Evaluation of the Mixing Performance of the Micromixers With Grooved or Obstructed Channels

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Yeng-Yung Tsui ◽  
Ching-Shiang Yang ◽  
Chung-Ming Hsieh
Keyword(s):  
Vertical Plane ◽  
Pressure Head ◽  
Fluid Mixing ◽  
Mixing Performance ◽  
Large Pressure ◽  
Fluid Concentration ◽  
Speed Up ◽  
Periodic Configuration ◽  
The Cost ◽  
Good Agreement

The mixing flows in microchannels were examined using numerical methods. To speed up fluid mixing, it is essential to generate lateral transport of mass. In this study, the mixing flow is disrupted by either placing grooves or block obstacles on the walls of the channels. Since the grooves or the blocks appear in a periodic configuration, the velocity is solved only in a section of the channel. With the repeating cycle of flow velocity field, the fluid concentration can be calculated throughout the entire length of the channel. Good agreement with experiments in the mixing performance justifies the present methodology. Two different channel configurations are under consideration: grooved channels and obstructed channels. The results reveal that with straight grooves, a well organized vortex flow is formed in the vertical plane along the groove, which leads to a helical flow in the channel. The mixing performance can be enhanced by having grooves on both the top and the bottom walls arranged in a staggered manner, by which the transversal velocity is largely increased. It is seen that the strength of the secondary flow and, thus, the mixing can be improved by suitably choosing geometric parameters of the groove, such as the depth, the width, and the oblique angle. It is also shown that the efficient mixing for the staggered herringbone type groove is due to the fluid stratification caused by the exchange of position of the resulted counter-rotating vortices. As for the obstructed channels, the flows are in essence two dimensional. Very strong transversal velocity can be produced by narrowing down the flow passage in the channel. However, the efficient mixing is obtained at the cost of large pressure head loss.

Numerical Modeling and Experimental Investigation of Improved Mixing From Both Coriolis Effect and Go¨rtler Vortices in Rotating Zigzag Microchannel

2011 ◽  
Author(s):  
Yong Ren ◽  
Wallace Woon-Fong Leung
Keyword(s):  
Pressure Head ◽  
Stationary Condition ◽  
Coriolis Effect ◽  
Straight Channel ◽  
Centrifugal Effect ◽  
Cross Sectional ◽  
Mixing Performance ◽  
Study Results ◽  
The Cost ◽  
Zigzag Shape

The flow pattern and mixing performance in different geometries of microchannels are investigated. A study for the zigzag shape channel under both stationary and rotation condition was investigated. The results are compared to the straight channel. Both numerical model via CFD and experiments are agreeing with each other. It is found when the channel is under rotation, the mixing performance is better than the stationary condition due to rotation induced Coriolis effect. As the rotation speed increases from 300rpm to 900rpm, an improved mixing performance can be further obtained. Our study results also demonstrate that zigzag channel can provide relatively better mixing, because the successive bending design can lead to secondary flow in the cross sectional directions due to Go¨rtler vortices generated from centrifugal effect as the flow negotiates the “turns” or “bends” of the channel, and this adds to mixing in addition to that due to aforementioned Coriolis effect. An analysis reveals that zigzag shape channel requires more pressure drop when compared with the straight channel in order to maintain the continuous throughflow due to the pressure/head loss as the flow encounters each bend and these losses become additive. This adds to the cost for the improved mixing from the Go¨rtler vortices.

scholarly journals Enhancement of Fluid Mixing with U-Shaped Channels on a Rotating Disc

Micromachines ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1110
Author(s):  
Chi-Wei Hsu ◽  
Po-Tin Shih ◽  
Jerry M. Chen
Keyword(s):  
Secondary Flow ◽  
Rotational Speed ◽  
Fluid Mixing ◽  
Maximum Efficiency ◽  
Mixing Efficiency ◽  
Rotating Disc ◽  
Mixing Performance ◽  
Simple Geometry ◽  
Visualization Experiments ◽  
Good Agreement

In this study, centrifugal microfluidics with a simple geometry of U-shaped structure was designed, fabricated and analyzed to attain rapid and efficient fluid mixing. Visualization experiments together with numerical simulations were carried out to investigate the mixing behavior for the microfluidics with single, double and triple U-shaped structures, where each of the U-structures consisted of four consecutive 90° bends. It is found that the U-shaped structure markedly enhances mixing by transverse secondary flow that is originated from the Coriolis-induced vortices and further intensified by the Dean force generated as the stream turns along the 90° bends. The secondary flow becomes stronger with increasing rotational speed and with more U-shaped structures, hence higher mixing performance. The mixing efficiency measured for the three types of mixers shows a sharp increase with increasing rotational speed in the lower range. As the rotational speed further increases, nearly complete mixing can be achieved at 600 rpm for the triple-U mixer and at 720 rpm for the double-U mixer, while a maximum efficiency level of 83–86% is reached for the single-U mixer. The simulation results that reveal detailed characteristics of the flow and concentration fields are in good agreement with the experiments.

scholarly journals Simulation of Thermal and Electric Field Distribution in Packaged Sausages Heated in a Stationary Versus a Rotating Microwave Oven

Foods ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1622
Author(s):  
Wipawee Tepnatim ◽  
Witchuda Daud ◽  
Pitiya Kamonpatana
Keyword(s):  
Temperature Distribution ◽  
Electric Field ◽  
Three Dimensional ◽  
Development Stage ◽  
Microwave Oven ◽  
Computational Time ◽  
Plastic Package ◽  
Heating Uniformity ◽  
The Cost ◽  
Good Agreement

The microwave oven has become a standard appliance to reheat or cook meals in households and convenience stores. However, the main problem of microwave heating is the non-uniform temperature distribution, which may affect food quality and health safety. A three-dimensional mathematical model was developed to simulate the temperature distribution of four ready-to-eat sausages in a plastic package in a stationary versus a rotating microwave oven, and the model was validated experimentally. COMSOL software was applied to predict sausage temperatures at different orientations for the stationary microwave model, whereas COMSOL and COMSOL in combination with MATLAB software were used for a rotating microwave model. A sausage orientation at 135° with the waveguide was similar to that using the rotating microwave model regarding uniform thermal and electric field distributions. Both rotating models provided good agreement between the predicted and actual values and had greater precision than the stationary model. In addition, the computational time using COMSOL in combination with MATLAB was reduced by 60% compared to COMSOL alone. Consequently, the models could assist food producers and associations in designing packaging materials to prevent leakage of the packaging compound, developing new products and applications to improve product heating uniformity, and reducing the cost and time of the research and development stage.

Efficient Fatigue Testing of Tubular Joints

2015 ◽  
Author(s):  
P. Thibaux ◽  
J. Van Wittenberghe ◽  
E. Van Pottelberg ◽  
M. Van Poucke ◽  
P. De Baets ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Testing ◽  
Fatigue Loading ◽  
Tubular Joints ◽  
Testing Method ◽  
Out Of Plane ◽  
Resonance Principle ◽  
Tubular Joint ◽  
The Cost ◽  
Good Agreement

Tubular joints are intensively used in off-shore structures for shallow waters. Depending on the sea conditions and the type of structure, the design can be fatigue driven. This is particularly the case for off-shore wind turbines, where turbulences are generating a fatigue loading. Any improvement of the fatigue performance of the tubular joint would be beneficial to reduce the weight and the cost of the structure. To assess efficiently the fatigue resistance of the tubular joint, a testing method has been developed based on the resonance principle. The complete circumference of the welded joint can be loaded, successively in the in-plane and out-of-plane modes at a frequency close to 20Hz. Finite element computations were used to investigate the feasibility of the concept. Then, an X-node was made and successfully tested to investigate the stress distribution along the weld. The experimental results were compared with finite element computations, giving a good agreement.

Sparse Incremental Delta-Bar-Delta for System Identification

2014 ◽  
Vol 665 ◽  
pp. 643-646
Author(s):  
Ying Liu ◽  
Yan Ye ◽  
Chun Guang Li
Keyword(s):  
System Identification ◽  
Cost Function ◽  
Learning Algorithm ◽  
Learning System ◽  
The Other ◽  
Sparse System ◽  
Speed Up ◽  
Sparse System Identification ◽  
The Cost ◽  
Zero Attractor

Metalearning algorithm learns the base learning algorithm, targeted for improving the performance of the learning system. The incremental delta-bar-delta (IDBD) algorithm is such a metalearning algorithm. On the other hand, sparse algorithms are gaining popularity due to their good performance and wide applications. In this paper, we propose a sparse IDBD algorithm by taking the sparsity of the systems into account. Thenorm penalty is contained in the cost function of the standard IDBD, which is equivalent to adding a zero attractor in the iterations, thus can speed up convergence if the system of interest is indeed sparse. Simulations demonstrate that the proposed algorithm is superior to the competing algorithms in sparse system identification.

Numerical analysis of non-aligned inputs M-type micromixers with different shaped obstacles for biomedical applications

2021 ◽  
pp. 095440892110516
Author(s):  
Muhammad Irfan ◽  
Imran Shah ◽  
Usama M Niazi ◽  
Muhsin Ali ◽  
Sadaqat Ali ◽  
...  
Keyword(s):  
Structural Design ◽  
Biomedical Applications ◽  
Structural Changes ◽  
Nanoparticle Synthesis ◽  
Fluid Mixing ◽  
The Novel ◽  
Flow Conditions ◽  
Mixing Index ◽  
Mixing Performance ◽  
Passive Micromixer

Fluid mixing in lab-on-a-chip devices at laminar flow conditions result in a low mixing index. The reason is dominant diffusion over the convection process. The mixing index can be improved by certain changes in the micromixer structural design like introducing obstacles in the path of fluid flow. These obstacles will make dominant the advection process over the diffusion process. The main contribution of this work is based on proposing the novel hybrid type micromixer design for enhancing the mixing quality. Three non-aligned M-type and non-aligned M-type with obstacles passive type micromixers are analyzed by COMSOL5.5. These designs are hybrid types because different structural changes are combined in a single design for mixing improvement. First of all the straight non-aligned inlets, M-type passive micromixer (SMTM) is analyzed. It is observed that mixing performance is improved because of M-shaped mixing units and non-aligned inlets. This improvement is deemed to be not enough so different shaped obstacles are introduced in the micromixer design. These designs based on obstacles are named horizontal rectangular M-type micromixer, square M-type micromixer, and vertical rectangular M-type micromixer. The mixing index for SMTM, square M-type micromixer, horizontal rectangular M-type micromixer, and vertical rectangular M-type micromixer at Reynolds number Re = 60 is respectively given by 71.1%, 83.21%, 84.45%, and 89.99%. The mixing index of vertical rectangular M-type micromixer was 59.34% − 87.65% for Re = 0.5–100. Vertical rectangular M-type micromixer is concluded with the better-mixing capability design among the proposed ones. Based on these simulation results, the vertical rectangular M-type micromixer design can be utilized for mixing purposes in biomedical applications like nanoparticle synthesis and biomedical sample preparation for drug delivery.

scholarly journals Asymmetrical Induced Charge Electroosmotic Flow on a Herringbone Floating Electrode and Its Application in a Micromixer

Micromachines ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 391 ◽  
Author(s):  
Qingming Hu ◽  
Jianhua Guo ◽  
Zhongliang Cao ◽  
Hongyuan Jiang
Keyword(s):  
Electrode Surface ◽  
Slip Velocity ◽  
Fluid Velocity ◽  
Laminar Flows ◽  
Fluid Mixing ◽  
Electrode Pair ◽  
Great Opportunity ◽  
Mixing Performance ◽  
Induced Charge ◽  
Floating Electrode

Enhancing mixing is of significant importance in microfluidic devices characterized by laminar flows and low Reynolds numbers. An asymmetrical induced charge electroosmotic (ICEO) vortex pair generated on the herringbone floating electrode can disturb the interface of two-phase fluids and deliver the fluid transversely, which could be exploited to accomplish fluid mixing between two neighbouring fluids in a microscale system. Herein we present a micromixer based on an asymmetrical ICEO flow induced above the herringbone floating electrode array surface. We investigate the average transverse ICEO slip velocity on the Ridge/Vee/herringbone floating electrode and find that the microvortex generated on the herringbone electrode surface has good potential for mixing the miscible liquids in microfluidic systems. In addition, we explore the effect of applied frequencies and bulk conductivity on the slip velocity above the herringbone floating electrode surface. The high dependence of mixing performance on the floating electrode pair numbers is analysed simultaneously. Finally, we investigate systematically voltage intensity, applied frequencies, inlet fluid velocity and liquid conductivity on the mixing performance of the proposed device. The microfluidic micromixer put forward herein offers great opportunity for fluid mixing in the field of micro total analysis systems.

Isothermal Bubble Motion Through a Rotating Liquid

1972 ◽  
Vol 94 (1) ◽  
pp. 187-192 ◽  
Author(s):  
D. L. Schrage ◽  
H. C. Perkins
Keyword(s):  
Radial Direction ◽  
Terminal Velocity ◽  
Distilled Water ◽  
Analytical Prediction ◽  
Bubble Motion ◽  
Large Pressure ◽  
Rotating Liquid ◽  
Angular Velocities ◽  
Large Pressure Gradient ◽  
Good Agreement

An analytical and experimental study of isothermal bubble motion through a liguid which is itself in motion is presented. Both analytical and experimental results are reported for the velocities and trajectories of oxygen bubbles moving through a liquid annulus which is rotating at angular velocities ranging from 500 to 1500 rpm. Results are presented for both distilled water and glycerin. The analytical prediction of the trajectories and velocities showed good agreement with the experimental data. It was found that the bubbles, which were injected at the exterior of the liquid annulus, spiralled inward rapidly and, due to the large pressure gradient in the radial direction, did not reach a constant or terminal velocity.

scholarly journals Fine-Tuning by Curriculum Learning for Non-Autoregressive Neural Machine Translation

2020 ◽  
Vol 34 (05) ◽  
pp. 7839-7846
Author(s):  
Junliang Guo ◽  
Xu Tan ◽  
Linli Xu ◽  
Tao Qin ◽  
Enhong Chen ◽  
...  
Keyword(s):  
Machine Translation ◽  
Fine Tuning ◽  
Inference Process ◽  
Neural Machine Translation ◽  
Training Strategy ◽  
Speed Up ◽  
Good Improvement ◽  
Tuning Process ◽  
Translation Accuracy ◽  
The Cost

Non-autoregressive translation (NAT) models remove the dependence on previous target tokens and generate all target tokens in parallel, resulting in significant inference speedup but at the cost of inferior translation accuracy compared to autoregressive translation (AT) models. Considering that AT models have higher accuracy and are easier to train than NAT models, and both of them share the same model configurations, a natural idea to improve the accuracy of NAT models is to transfer a well-trained AT model to an NAT model through fine-tuning. However, since AT and NAT models differ greatly in training strategy, straightforward fine-tuning does not work well. In this work, we introduce curriculum learning into fine-tuning for NAT. Specifically, we design a curriculum in the fine-tuning process to progressively switch the training from autoregressive generation to non-autoregressive generation. Experiments on four benchmark translation datasets show that the proposed method achieves good improvement (more than 1 BLEU score) over previous NAT baselines in terms of translation accuracy, and greatly speed up (more than 10 times) the inference process over AT baselines.

scholarly journals Numerical Study of T-Shaped Micromixers with Vortex-Inducing Obstacles in the Inlet Channels

Micromachines ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1122
Author(s):  
Chih-Yang Wu ◽  
Bing-Hao Lai
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Number ◽  
Particle Tracking ◽  
Concentration Distribution ◽  
Numerical Study ◽  
Fluid Mixing ◽  
Sudden Increase ◽  
New Approach ◽  
Mixing Performance ◽  
Flow Modification

To enhance fluid mixing, a new approach for inlet flow modification by adding vortex-inducing obstacles (VIOs) in the inlet channels of a T-shaped micromixer is proposed and investigated in this work. We use a commercial computational fluid dynamics code to calculate the pressure and the velocity vectors and, to reduce the numerical diffusion in high-Peclet-number flows, we employ the particle-tracking simulation with an approximation diffusion model to calculate the concentration distribution in the micromixers. The effects of geometric parameters, including the distance between the obstacles and the angle of attack of the obstacles, on the mixing performance of micromixers are studied. From the results, we can observe the following trends: (i) the stretched contact surface between different fluids caused by antisymmetric VIOs happens for the cases with the Reynolds number (Re) greater than or equal to 27 and the enhancement of mixing increases with the increase of Reynolds number gradually, and (ii) the onset of the engulfment flow happens at Re≈125 in the T-shaped mixer with symmetric VIOs or at Re≈140 in the standard planar T-shaped mixer and results in a sudden increase of the degree of mixing. The results indicate that the early initiation of transversal convection by either symmetric or antisymmetric VIOs can enhance fluid mixing at a relatively lower Re.

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