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

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.