-
[show abstract]
[hide abstract]
ABSTRACT: Temperature gradient focusing (TGF) is a recently developed technique for spatially focusing and separating ionic analytes in microchannels. The temperature gradient required for TGF can be generated either by an imposed temperature gradient or by Joule heating resulting from an applied electric field that also drives the flow. In this study, a comprehensive numerical model describing the Joule heating induced temperature development and TGF 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 the valid mathematical model presented in this study.
Electrophoresis 04/2008; 29(5):1006-12. · 3.30 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Joule heating is inevitable when an electric field is applied across a conducting medium. It would impose limitations on the performance of electrokinetic microfluidic devices. This article presents a 3-D mathematical model for Joule heating and its effects on the EOF and electrophoretic transport of solutes in microfluidic channels. The governing equations were numerically solved using the finite-volume method. Experiments were carried out to investigate the Joule heating associated phenomena and to verify the numerical models. A rhodamine B-based thermometry technique was employed to measure the solution temperature distributions in microfluidic channels. The microparticle image velocimetry technique was used to measure the velocity profiles of EOF under the influence of Joule heating. The numerical solutions were compared with experimental results, and reasonable agreement was found. It is found that with the presence of Joule heating, the EOF velocity deviates from its normal "plug-like" profile. The numerical simulations show that Joule heating not only accelerates the sample transport but also distorts the shape of the sample band.
Electrophoresis 03/2006; 27(3):628-39. · 3.30 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Microfluidic concentration of sample solutes is achieved by 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. Scaling analysis is conducted to estimate time scales so as to simplify the proposed mathematical model. Numerical computations are performed to obtain the temperature, velocity and sample concentration distributions which allow us to reveal the insightful TGF mechanisms. Experiments are carried out to study the effects of applied voltage, buffer concentration, and channel size on the TGF of sample solutes in both PSMD/Glass and PDMS/PDMS microdevices. It is found that the focusing location of samples varies with these experimental parameters, and this scenario can be explained using our present numerical model. In addition, the experimental parametric effects are summarized using a dimensionless Joule number that is introduced in this study. The Joule number effect in the PDMS/PDMS microdevice is compared with that in the PDMS/Glass microdevice. A more than 450-fold concentration enhancement is obtained within 75 s in the PDMS/PDMS microdevice. Overall, the numerical simulations are found in reasonable agreement with the experimental results.
International Journal of Heat and Mass Transfer.
-
Gongyue. Tang
[show abstract]
[hide abstract]
ABSTRACT: Owing to numerous merits including improved resolution, increased throughput, reduced analysis time and decreased sample consumption, the microfluidic devices have found a wide spectrum of applications in the biomedical areas such as DNA sequencing, nucleic acid analysis, enzyme assays, immunoassays, etc. In microfluidic devices, electrokinetic transport, which in principle exploits two driving mechanisms - electrophoresis and electroosmosis, is used extensively to control liquid buffer flow and manipulate samples of nano/pico-liter volumes. It is known that the presence of Joule heating imposes limitations to the performance of electrokinetic transport. However, systematic investigations of the Joule heating and its effects on electroosmotic flow and electrokinetic mass transport based on the rigorous mathematical models still remain limited. In light of this, this dissertation provides a fundamental, systematic and in-depth exploration on the Joule heating and its effect on the electrokinetic transport in microfluidic systems. DOCTOR OF PHILOSOPHY (MPE)
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, the studies of the Joule heating and its effects on electrokinetic transport (i.e., electroosmotic flow and electrophoretic transport) of solutes in rectangular microchannels are reported. 3D mathematical models describing the Joule heating induced temperature field and its effects on the EOF and electrophoretic transport of solutes in microchannels are developed, and the coupled governing equations are solved numerically using the finite volume based CFD technique. In addition, experiments are carried out to investigate the Joule heating associated phenomena and to verify the numerical models. A Rhodamine B based thermometry technique was employed to measure the solution temperature distributions in PDMS microfluidic channels. The micro particle image velocimetry (micro-PIV) technique was used to measure the velocity profiles of the EOF under the influence of Joule heating. The numerical solutions were compared with experimental results, and reasonable agreement was found. Both the numerical simulations and the experimental results show that the presence of the Joule heating causes the EOF velocity to deviate from its normal “plug-like” profile; moreover, the numerical simulations show that Joule heating not only accelerates the sample transport but also distorts the shape of the sample band. The simulation results also reveal that the Joule heating and its effects in a PDMS/PDMS channel is more significant than those in a glass/PDMS channel.
Sensors and Actuators A: Physical.
