Numerical Modeling of Electroosmotically Driven Micro Flows

1999 ◽  
Author(s):  
Prashanta Dutta ◽  
Ali Beskok ◽  
Timothy C. Warburton
Keyword(s):  
Spectral Element ◽  
Double Layers ◽  
Channel Height ◽  
Shear Stresses ◽  
Pressure Gradients ◽  
Pressure Distributions ◽  
Micro Channels ◽  
Micro Flows ◽  
Analytical Relations ◽  
P Type

Abstract Electroosmotically driven flows in micro-channels are analyzed analytically and numerically. Semi-analytical relations for the velocity and pressure distributions in micro channels are obtained for electric double layers that are much smaller than the channel height, by using the Helmholtz Smoluchowski velocity. Analytical relations for wall shear stress and pressure distribution are obtained. Amplification of the normal and shear stresses on the walls are observed and documented. A high-order (h/p type) spectral element method is developed, and verified for numerical simulation of electroosmotic micro fluidic flows. Finally, flow through a step channel geometry is analyzed to document the interaction of the electroosmotic forces with adverse pressure gradients. Significant changes within the separation patterns are observed.

Electroosmotic Flow Control in Complex Microgeometries

2000 ◽  
Author(s):  
Prashanta Dutta ◽  
Ali Beskok
Keyword(s):  
Flow Control ◽  
Electroosmotic Flow ◽  
Spectral Element Method ◽  
Spectral Element ◽  
Separation Control ◽  
Control Techniques ◽  
Pressure Distributions ◽  
Flow Adjustment ◽  
Analytical Relations ◽  
P Type

Abstract A high-order (h/p type) spectral element method is developed, and verified for numerical simulation of combined electroosmotic and pressure driven flows in complex microgeometries. Analytical relations for wall shear stress, velocity and pressure distributions in straight channels are obtained. The electrokinetic pumping action is demonstrated. Electroosmotic flows in groove-channels, microchannel junctions and Y-split junctions are analyzed. Precise flow adjustment and separation control techniques using the electroosmotic forces are demonstrated. In the Stokes flow regime, the flow control is shown to have linear dependence on the magnitude of the external electric field. Hence, the electroosmotic forces can be used as linear actuators for various microfluidic applications.

Experimental Studies of Adiabatic Flow Boiling in Fractal-Like Branching Micro-Channels

2008 ◽  
Author(s):  
Brian J. Daniels ◽  
James A. Liburdy ◽  
Deborah V. Pence
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Channel Length ◽  
Channel Height ◽  
Channel Network ◽  
Adiabatic Flow ◽  
Numerical Predictions ◽  
Micro Channels

Experimental results of adiabatic boiling of water flowing through a fractal-like branching microchannel network are presented and compared to numerical simulations for identical flow conditions. The fractal-like branching channel network had channel length and width ratios between adjacent branching levels of 0.7071, a total flow length of 18 mm, a channel height of 150 μm and a terminal channel width of 100 μm. The channels were DRIE etched into a silicon disk and pyrex was anodically bonded to the silicon to form the channel top and allowed visualization of the flow within the channels. The water flowed from the center of the disk where the inlet was laser cut through the silicon to the periphery of the disc. The flow rates ranged from 100 to 225 g/min and the inlet subcooling levels varied from 0.5 to 6 °C. Pressure drop across the channel as well as void fraction in each branching level were measured for each of the test conditions. The measured pressure drop ranged from 20 to 90 kPa, and the measured void fraction ranged from 0.3 to 0.9. The pressure drop results agree well with the numerical predictions. The measured void fraction results followed the same trends as the numerical results.

scholarly journals Demulsification of Kerosene/Water Emulsion in the Transparent Asymmetric Plate-Type Micro-Channel

Micromachines ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 680 ◽  
Author(s):  
Da Ruan ◽  
Diliyaer Hamiti ◽  
Zheng-Dong Ma ◽  
Ya-Dong Pu ◽  
Xiao Chen
Keyword(s):  
Optical Microscope ◽  
Channel Height ◽  
Micro Channel ◽  
Oil Droplets ◽  
Water Emulsion ◽  
Micro Channels ◽  
Demulsification Process ◽  
Surface Modified ◽  
Plate Type ◽  
Demulsification Efficiency

Asymmetric plate-type micro-channels (APM) have one hydrophobic wall and one hydrophilic wall. By flowing through APM, a kerosene-in-water emulsion can be de-emulsified in one second. To date, however, the demulsification process in the APM is still a black box. In order to observe the demulsification process directly, transparent asymmetric plate-type micro-channels (TAPM) were fabricated with two surface-modified glass plates. Emulsions with oil contents of 10%, 30%, and 50% were pumped through TAPM with heights of 39.2 μm and 159.5 μm. The movement and coalescence of oil droplets (the dispersed phase of a kerosene-in-water emulsion) in the TAPM were observed directly with an optical microscope. By analyzing videos and photographs, it was found that the demulsification process included three steps: oil droplets flowed against and were adsorbed on the hydrophobic wall, then oil droplets coalesced to form larger droplets, whereupon the oil phase was separated. The experimental results showed that the demulsification efficiency was approximately proportional to the oil content (30–50%) of the emulsions and increased when the micro-channel height was reduced.

scholarly journals Self-similar compressible turbulent boundary layers with pressure gradients. Part 1. Direct numerical simulation and assessment of Morkovin’s hypothesis

2019 ◽  
Vol 880 ◽  
pp. 239-283 ◽  
Author(s):  
Christoph Wenzel ◽  
Tobias Gibis ◽  
Markus Kloker ◽  
Ulrich Rist
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Mach Number ◽  
Direct Numerical Simulation ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Shear Stresses ◽  
Pressure Gradients ◽  
Mean Flow ◽  
Self Similar

A direct numerical simulation study of self-similar compressible flat-plate turbulent boundary layers (TBLs) with pressure gradients (PGs) has been performed for inflow Mach numbers of 0.5 and 2.0. All cases are computed with smooth PGs for both favourable and adverse PG distributions (FPG, APG) and thus are akin to experiments using a reflected-wave set-up. The equilibrium character allows for a systematic comparison between sub- and supersonic cases, enabling the isolation of pure PG effects from Mach-number effects and thus an investigation of the validity of common compressibility transformations for compressible PG TBLs. It turned out that the kinematic Rotta–Clauser parameter $\unicode[STIX]{x1D6FD}_{K}$ calculated using the incompressible form of the boundary-layer displacement thickness as length scale is the appropriate similarity parameter to compare both sub- and supersonic cases. Whereas the subsonic APG cases show trends known from incompressible flow, the interpretation of the supersonic PG cases is intricate. Both sub- and supersonic regions exist in the boundary layer, which counteract in their spatial evolution. The boundary-layer thickness $\unicode[STIX]{x1D6FF}_{99}$ and the skin-friction coefficient $c_{f}$, for instance, are therefore in a comparable range for all compressible APG cases. The evaluation of local non-dimensionalized total and turbulent shear stresses shows an almost identical behaviour for both sub- and supersonic cases characterized by similar $\unicode[STIX]{x1D6FD}_{K}$, which indicates the (approximate) validity of Morkovin’s scaling/hypothesis also for compressible PG TBLs. Likewise, the local non-dimensionalized distributions of the mean-flow pressure and the pressure fluctuations are virtually invariant to the local Mach number for same $\unicode[STIX]{x1D6FD}_{K}$-cases. In the inner layer, the van Driest transformation collapses compressible mean-flow data of the streamwise velocity component well into their nearly incompressible counterparts with the same $\unicode[STIX]{x1D6FD}_{K}$. However, noticeable differences can be observed in the wake region of the velocity profiles, depending on the strength of the PG. For both sub- and supersonic cases the recovery factor was found to be significantly decreased by APGs and increased by FPGs, but also to remain virtually constant in regions of approximated equilibrium.

Heat Transfer Characteristics of Gaseous Flows in Micro-Channels With Negative Heat Flux

2006 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Constant Heat Flux ◽  
Channel Height ◽  
Gas Temperature ◽  
Heat Transfer Characteristics ◽  
Constant Heat ◽  
Transfer Characteristics ◽  
Micro Channels ◽  
Gaseous Flows

Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in micro-channels with CHF (constant heat flux) whose value is negative. The combined effect of viscous dissipation and compressibility is also investigated. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The computations are performed for channels with constant heat flux with range from −104 to −102 Wm−2. The channel height ranges from 10 to 100 μm and the aspect ratio of the channel height and length is 200. The stagnation pressure varies from 120 to 500 kPa. The outlet pressure is fixed at the atmosphere. The wall and bulk temperatures in micro-channels are compared with those of the case of positive heat flux and also compared with those of the incompressible flow in a conventional sized channel. In the case of negative heat flux, temperature profiles normalized by heat flux have different trends in the case of positive heat flux, when flow is fast. A gas temperature falls down due to the energy conversion. A correlation for the prediction of the wall temperature of the gaseous flow in the micro-channel is proposed.

Development and Application of an Alternating-Color Micro-PIV System

2014 ◽  
Author(s):  
Shenq-Yuh Jaw ◽  
Jyh-Jong Sheen ◽  
Robert Hwang
Keyword(s):  
Color Image ◽  
Incident Light ◽  
Ccd Camera ◽  
Hydrodynamic Focusing ◽  
Micro Piv ◽  
Unique Color ◽  
Micro Channels ◽  
Micro Flows ◽  
Micro Flow ◽  
Sequential Images

In this study, light emitted from red, green, and blue LEDs is adopted as the light source of an alternating-color micro-PIV system for micro flows measurement. The strobe frequency of the LED can easily reach 20,000Hz, which is high enough to provide the time resolution required for most micro flows measurement. A cardioid annular condenser is adopted in the micro-PIV system so that the incident light from the LED is redirected and only the light emitted from fluorescent particles reaches the object lens of the microscope. The image quality is significantly improved. Clear dark background particle images of micro flows are recorded from the proposed LED micro-PIV system. In addition, the diffraction limit of the microscope is improved from half of the wavelength to one-fifth of the wavelength. For alternating-color multiple-exposure image application, a triple-exposure alternating-color image — sequentially illuminated by red, green, and blue LED light — is recorded on a single frame by a color CCD camera. Three unique color images — a blue, a green, and a red image respectively — are obtained from separating the triple-exposure image. With three sequential images available, the velocity, acceleration distributions of micro flow, and different phases of the multiphase flow can be measured from these unique color sequential images. The alternating-color micro-PIV system is then applied to measure micro flow past a cylinder, circulation in a micro-droplet, hydrodynamic focusing sheath flow, and two-phase flow in micro channels. Satisfactory results are obtained for all the flows measured.

Analytical Solution for Thermally Fully Developed Combined Electroosmotic and Pressure-Driven Flows in Narrow Confinements With Thick Electrical Double Layers

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Ranabir Dey ◽  
Debapriya Chakraborty ◽  
Suman Chakraborty
Keyword(s):  
Viscous Dissipation ◽  
Joule Heating ◽  
Double Layers ◽  
Channel Height ◽  
Flux Boundary Condition ◽  
Closed Form Solutions ◽  
Electrical Double Layers ◽  
Constant Wall Heat Flux ◽  
Standard Models ◽  
Pressure Driven

In the present paper, closed form solutions for the Nusselt number are obtained for hydrodynamically and thermally fully developed combined electroosmotic and pressure-driven flows in narrow confinements for the constant wall heat flux boundary condition. Overcoming the constraints of the standard models that are valid only within thin electrical double layer (EDL) limits, the effects of thick electric double layers are accounted for as a distinctive feature of this model. Along with Joule heating, viscous dissipation effects, which are particularly important for ultrathin channel dimensions (typically conforming to the cases of thick EDLs), are taken into account. The results are presented in terms of appropriate nondimensional parameters depicting the relative EDL thickness with respect to the channel height, as well as relative strengths of Joule heating and viscous dissipation effects.

scholarly journals Analysis of an electroosmotic flow in wavy wall microchannels using the lubrication approximation

2020 ◽  
Vol 66 (6 Nov-Dec) ◽  
pp. 761
Author(s):  
J. Arcos ◽  
O. Bautista ◽  
F. Méndez ◽  
M. Peralta
Keyword(s):  
Electroosmotic Flow ◽  
Mathematical Problem ◽  
Volumetric Flow Rate ◽  
Double Layers ◽  
Channel Height ◽  
Wavy Wall ◽  
Poisson Boltzmann ◽  
Hydrodynamic Field ◽  
The Mean ◽  
Analytical Expressions

We present the analysis of an electroosmotic flow (EOF) of a Newtonian fluid in a wavy-wall microchannel. In order to describe the flow and electrical fields, the lubrication and Debye-Hückel approximations are used. The simplified governing equations of continuity, momentum and Poisson-Boltzmann, together with the boundary conditions are presented in dimensionless form. For solving the mathematical problem, numerical and asymptotic techniques were applied. The asymptotic solution is obtained in the limit of very thin electric double layers (EDLs). We show that the lubrication theory is a powerful technique for solving the hydrodynamic field in electroosmotic flows in microchannels where the amplitude of the waviness changes on the order of the  mean semi-channel height. Approximate analytical expressions for the velocity components and pressure distribution are derived, and a closed formula for the volumetric flow rate is obtained.  The results show that the principal parameters that govern this EOF are the geometrical parameter, ε, which characterizes the waviness of the microchannel and the ratio of the mean semi-channel height to the thickness of the EDL, κ.

Visualisation of Turbulent Wedges Under Favourable Pressure Gradients Using Both Shear-Sensitive and Temperature-Sensitive Liquid Crystals

2002 ◽  
Author(s):  
S. Zhong ◽  
T. P. Chong ◽  
H. P. Hodson
Keyword(s):  
Liquid Crystals ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Turbine Blades ◽  
Temperature Sensitive ◽  
Shear Stresses ◽  
Pressure Gradients ◽  
Surface Shear ◽  
The Difference ◽  
Thermal Boundary Layers

Turbulent wedges induced by a 3D surface roughness placed in a laminar boundary layer over a flat plate were visualised for the first time using both shear-sensitive and temperature-sensitive liquid crystals. The experiments were carried out at three different levels of favourable pressure gradients. The purpose of this investigation was to examine the spreading angles of the turbulent wedges indicated by their associated surface shear stresses and heat transfer characteristics and hence obtain further insight about the difference in the behaviour of transitional momentum and thermal boundary layers when a streamwise pressure gradient exists. It was shown that under a zero pressure gradient the spreading angles indicated by the two types of liquid crystals are the same, but the difference increases as the level of favourable pressure gradient increases. The result from the present study could have an important implication to the transition modelling of thermal boundary layers over gas turbine blades.

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