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.

Microfluidic concentration enhancement of bio-analyte by temperature gradient focusing via Joule heating by DC plus AC field: A numerical approach

2021 ◽  
pp. 1-17
Author(s):  
Amitava Dutta ◽  
Apurba Kumar Santra ◽  
Ranjan Ganguly
Keyword(s):  
Temperature Gradient ◽  
Joule Heating ◽  
Phosphate Buffer ◽  
Phosphate Buffer Solution ◽  
Numerical Approach ◽  
High Concentration ◽  
Buffer Solution ◽  
Temperature Gradient Focusing ◽  
Ac Field ◽  
Target Analyte

Abstract We present a detailed numerical analysis of electrophoresis induced concentration of a bio-analyte facilitated by temperature gradient focusing in a phosphate buffer solution via Joule heating inside a converging-diverging microchannel. The purpose is to study the effects of frequency of AC field and channel width variation on the concentration of target analyte. We tune the buffer viscosity, conductivity and electrophoretic mobility of the analyte such that the electrophoretic velocity of the analyte locally balances the electroosmotic flow of the buffer, resulting in a local build-up of the analyte concentration in a target region. An AC field is superimposed on the applied DC field within the microchannel in such a way that the back pressure effect is minimized, resulting in minimum dispersion and high concentration of the target analyte. Axial transport of fluorescein-Na in the phosphate buffer solution is controlled by inducing temperature gradient through Joule heating. The technique leverages the fact that the buffer's ionic strength and viscosity depends on temperature, which in turn guides the analyte transport. A numerical model is proposed and a finite element-based solution of the coupled electric field, mass, momentum, energy and species equations are carried out. Simulation predict peak of 670-fold concentration of fluorescein-Na is achieved. The peak concentration is found to increase sharply as the channel throat width, while the axial spread of concentrated analyte increases at lower frequency of AC field. The results of the work may improve the design of micro concentrator.

Concentration of Samples in Microfluidic Structure Using Joule Heating Effects

2009 ◽  
Author(s):  
Zhengwei Ge ◽  
Chun Yang
Keyword(s):  
Mathematical Model ◽  
Joule Heating ◽  
Electroosmotic Flow ◽  
Scaling Analysis ◽  
Analyte Concentration ◽  
Governing Equations ◽  
Sample Concentration ◽  
Heating Effects ◽  
Concentration Enhancement ◽  
The Mathematical Model

Microfluidic concentration is achieved using temperature gradient focusing (TGF) in a microchannel with a step change in cross-section. A mathematical model is developed to describe the complex TGF processes. The proposed mathematical model includes a set of governing equations for the applied electric potential, electroosmotic flow field, Joule heating induced temperature field, and sample analyte concentration distributions as well. Scaling analysis was conducted to estimate time scales so as to simplify the mathematical model. Numerical computations were performed to obtain the temperature, velocity and sample concentration distributions. 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 was introduced in this study. In addition, Joule number effect in the 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. Overall, the numerical simulations were found in a reasonable agreement with the experimental results.

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.

scholarly journals Joule heating effects on electroosmotic flow in insulator-based dielectrophoresis

2011 ◽  
pp. n/a-n/a ◽  
Author(s):  
Sriram Sridharan ◽  
Junjie Zhu ◽  
Guoqing Hu ◽  
Xiangchun Xuan
Keyword(s):  
Joule Heating ◽  
Electroosmotic Flow ◽  
Heating Effects

Joule Heating Induced Temperature Gradient Focusing in a Microfluidic Channel With a Sudden Change in Cross Section

2008 ◽  
Author(s):  
Gong Yue Tang ◽  
Chun Yang
Keyword(s):  
Temperature Gradient ◽  
Joule Heating ◽  
Stokes Equations ◽  
Sudden Change ◽  
Microfluidic Channel ◽  
Navier Stokes ◽  
Governing Equations ◽  
Temperature Gradient Focusing ◽  
Poisson Boltzmann Equation ◽  
Energy Equations

Temperature gradient focusing is a recently developed technique for spatially focusing and separating ionic analytes in microchannels. The temperature gradient required for temperature gradient focusing can be generated either by an imposed temperature gradient or by Joule heating resulted from an applied electric field that also drives buffer flow. In this study, a numerical model describing the Joule heating induced temperature development and temperature gradient focusing is developed. The model consists of a set of governing equations including the Poisson-Boltzmann equation, the Laplace equation, the Navier-Stokes equations, the energy equations and the mass transport equation. As the thermophysical and electrical properties including the liquid dielectric constant, viscosity and electric conductivity are temperature-dependent, these governing equations are coupled, and therefore the coupled governing equations are solved numerically by using a CFD based numerical method. The numerical simulations agree well with the experimental results, suggesting that the valid mathematical model presented in this study.

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