In this review we discuss the state of the art of the optical whole-field velocity measurement technique micro-scale Particle Image Velocimetry (µPIV). µPIV is a useful tool for fundamental research of microfluidics as well as for the detailed characterization and optimization of microfluidic applications in life science, lab-on-a-chip, biomedical research, micro chemical engineering, analytical chemistry and other related fields of research. An in depth description of the µPIV method is presented and compared to other flow visualization and measurement methods. An overview of the most relevant applications is given on the topics of near-wall flow, electrokinetic flow, biological flow, mixing, two-phase flow, turbulence transition and complex fluid dynamic problems. Current trends and applications are critically reviewed. Guidelines for the implementation and application are also discussed.

Micro-Particle Image Velocimetry (microPIV): recent developments, applications, and guidelines.

Electrophoretic separations on microfluidic chips

Electrokinetic flow is an efficient means to manipulate liquids and samples in lab-on-a-chip devices. It has a number of significant advantages over conventional pressure-driven flow. However, there exists inevitable Joule heating in electrokinetic flow, which is known to cause temperature variations in liquids and draw disturbances to electric, flow and concentration fields via temperature-dependent material properties. Therefore, both the throughput and the resolution of analytic studies performed in microfluidic devices are affected. This article reviews the recent progress on the topic of Joule heating and its effect in electrokinetic flow, particularly the theoretical and experimental accomplishments from the aspects of fluid mechanics and heat/mass transfer. The primary focus is placed on the temperature-induced flow variations and the accompanying phenomena at the whole channel or chip level.

Joule heating in electrokinetic flow.

The Joule heating (JH) is a ubiquitous phenomenon in electrokinetic flow due to the presence of electrical potential gradient and electrical current. JH may become pronounced for applications with high electrical potential gradients or with high ionic concentration buffer solutions. In this review, an in-depth look at the effect of JH on electrokinetic processes is provided. Theoretical modeling of EOF and electrophoresis (EP) with the presence of JH is presented and the important findings from the previous studies are examined. A numerical study of a fused-silica capillary PCR reactor powered by JH is also presented to extend the discussion of favorable usage of JH.

Effect of Joule heating on electrokinetic transport.

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.

Assessment of Joule heating and its effects on electroosmotic flow and electrophoretic transport of solutes in microfluidic channels.

Joule heating is present in electrokinetic transport phenomena, which are widely used in microfluidic systems. In this paper, a rigorous mathematical model is developed to describe the Joule heating and its effects on electroosmotic flow and mass species transport in microchannels. The proposed model includes the Poisson equation, the modified Navier−Stokes equation, and the conjugate energy equation (for the liquid solution and the capillary wall). Specifically, the ionic concentration distributions are modeled using (i) the general Nernst−Planck equation and (ii) the simple Boltzmann distribution. The relevant governing equations are coupled through the temperature-dependent solution dielectric constant, viscosity, and thermal conductivity, and, hence, they are numerically solved using a finite-volume-based CFD technique. The applicability of the Nernst−Planck equation and the Boltzmann distribution in the electroosmotic flow with Joule heating has been discussed. The results of the time and spatial dev...

Modeling of Electroosmotic Flow and Capillary Electrophoresis with the Joule Heating Effect: The Nernst−Planck Equation versus the Boltzmann Distribution

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.

Joule heating and its effects on electrokinetic transport of solutes in rectangular microchannels

We present a numerical analysis of electrokinetic mass transport in a microchannel with Joule heating effects. A nonuniform electric field caused by the presence of the Joule heating is considered in the model development. Numerical computations for electrokinetic mass transport under Joule heating effects are carried out using the Crank-Nicolson scheme of second-order accuracy in space and time for two different cases: (i) the translating interface and (ii) the dispersion of a finite sample plug

Cheekiong Chai

Papers

Modeling of Electroosmotic Flow and Capillary Electrophoresis with the Joule Heating Effect: The Nernst−Planck Equation versus the Boltzmann Distribution

Joule heating and its effects on electrokinetic transport of solutes in rectangular microchannels

On Electrokinetic Mass Transport in a Microchannel With Joule Heating Effects