, blending of fluids, or a combination of these. Within those applications, mixing can affect various parameters such as heat or mass transfer rates, process operating time, cost, safety, and product quality. Therefore, it is crucial to assess the performance of static mixers. In general, their performance is evaluated based on their ability to carry out mixing while minimizing energy loss. To accomplish this, a novel mixing parameter, the M number, is proposed and evaluated. The M number is a unitless parameter that describes the effects of the mixer using entropy change and pressure drop. The parameter is compared to another method of mixing evaluation that relies on Covariance (CoV) change across the mixer. Computational Fluid Dynamics (CFD) is executed using both methods to evaluate two static mixers and compare the results of each method. Potential applications for the M number are discussed and its limitations are noted.

Measurement of Flow Rate of Droplets and Liquid Film in Venturi Scrubber

2016 ◽  
Author(s):  
Yasuhiro Nakao ◽  
Naoki Horiguchi ◽  
Hiroyuki Yoshida ◽  
Tetsuya Kanagawa ◽  
Akiko Kaneko ◽  
...  
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Gas Phase ◽  
Flow Rate ◽  
Interfacial Area ◽  
Decontamination Factor ◽  
Liquid Film Thickness ◽  
Phase Flow ◽  
Radioactive Materials ◽  
Venturi Scrubber

As one of filtered venting systems which should be installed in light water reactors from viewpoint of protecting a containment vessel and suppressing the diffusion of radioactive materials, there is a system composed of venturi scrubbers. The radioactive materials in the contaminated gas are collected into liquid. By dispersed flow formed in the venturi scrubber, large interfacial area between liquid and gas was obtained, and large decontamination factor is realized. In evaluation for the decontamination performance of the venturi scrubber, interface of droplets and liquid film are important. However, there is a little knowledge about the interfacial area in the venturi scrubber for filtered venting. In this study, to obtain the interfacial area data, amount of the droplets and the liquid film in the venturi scrubber is evaluated by visualizing observation and sampling the liquid film at the outlet of the venturi scrubber. In the venturi scrubber, a pressure drop occurs in the throat part by the inflow of air from the compressor. Water flows from the tank by a pressure difference between a suctioned hole with head pressure and a throat part. An annular spray flow is then formed in the venturi scrubber. Therefore, the liquid flow rate changes according to the gas phase flow rate. To discharge separately the droplets and the liquid film, a rectangular separator is installed at the venturi scrubber outlet. The superficial gas phase flow rate is 25.2–292.3 m/s in the throat. As a result, the liquid film and the droplets through the wall were confirmed to be discharged separately by the separator. The ratio of the liquid film to the total amount of liquid is 80 to 95% and that of the droplets was estimated as 5 to 20%. However, the change of the liquid film thickness caused by the increase of gas phase flow rates was observed. When the liquid film thickness is large, it is possible that some liquid film flowing into the droplet side.

scholarly journals A Review of Planar PIV Systems and Image Processing Tools for Lab-On-Chip Microfluidics

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 3090 ◽  
Author(s):  
Fahrettin Ergin ◽  
Bo Watz ◽  
Nicolai Gade-Nielsen
Keyword(s):  
Image Processing ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Relevant Information ◽  
Droplet Formation ◽  
Field Investigation ◽  
Cell Counting ◽  
Lab On Chip ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry

Image-based sensor systems are quite popular in micro-scale flow investigations due to their flexibility and scalability. The aim of this manuscript is to provide an overview of current technical possibilities for Particle Image Velocimetry (PIV) systems and related image processing tools used in microfluidics applications. In general, the PIV systems and related image processing tools can be used in a myriad of applications, including (but not limited to): Mixing of chemicals, droplet formation, drug delivery, cell counting, cell sorting, cell locomotion, object detection, and object tracking. The intention is to provide some application examples to demonstrate the use of image processing solutions to overcome certain challenges encountered in microfluidics. These solutions are often in the form of image pre- and post-processing techniques, and how to use these will be described briefly in order to extract the relevant information from the raw images. In particular, three main application areas are covered: Micro mixing, droplet formation, and flow around microscopic objects. For each application, a flow field investigation is performed using Micro-Particle Image Velocimetry (µPIV). Both two-component (2C) and three-component (3C) µPIV systems are used to generate the reported results, and a brief description of these systems are included. The results include detailed velocity, concentration and interface measurements for micromixers, phase-separated velocity measurements for the micro-droplet generator, and time-resolved (TR) position, velocity and flow fields around swimming objects. Recommendations on, which technique is more suitable in a given situation are also provided.

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