Goran Goranovic

PIV measurements in a microfluidic 3D-sheathing structure with three-dimensional flow behaviour

The design and production time for complex microfluidic systems is considerable, often up to several months. It is therefore important to be able to understand and predict the flow phenomena prior to design and fabrication of the microdevice in order to save costly fabrication resources. The structures are often of complex geometry and include strongly three-dimensional flow behaviour, which poses a challenge for the micro particle image velocimetry (micro-PIV) technique. The flow in a microfluidic 3D-sheathing structure has been measured throughout the volume using micro-PIV. In addition, a stereoscopic principle was applied to obtain all three velocity components, showing the feasibility of obtaining full volume mapping (x, y, z, U, V, W) from micro-PIV measurements. The results are compared with computational fluid dynamics (CFD) simulations.

The clogging pressure of bubbles in hydrophilic microchannel contractions

We present a theoretical and numerical study of the quasi-static motion of large wetting bubbles in microfluidic channels with contractions. In most cases the energy of a bubble increases when it is moved from a wide channel to a narrow one, and the bubble thus tends to clog the flow of the fluid. A certain pressure, the so-called clogging pressure, is needed to push the bubbles out of the contraction. However, we show that in the case of a hydrophilic channel contraction there exists a range of parameter values where the bubble actually gains energy by moving into the narrow part. For these specific cases we analyze how the clogging pressure depends on channel geometry, surface tension and contact angle. Based on our analysis we establish design rules for minimizing the clogging pressure of microchannel contractions.

A novel electro-osmotic pump design for nonconducting liquids: theoretical analysis of flow rate–pressure characteristics and stability

We present the design and theoretical analysis of a novel electro-osmotic (EO) pump for pumping nonconducting liquids. Such liquids cannot be pumped by conventional EO pumps. The novel type of pump, which we term the two-liquid viscous EO pump, is designed to use a thin layer of conducting pumping liquid driven by electro-osmosis to drag a nonconducting working liquid by viscous forces. Based on computational fluid dynamics, our analysis predicts a characteristic flow rate of the order nL/s/V and a pressure capability of the pump in the hPa/V range depending on, of course, achievable geometries and surface chemistry. The stability of the pump is analyzed in terms of the three instability mechanisms that result from shear-flow effects, electrohydrodynamic interactions and capillary effects. Our linear stability analysis shows that the interface is stabilized by the applied electric field and by the small dimensions of the micropump.

Theoretical analysis of the low-voltage cascade electro-osmotic pump

The recently published experimental results obtained by Takamura et al. [Y. Takamura, H. Onoda, H. Inokuchi, S. Adachi, A. Oki, Y. Horiike, in: J.M. Ramsey, A. van den Berg (Eds.), Proceedings of the μTAS 2001, Monterey, CA, USA, Kluwer Academic Publishers, Drodrecht, 2001, p. 230], on their low-voltage cascade electro-osmotic pump are analyzed using two different theoretical approaches. One is the semi-analytical equivalent circuit theory involving hydraulic resistances, pressures, and flow rates. The other is a full numerical simulation using computational fluid dynamics. These two approaches give the same results, and they are in good qualitative agreement with the published data. However, our theoretical results deviate quantitatively from the experiments. The reason for this discrepancy is discussed.

Dynamics of Bubbles in Microchannels

We present a thorough theoretical study of quasi-static motion and dynamics of bubbles in microchannels. We investigate the effects of geometry and surface physics on the behavior of bubbles, and we propose a set of design rules to minimize the clogging of the channels by bubbles.

The Low-Voltage Cascade EOF PUMP: Comparing Theory with Published Data

The recently published experimental results obtained by Takamura et al. [proc. Micro Total Analysis Systems 2001, p. 230–232 (2001)], on their low-voltage cascade electroosmotic pump are analyzed using two different theoretical approaches. One is the semi-analytical equivalent circuit theory involving hydraulic resistances, pressures, and flow rates. The other is a full numerical simulation using computational fluid dynamics. These two approaches give the same results, and they are in good qualitative agreement with the published data. However, our theoretical results deviate quantitatively from the experiments. The reason for this discrepancy is discussed.

Electroosmotically Driven Two-Liquid Viscous Pump for Nonconducting Liquids

A novel pump design relying on two-liquid viscous drag to pump nonconducting liquids is presented. A conducting pumping liquid driven by electroosmosis (EOF) drags a nonconducting working liquid by viscous forces. In particular liquids such as oil or ethanol, which normally cannot be moved by an EOF, can be pumped through the system. The pump is operated in the low-voltage regime. The flow-rate/pressure (Q-p) characteristic of the pump depends largely on achievable geometrical dimensions. This paper presents a complete theoretical and modeling study of the novel design.