Elliptical Microchannels Research Articles

Electro-osmotic heat transfer in elliptical microchannels under H1 boundary condition

This work presents a detailed numerical analysis of electro-osmotic flows inside silicon microchannels characterized by an elliptical cross-section. A finite element method is used to solve the governing equations and perform an extensive parametric study. Particular attention is given to the effect of the aspect ratio of the elliptical cross-section, the electro-kinetic diameter, the ratio of the Joule heating to the imposed wall heat flux on the dynamic and thermal behavior of electro-osmotic flows in the case of H1 boundary conditions. The analysis presented in this paper can be useful to optimize design and thermal performances of silicon micro heat sinks based on electro-osmotic flows.Results point out that as the electro-kinetic diameter increases, the influence of the Joule heating on the temperature distribution becomes less relevant. This trend becomes more pronounced as the aspect ratio increases. Numerical results also show that an increment of the electro-kinetic diameter leads to an enhancement of the convective heat transfer.A comparison between numerical results obtained for electro-osmotic flows through elliptical and rectangular geometries is finally shown and discussed. Such comparison highlights that rectangular microchannels have better performances at small values of the aspect ratio, while elliptical microchannels are more effective for greater values of aspect ratio.

Numerical analysis of electro-osmotic flows through elliptic microchannels

This work presents a comprehensive numerical analysis of electro-osmotically driven flows inside microchannels characterized by an elliptic cross-section. The mathematical model takes into account the presence of an opposing pressure gradient to correctly reproduce the operating conditions of pumps. The dynamical features are analyzed for isothermal flows in the fully developed region. Characteristic curves that relate the volumetric flow rate and the pressure head are presented with respect to all the non-dimensional parameters that influence the behavior of combined electroosmotic/ pressure-driven flows, i.e., the aspect ratio of the cross-section, the electrokinetic diameter, the non-dimensional zeta-potential and the ratio of the pressure force to the electric force. Such numerical results are also compared with two existing correlations for microchannels with rectangular or trapezoidal cross-sections, that assess both volumetric flow rate and pressure head. The comparison highlights that the correlation for the volumetric flow rate works perfectly also for this kind of geometry, while a correction is proposed for the pressure head estimate, in order to extend the validity of the original correlation to elliptic microchannels.

Micro- and nanostructures inside sapphire by fs-laser irradiation and selective etching

The fabrication of microchannels and self-assembled nanostructures in the volume of sapphire was performed by femtosecond laser irradiation followed by chemical etching with aqueous solution of HF acid. Depending on the focusing conditions self-organized nanostructures or elliptical microchannels are produced. While the dimensions in two directions are on a micro- respectively nanoscale, feature lengths of up to 1 mm are achieved. This comes out to aspect ratios of more than 1000. This fabrication technique is potentially usable for photonic crystal based integrated optical elements or microfluidic devices for applications in life science, biology or chemistry.

Slip flow in elliptic microchannels

Microscale fluid dynamics has received intensive interest due to the emergence of Micro-Electro-Mechanical Systems (MEMS) technology. When the mean free path of the gas is comparable to the channel's characteristic dimension, the continuum assumption is no longer valid and a velocity slip may occur at the duct walls. The elliptic cross-section is one useful channel shape that may be produced by microfabrication. The elliptic microchannels have potential practical applications in MEMS. Slip flow in elliptic microchannels has been examined and a detailed theoretical analysis has been performed. A solution is obtained using elliptic cylinder coordinates and the separation of variables method. A simple model is developed for predicting the Poiseuille number in elliptic microchannels for slip flow. The developed model may be used to predict mass flow rate and pressure distribution of slip flow in elliptic microchannels.

Electrokinetic flow in an elliptic microchannel covered by ion-penetrable membrane

The electrokinetic flow of an electrolyte solution in an elliptical microchannel covered by an ion-penetrable, charged membrane layer is examined theoretically. The present analysis extends previous results in that a two-dimensional problem is considered, and the system under consideration simulates the flow of a fluid, for example, in a microchannel of biological nature such as vein. The electroosmostic volumetric flow rate, the total electric current, the streaming potential, and the electroviscous effect of the system under consideration are evaluated. We show that, for a constant hydraulic diameter, the variations of these quantities as a function of the aspect ratio of a microchannel may have a local minimum or a local maximum at a medium level of ionic strength, which depends on the thickness of the membrane layer. For a constant cross-sectional area, the electroosmostic volumetric flow rate, the total electric current, and the streaming potential increase monotonically with the increase in the aspect ratio, but the reverse is true for the electroviscous effect.

Liquid core modal interferometer integrated with silica waveguides

An integrated structure is demonstrated as a refractive index sensor. The structure consists of a liquid-filled elliptical microchannel embedded in silica glass and integrated with waveguides. The microchannel features entry points that are open to the top surface of the device and distinct from the optical input. The structure allows light to couple from a solid-core input waveguide to the liquid-core waveguide formed by the microchannel, and back to a solid-core output waveguide. Bimodal interference allows the structure to be sensitive to the refractive index of the liquid, with a full beat corresponding to a refractive index change of /spl sim/10/sup -4/. The structure allows the direct integration of optical fluids with silica waveguides for sensing and optical processing applications.

Electrokinetic Flow through an Elliptical Microchannel: Effects of Aspect Ratio and Electrical Boundary Conditions

The electrokinetic flow of an electrolyte solution through an elliptical microchannel is studied theoretically. The system under consideration simulates the flow of a fluid, for example, in vein. We show that, for a constant cross-sectional area, both the electroosmotic volumetric flow rate and the streaming potential increase monotonically with an increase in the aspect ratio, and both the total electric current and the electroviscous effect may exhibit a local minimum as the aspect ratio varies. Also, for a constant average potential on the channel wall, the difference between the results based on three kinds of boundary conditions, which include constant surface charge, constant surface potential, and charge-regulated surface, is inappreciable if the hydraulic diameter is larger than 1 μm.