4 research outputs found
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Electrodiffusion Method of Near-Wall Flow Diagnostics in Microfluidic Systems
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The electrodiffusion technique has been mostly used for the near-wall flow diagnostics on large
scales. A novel technique for fabrication of plastic microfluidic systems with integrated metal
microelectrodes (called technique of sacrificed substrate) enables us to produce microfluidic devices with
precisely shaped sensors for wall shear stress measurements. Several micrometer thick gold sensors built-in a
plastic substrate exhibit good mechanical resistance and smoothness. Proper functioning of prepared chips
with microsensors has been first tested in various calibration experiments (polarization curve, sensor
response to polarization set-up, steady flow calibration, temperature dependence of diffusivity). Our first
results obtained for separating/reattaching flow behind a backward-facing step and for gas-liquid Taylor flow
in microchannels then demonstrate its applicability for the detection of near-wall flow reversal, the
delimitation of flow-recirculation zones, and the determination of wall shear stress response to moving
bubbles. Other applications of these sensors in microfluidics (e.g. characterization of liquid films, capillary
waves, bubbles or drops) can be also envisaged
Deflocculation of kaolin suspensions - The effect of various electrolytes
Viscosity reduction of aqueous kaolin suspensions by conventional additives (deflocculation) is studied, using standard viscosity measurements. Apparent viscosity at 100 s-1, and flow behavior index n give complex information about changes of viscosity and flow character of deflocculated suspensions. Several widely used deflocculants - electrolytes and polyelectrolytes - are tested in a wide range of concentrations. The optimum concentrations of these deflocculants, which result in minimum apparent viscosity of suspension, are found. Sedimentation stability of deflocculated suspensions is monitored. Inorganic electrolytes are found to be more effective in viscosity reduction. On the other hand, low-molecular-weight polyelectrolytes produce more stable final suspensions.The support by Czech Science Foundation GACR through the contract P101/12/0585 is gratefully acknowledged
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Characterization of fluid flow in a microchannel with a flow disturbing step
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The flow around a flow-disturbing step in a rectangular microchannel is studied by measuring the
wall shear rate along the channel, using the electrodiffusion technique and by determining the velocity field
using the -PIV method. A parametric study based on the Design of Experiments (DOE) and the Response
Surface Methodology (RSM) was then performed, and the effect of key design parameters on the flow characteristics
was numerically investigated using CFD simulations. The computational results are in excellent agreement
with the corresponding experimental ones. The CFD simulations cover both the laminar and the turbulent
flow regime. It was revealed that in both flow regimes the step height has a major influence on the recirculation
length. However, the Reynolds number (Re) value affects the recirculation length only in the laminar region,
while the step length seems to have no significant effect compared to the Re and the step height. Finally, new
correlations are proposed predicting the length of the bottom recirculation zone with reasonable accuracy and
can be used as rough guidelines for the design of microdevices