scholarly journals Motion of an Elastic Capsule in a Trapezoidal Microchannel under Stokes Flow Conditions

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1144
Author(s):  
Abdollah Koolivand ◽  
Panagiotis Dimitrakopoulos
Keyword(s):  
Steady State ◽  
Cross Sections ◽  
Single Phase ◽  
Channel Length ◽  
Flow Conditions ◽  
Membrane Rupture ◽  
Trapezoidal Microchannel ◽  
Capsule Dynamics ◽  
Spherical Capsule ◽  
Surrounding Fluid

Even though the research interest in the last decades has been mainly focused on the capsule dynamics in cylindrical or rectangular ducts, channels with asymmetric cross-sections may also be desirable especially for capsule migration and sorting. Therefore, in the present study we investigate computationally the motion of an elastic spherical capsule in an isosceles trapezoidal microchannel at low and moderate flow rates under the Stokes regime. The steady-state capsule location is quite close to the location where the single-phase velocity of the surrounding fluid is maximized. Owing to the asymmetry of the trapezoidal channel, the capsule’s steady-state shape is asymmetric while its membrane slowly tank-treads. In addition, our investigation reveals that tall trapezoidal channels with low base ratios produce significant off-center migration for large capsules compared to that for smaller capsules for a given channel length. Thus, we propose a microdevice for the sorting of artificial and physiological capsules based on their size, by utilizing tall trapezoidal microchannels with low base ratios. The proposed sorting microdevice can be readily produced via glass fabrication or as a microfluidic device via micromilling, while the required flow conditions do not cause membrane rupture.

Liquid Mixing in Static Micro Mixers With Various Cross Sections

2003 ◽  
Author(s):  
Norbert Kockmann ◽  
Michael Engler ◽  
Claus Fo¨ll ◽  
Peter Woias
Keyword(s):  
Mass Transfer ◽  
Laminar Flow ◽  
Cross Sections ◽  
A Priori ◽  
Channel Length ◽  
Convective Transport ◽  
Geometrical Parameters ◽  
Flow Conditions ◽  
Wide Range ◽  
Mixing Quality

Micro mixers are an integral part of several micro fluidic devices like micro reactors or analytical equipment. Due to the small dimensions, laminar flow is expected a priori in those devices while the mass transfer is supposed to be dominated by diffusion. A detailed numerical CFD-study by CFDRC-ACE+ of simple static mixers shows a significant deviation from strictly laminar flow in a wide range of Reynolds numbers Re, channel dimensions, and types of cross sections (square, rectangular, trapezoidal). With increasing flow velocity and Re number the flow starts to form vortexes at the entrance of the mixing channel. The vortexes are symmetrical to the symmetry planes of the mixing channel, both for the rectangular and the trapezoidal cross sections investigated here. With further increasing velocity the flow tends to instabilities, which causes a breakup of the flow symmetry. These instabilities are generally found in T-shape mixers with symmetrical flow conditions, but not always in Y-shape mixers or with asymmetrical flow conditions. Within the laminar flow regime diffusive mass transfer is dominant. In this case the mixing quality at constant channel length becomes worse with increasing velocity. This effect can almost be equalized by the onset of the vortex regime, which enhances the mass transfer by convective transport. This paper shows the mixing quality at a certain length for different geometrical parameters and flow conditions.

scholarly journals A dynamic rating curve approach to indirect discharge measurement

2009 ◽  
Vol 13 (6) ◽  
pp. 847-863 ◽  
Author(s):  
F. Dottori ◽  
M. L. V. Martina ◽  
E. Todini
Keyword(s):  
Steady State ◽  
Unsteady Flow ◽  
Cross Sections ◽  
Accurate Estimation ◽  
Rating Curve ◽  
Flow Conditions ◽  
Estimation Errors ◽  
Flow Equations ◽  
Wide Range ◽  
Rating Curves

Abstract. The operational measurement of discharge in medium and large rivers is mostly based on indirect approaches by converting water stages into discharge on the basis of steady-flow rating curves. Unfortunately, under unsteady flow conditions, this approach does not guarantee accurate estimation of the discharge due, on the one hand, to the underlying steady state assumptions and, on the other hand, to the required extrapolation of the rating curve beyond the range of actual measurements used for its derivation. Historically, several formulae were proposed to correct the steady-state discharge value and to approximate the unsteady-flow stage-discharge relationship. In the majority of these methods, the correction is made on the basis of water level measurements taken at a single cross section where a steady state rating curve is available, while other methods explicitly account for the water surface slope using stage measurements in two reference sections. However, most of the formulae available in literature are either over-simplified or based on approximations that prevent their generalisation. Moreover they have been rarely tested on cases where their use becomes essential, namely under unsteady-flow conditions characterised by wide loop rating curves. In the present work, an original approach, based on simultaneous stage measurements at two adjacent cross sections, is introduced and compared to the approaches described in the literature. The most relevant feature is that the proposed procedure allows for the application of the full dynamic flow equations without restrictive hypotheses. The comparison has been carried out on channels with constant or spatially variable geometry under a wide range of flood wave and river bed slope conditions. The results clearly show the improvement in the discharge estimation and the reduction of estimation errors obtainable using the proposed approach.

Critical Review of Stabilized Nanoparticle Transport in Porous Media

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Xiaoyan Meng ◽  
Daoyong Yang
Keyword(s):  
Porous Media ◽  
Steady State ◽  
Single Phase ◽  
Transient Flow ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Flow Conditions ◽  
Nanoparticle Transport ◽  
Two Phase ◽  
Transport In Porous Media

Over the past few decades, due to the special features (i.e., easily produced, large-surface-area-to-volume ratio, and engineered particles with designed surface properties), nanoparticles have not only attracted great attentions from the oil and gas industry but also had various applications from drilling and completion, reservoir characterization, to enhanced oil recovery (EOR). As sensors or EOR agents, thus, fate and behavior of nanoparticles in porous media are essential and need to be investigated thoroughly. Nevertheless, most of the published review papers focus on particle transport in saturated porous media, and all of them are about steady-state flow conditions. So far, no attempts have been extended to systematically review current knowledge about nanoparticle transport in porous media with single-phase and two-phase flow systems under both steady-state and unsteady-state conditions. Accordingly, this review will discuss nanoparticle transport phenomena in porous media with its focus on the filtration mechanisms, the underlying interaction forces, and factors dominating nanoparticle transport behavior in porous media. Finally, mathematical models used to describe nanoparticle transport in porous media for both single-phase flow and two-phase flow under steady-state and transient flow conditions will be summarized, respectively.

scholarly journals A dynamic rating curve approach to indirect discharge measurement

2009 ◽  
Vol 6 (1) ◽  
pp. 859-896 ◽  
Author(s):  
F. Dottori ◽  
M. L. V. Martina ◽  
E. Todini
Keyword(s):  
Steady State ◽  
Unsteady Flow ◽  
Cross Sections ◽  
Accurate Estimation ◽  
Rating Curve ◽  
Flow Conditions ◽  
Estimation Errors ◽  
River Bed ◽  
Wide Range ◽  
Rating Curves

Abstract. The operational measurement of discharge in medium and large rivers is mostly based on indirect approaches by converting water stages into discharge on the basis of steady-flow rating curves. Unfortunately, under unsteady flow conditions, this approach does not guarantee accurate estimation of the discharge due, on the one hand, to the underlying steady state assumptions and, on the other hand, to the required extrapolation of the rating curve beyond the range of actual measurements used for its derivation. Historically, several formulas were proposed to correct the steady-state discharge value and to approximate the unsteady-flow stage-discharge relationship on the basis of water level measurements taken at a single cross section, where a steady state rating curve is available. However, most of them are either over-simplified or based on approximations that prevented their generalisation. Moreover all the mentioned formulas have been rarely tested on cases where their use becomes essential, namely under unsteady-flow conditions characterised by wide loop rating curves. In the present work, a new approach, based on simultaneous stage measurements at two adjacent cross sections, is introduced and compared to the approaches described in the literature. The comparison has been carried out on channels with constant or spatially variable geometry under a wide range of flood wave and river bed slope conditions. The results clearly show the improvement in the discharge estimation and the reduction of estimation errors obtainable using the proposed approach.

Validation of SAS4A/SASSYS-1 for predicting steady-state single-phase natural circulation

2021 ◽  
Vol 377 ◽  
pp. 111149
Author(s):  
Taiyang Zhang ◽  
Erik R. Smith ◽  
Caleb S. Brooks ◽  
Thomas H. Fanning
Keyword(s):  
Steady State ◽  
Single Phase ◽  
Natural Circulation

Improved Load Sharing Control Techniques for Inverters used in a Microgrid

2009 ◽  
Vol 10 (1) ◽  
Author(s):  
Wei Yao ◽  
Zhaoming Qian
Keyword(s):  
Steady State ◽  
Transient Response ◽  
Single Phase ◽  
Load Sharing ◽  
Power Sharing ◽  
Experimental Results ◽  
Control Technique ◽  
Transient Performance ◽  
Control Techniques ◽  
Control Scheme

In this paper, an improved load sharing control scheme is presented, which is able to improve the transient response and power sharing accuracy of parallel-connected inverters used in microgrid. It also shows how the improved droop method can be easily adapted to account for the operation of parallel-connected inverters, providing good performance under the variation and disturbance of loads, as well as achieving good steady-state objectives and transient performance. Two DSP-based single-phase Microgrid inverters are designed and implemented. Simulation and experimental results are all reported, confirming the validity of the proposed control technique.

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