Haiqing Gong

Development of a levitated micromotor for application as a gyroscope

A miniature rotating gyroscope is described, in which a 0.5 mm aluminium rotor is levitated, rotated, and constrained by a combination of electromagnetic induction and electrostatic forces generated from a unique planar coil design. Integrated into the planar coil design are the sense electrodes that allow the angular-rate of the device to be measured about two orthogonal axes, and acceleration along the third, producing a multimode inertial sensor. In this paper, the results of electrostatic, rotation, and thermal measurements, together with the finite element and analytical modelling are presented. Excellent agreement is found between the electromagnetic and electrostatic experimental measurements and modelling. A simple viscous drag model is proposed to explain the experimental rotational measurements and its limitations are discussed.

Joule heating and its effects on electroosmotic flow in microfluidic channels

Joule heating is resulted from inevitable volumetric heating when an electric field is applied across conducting media and it would impose limitations to the performance of electrokinetic microfluidic devices. In this paper, the Joule heating and its effects on electroosmotic flow (EOF) in PDMS microfluidic channels are reported. 3D numerical simulation of the Joule heating induced temperature field and its effects on the EOF and electrophoretic transport of solutes in microchannels was performed. Experiments were carried out to verify the proposed models and the developed numerical code. A Rhodamine B based thermometry technique was used to measure the solution temperature distributions in PDMS microfluidic channels. The micro particle image velocimetry (micro-PIV) technique was used to characterize the velocity profiles of the EOF under the influence of Joule heating. The numerical simulations were compared with the experimental results, and reasonable agreement is 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; the EOF velocity exhibits a concaved shape in the hydrodynamically developing region and a convex (parabolic) pattern in the fully developed region.

On Electrokinetic Mass Transport in a Microchannel With Joule Heating Effects

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

Joule Heating Induced Thermal and Hydrodynamic Development in Microfluidic Electroosmotic Flow

Joule heating is present in electrokinetically driven flow and mass transport in microfluidic systems. Specifically, in the cases of high applied voltages and concentrated buffer solutions, the thermal management may become a problem. In this study, a 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. These governing equations are coupled through temperature-dependent phenomenological thermal-physical coefficients, and hence they are numerically solved using a finite-volume based CFD technique. A comparison has been made for the results of the ionic concentration distributions and the electroosmotic flow velocity and temperature fields obtained from the Nernst-Planck equation and the Boltzmann equation. The time and spatial developments for both the electroosmotic flow fields and the Joule heating induced temperature fields are presented. In addition, sample species concentration is obtained by numerically solving the mass transport equation, taking into account of the temperature-dependent mass diffusivity and electrophoresis mobility. The results show that the presence of the Joule heating can result in significantly different electroosomotic flow and mass species transport characteristics.Copyright

Electroosmotic Flow and Mass Species Transport in a Microcapillary Under Influences of Joule Heating

This study presents a numerical analysis of Joule heating effect on the electroosmotic flow and species transport, which has a direct application in the capillary electrophoresis based BioChip technology. A rigorous mathematic model for describing the Joule heating in an electroosmotic flow including Poisson-Boltzmann equation, modified Navier-Stokers equations and energy equation is developed. All these equations are coupled together through the temperature-dependent parameters. By numerically solving aforementioned equations simultaneously, the electroosmotic flow field and the temperature distributions in a cylindrical microcapillary are obtained. A systematic study is carried out under influences of different geometry sizes, buffer solution concentrations, applied electric field strengths, and heat transfer coefficients. In addition, sample species transport in a microcapillary is also investigated by numerically solving the mass transfer equation with consideration of temperature-dependant diffusion coefficient and electrophoresis mobility. The characteristics of the Joule heating, electroosmotic flow, and sample species transport in microcapillaries are discussed. The simulations reveal that the presence of the Joule heating could have a great impact on the electroosmotic flow and sample species transport.Copyright