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

The deflocculation of kaolin suspensions : the effect of various electrolytes

The deflocculation effect of conventional additives to kaolin suspensions is evaluated from the results standard rheological measurements. Several widely used electrolytes (NaOH, Na2C03, Na2Si03, SHMP = sodium hexametaphosphate, and CMC = sodium salts of carboxymethylcellulose) have been tested. The optimal concentrations of these deffloculants, in respect to reaching the maximum reduction of initial suspension viscosity, are found. The stability of deflocculated kaolin suspensions against sedimentation is evaluated and different aspects of the observed flow enhancement discussed. Inorganic electrolytes are found to be more effective in viscosity reduction, but on the other hand, low-molecular organic CMC additives produce more stable final suspensions.Czech Science Foundation GACR through the contract P101/12/058

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

Efficient analysis of high impedance metasurface with an interstitial-currents approach

An efficient surface integral equation approach is proposed for the electromagnetic analysis of multilayered doubly periodic arrays of high impedance surfaces. It makes use of equivalent electric and magnetic currents on the interfaces between layers. Interfaces may be physical or fictitious. In the case where the interfaces are physical, the background medium in a given layer can be treated as a homogeneous unbounded medium for which the computation of Green’s function for an infinite doubly periodic array is sufficient. The resulting method-of-moments matrix has a block-tridiagonal structure, which leads to a computational complexity proportional to the number of layers for both matrix filling and solution. The numerical results from a two-layer high impedance surface prove the accuracy and efficiency of the interstitial-currents approac