Transient Joule Heating and Its Effects on Electroosmotic Flow in a Microcapillary Packed Wth Microspheres

2005 ◽  
Author(s):  
Yuejun Kang ◽  
Chun Yang ◽  
Xiaoyang Huang
Keyword(s):  
Temperature Gradient ◽  
Electric Field ◽  
Joule Heating ◽  
Electroosmotic Flow ◽  
Flow Direction ◽  
Radial Profile ◽  
Fluid Phase ◽  
Momentum Equation ◽  
Local Electric Field ◽  
Continuity Equations

The Joule heating induced temperature development and its effects on the electroosmotic flow in a capillary packed with microspheres is analyzed in this paper using finite-difference based numerical method. The model incorporates the coupled momentum equation for the electroosmotic velocity, the energy equations for temperature distributions, and the mass and electric current continuity equations. The temperature-dependent physical properties of the electrolyte solution are taken into consideration. The simulation predicts that, in the presence of Joule heating, there exists a significant axial temperature gradient in the thermal entrance region. This high temperature gradient strongly enhances the local electric field at the entrance, resulting in a non-uniform distribution along the flow direction. The temperature shows a parabolic radial profile but the gradient is very small due to the small system Biot number. The non-uniform temperature distribution in turn greatly affects the EOF velocity by means of changing the local viscosity and the dielectric constant of the fluid phase, and the local electric field strength. The results by this model are found to be in a good agreement with published analytical and experimental works in the literature.

Towards High Concentration Enhancement of Microfluidic Temperature Gradient Focusing of Sample Solutes

2011 ◽  
Author(s):  
Zhengwei Ge ◽  
Chun Yang
Keyword(s):  
Temperature Gradient ◽  
Electric Field ◽  
Joule Heating ◽  
Electroosmotic Flow ◽  
High Concentration ◽  
Temperature Gradient Focusing ◽  
Heating Effects ◽  
Concentration Enhancement ◽  
Dc Electric Field ◽  
High Frequency Ac

This paper reports an improved technique to enhance microfluidic temperature gradient focusing (TGF) of sample solutes using Joule heating effects induced by a combined AC and DC electric field. By introducing the AC field component, additional Joule heating effects are obtained to generate temperature gradient for concentrating sample solutes, while the electroosmotic flow is suppressed under the high frequency AC electric field. Therefore, the required DC voltages for achieving certain sample concentration by Joule heating induced TGF technique are remarkably reduced. Moreover, the lower DC voltages lead to smaller electroosmotic flow (EOF), thereby reducing the backpressure effects due to the finite reservoir size. Concentration enhancements of sample solutes are improved by using a combined AC and DC electric field.

Microfluidics Concentration of Sample Solutes Using Joule Heating Effects Under Combined AC and DC Electric Field

2010 ◽  
Author(s):  
Zhengwei Ge ◽  
Chun Yang
Keyword(s):  
Temperature Gradient ◽  
Electric Field ◽  
Joule Heating ◽  
Electroosmotic Flow ◽  
Heating Effect ◽  
Dc Voltage ◽  
Joule Heating Effect ◽  
Heating Effects ◽  
Concentration Enhancement ◽  
Dc Electric Field

Microfluidic concentration is achieved by utilizing Joule heating effect induced temperature gradient focusing (TGF) under a combined AC and DC electric field imposed in a straight microchannel with sudden expansion in cross-section. The introduction of AC electric field component services dual functions: one is to produce Joule heating effects for generating temperature gradient, and the other is to suppress electroosmotic flow with high frequencies. Therefore, the required DC voltage for achieving sample concentration with Joule heating induced TGF technique is remarkably reduced. The lower DC voltage can lead to smaller electroosmotic flow (EOF), thereby reducing the backpressure effect due to the finite reservoir size. It was demonstrated that using the proposed new TGF technique with Joule heating effect under a combined AC and DC field, more than 2500-fold concentration enhancement was obtained within 14 minutes in a PDMS/PDMS microdevice, which is an order of magnitude higher than the literature reported concentration enhancement achieved by microfluidic devices utilizing the Joule heating induced TGF technique.

Joule Heating Induced Temperature Gradient Focusing for Microfluidic Concentration of Samples

2010 ◽  
Author(s):  
Zhengwei Ge ◽  
Chun Yang
Keyword(s):  
Temperature Gradient ◽  
Electric Field ◽  
Joule Heating ◽  
Field Experiments ◽  
Dc Voltage ◽  
Sample Concentration ◽  
Great Achievement ◽  
Temperature Gradient Focusing ◽  
Concentration Enhancement ◽  
High Frequency Ac

Microfluidic concentration of sample species is achieved using the temperature gradient focusing (TGF) in a microchannel with a step change in the cross-section under a pure direct current (DC) field or a combined alternating current (AC) and DC electric field. Experiments were carried out to study the effects of applied voltage, buffer concentration and channel size on sample concentration in the TGF processes. These effects were analyzed and summarized using a dimensionless Joule number that is introduced in this study. In addition, Joule number effect in the Poly-dimethylsiloxane (PDMS)/PDMS microdevice was compared with the PDMS/Glass microdevice. A more than 450-fold concentration enhancement was obtained within 75 seconds in the PDMS/PDMS microdevice. Results also showed that the high frequency AC electric field which contributes to produce the temperature gradient and reduces the required DC voltage for the sample concentration. The lower DC voltage has generated slower electroosmotic flow (EOF), which reduces the backpressure effect associated with the finite reservoir size. Finally, a more than 2500-fold concentration enhancement was obtained within 14 minutes in the PDMS/PDMS microdevice, which was a great achievement in this TGF technique using inherent Joule heating effects.

Electroosmotic Flow Field Measurements With Particle Image Velocimetry

2000 ◽  
Author(s):  
Shankar Devasenathipathy ◽  
Joshua I. Molho ◽  
James C. Mikkelsen ◽  
Juan G. Santiago ◽  
Kohsei Takehara
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Electric Field ◽  
Particle Tracking ◽  
Electroosmotic Flow ◽  
Particle Image ◽  
Field Measurements ◽  
Local Electric Field ◽  
Seed Particles ◽  
Image Velocimetry

Abstract A micron-resolution particle image velocimetry (PIV) system has been developed to spatially and temporally resolve electroosmotic flow fields within microfluidic bioanalytical devices. A second diagnostic technique, particle tracking velocimetry (PTV) has been used to determine the distribution of electrophoretic mobilities of seed particles and thereby make the PIV measurements quantitative. This second particle tracking technique has been used to determine probability distribution functions of the seed particles. Results from simulations of electric fields yield local electric field strengths in the geometries of interest. The measured mean mobility of the seed particles (obtained from PTV measurements) is then multiplied by the local electric field vector to obtain the electrophoretic velocity. The variance on the particle mobility measurement influences the errors introduced in the electroosmotic flow measurements. After total particle velocities are measured within a microfluidic system of interest, the seed particle electrophoretic velocities are subtracted from the PIV total velocity data to obtain electroosmotic flow field velocities. Ensemble-averaged velocity field measurements for electroosmotic flow at the intersection of a cross-channel are presented.

3D Numerical Analysis of Joule Heating Effect on Electroosmotic Flow in Microchannels

2006 ◽  
Author(s):  
Reza Monazami ◽  
Shahrzad Yazdi ◽  
Mahmoud A. Salehi
Keyword(s):  
Electric Field ◽  
External Electric Field ◽  
Charge Distribution ◽  
Cross Section ◽  
Joule Heating ◽  
Electroosmotic Flow ◽  
Three Dimensional ◽  
Micro Channel ◽  
Heating Effect ◽  
Energy Equations

In this paper, a three-dimensional numerical model is developed to analyze the influence of the Joule heating on flow characteristics of an electroosmotic flow through square cross section micro-channels. The governing system of equations consists of three sets of equations: electric potential distribution, flow-field and energy equations. The solution procedure involves three steps. The net charge distribution on the cross section of the micro-channel is computed by solving two-dimensional Poisson-Boltzmann equation using the finite element method. Then, using the computed fluid’s charge distribution, the magnitude of the resulting body force due to interaction of an external electric field with the charged fluid elements is calculated along the micro-channel. Finally, three dimensional coupled Navier-Stokes and energy equations are solved by considering the presence of the electro-kinetic body forces and the volumetric heat generation due to Joule heating for three different external electric field strengths. The results reveal that flow patterns are significantly affected by temperature field distribution caused by Joule heating effect especially for high electric field strength cases.

scholarly journals Numerical Investigation of Nanostructure Orientation on Electroosmotic Flow

Micromachines ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 971
Author(s):  
An Eng Lim ◽  
Yee Cheong Lam
Keyword(s):  
Electric Field ◽  
Field Distribution ◽  
Applied Electric Field ◽  
Electroosmotic Flow ◽  
Electric Field Distribution ◽  
Flow Direction ◽  
Fluid Velocity ◽  
Orientation Angle ◽  
Dependent Behavior ◽  
Velocity Region

Electroosmotic flow (EOF) is fluid flow induced by an applied electric field, which has been widely employed in various micro-/nanofluidic applications. Past investigations have revealed that the presence of nanostructures in microchannel reduces EOF. Hitherto, the angle-dependent behavior of nanoline structures on EOF has not yet been studied in detail and its understanding is lacking. Numerical analyses of the effect of nanoline orientation angle θ on EOF to reveal the associated mechanisms were conducted in this investigation. When θ increases from 5° to 90° (from parallel to perpendicular to the flow direction), the average EOF velocity decreases exponentially due to the increase in distortion of the applied electric field distribution at the structured surface, as a result of the increased apparent nanolines per unit microchannel length. With increasing nanoline width W, the decrease of average EOF velocity is fairly linear, attributed to the simultaneous narrowing of nanoline ridge (high local fluid velocity region). While increasing nanoline depth D results in a monotonic decrease of the average EOF velocity. This reduction stabilizes for aspect ratio D/W > 0.5 as the electric field distribution distortion within the nanoline trench remains nearly constant. This investigation reveals that the effects on EOF of nanolines, and by extrapolation for any nanostructures, may be directly attributed to their effects on the distortion of the applied electric field distribution within a microchannel.

High-performance near-infrared photodetectors based on C3N quantum dots integrated with single-crystal graphene

2021 ◽  
Author(s):  
Yun Zhao ◽  
Xiaoqiang Feng ◽  
Menghan Zhao ◽  
Xiaohu Zheng ◽  
Zhiduo Liu ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Electric Field ◽  
Single Crystal ◽  
High Performance ◽  
Near Infrared ◽  
Fast Response ◽  
Local Electric Field ◽  
Infrared Photodetectors ◽  
Photocurrent Response

Employing C3N QD-integrated single-crystal graphene, photodetectors exhibited a distinct photocurrent response at 1550 nm. The photocurrent map revealed that the fast response derive from C3N QDs that enhanced the local electric field near graphene.

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