Microchannel walls

To process the methanol and water mix, a CuZnAl catalyst was wash-coated onto the microchannel walls. The alumina was deposited by dipping the plates into a 20% alumina suspension, which also included a stabilizer and a binder. After any excess was wiped off, the plates were calcined at 600 °C for 1 h in air. Air was removed from the pores by placing the calcined plate in a vacuum. The alumina wash-... 

The PDMS-E described in the batch studies was used to mold reactors. These microreactors were fed the same 0.1 M urea solution as used in batch experiments. Reactors were operated for approx 1 hbefore acquiring operational data to reduce the effects of any loosely bound enzymes that may wash out from the surfaces of the microchannel walls. 

Figure 3.2 GPMR used for biocatalytic transformations with immobilized enzymes [22]. (a) the fully assembled microreactor, (b) microstructured multichannel plate, and (c) electron micrograph of the wash-coat layer of y-aluminum oxide covering the microchannel walls.

SAMs on microchannel walls have been studied for surface properties in microreactors,59 to control surface wetting,60 to create zones for specific immobilization of proteins and biomolecules,61 and to conduct catalytic reactions.62 And a pH sensing monolayer confined to a glass microchannel has been reported by our group.32... 

Another interesting example was provided by Teplyakov et al. [6] at the last EuroMembrane Congress in Taormina, in September 2006. The authors deal with processes using porous ceramics with catalytic coating in microchannel walls. This... 

D. C. Tretheway and C. D. Meinhart, Apparent fluid slip at hydrophobic microchannel walls, Phys. Fluids 14, L9-L12 (2002) Chang-Hwan Choi, J. A. Westin, and K. S. Breuer, Apparent slip flows in hydrophilic and hydrophobic microchannels, Phys. Fluids 15, 2897-902 (2003). 

A method for coating microchannel walls with layers as thick as 25 pm was developed by Stefanescu et al. [181]. The microreactor was built from FeCrAl (Aluchrom ). The metal surface was first chemically treated in several steps and afterward annealed at 1200 °C for 1 h to trigger the segregation of aluminum and the formation of an alumina layer on the metallic surface. An alumina washcoat was subsequently deposited from a slurry onto the microstructure and characterized by various physical methods. The authors varied the properties such as viscosity, particle size, and pH of the slurry. Acrylic acid, a component used as dispersant and binder, was found to be particularly important for the adhesion of the alumina layer. 

In this lecture, the effects of the abovementioned dimensionless parameters, namely, Knudsen, Peclet, and Brinkman numbers representing rarefaction, axial conduction, and viscous dissipation, respectively, will be analyzed on forced convection heat transfer in microchannel gaseous slip flow under constant wall temperature and constant wall heat flux boundary conditions. Nusselt number will be used as the dimensionless convection heat transfer coefficient. A majority of the results will be presented as the variation of Nusselt number along the channel for various Kn, Pe, and Br values. The lecture is divided into three major sections for convective heat transfer in microscale slip flow. First, the principal results for microtubes will be presented. Then, the effect of roughness on the microchannel wall on heat transfer will be explained. Finally, the variation of the thermophysical properties of the fluid will be considered. 

Countercurrent microchannel extraction has been performed by chemical modification of the microchannel wall with octadecylsilane groups on the bottom of the glass plate. Additionally, the two phases flowed in separate microchannels and crossed each other at an angle. If the correct flow rate and pressure differences were maintained, phase separation would occur [209]. 

Minimal adsorption to or nonspecific interaction with microchannel walls... 

Fig. 2.8 Smectic 8CB confined inside a closed rectangular microchannel with mixed anchoring conditions [47], Three microchannel walls impose homeotropic anchoring, while the fourth wall imposes planar anchoring as shown in the schematic illustration in (e). The microchannels are 20 (a), 10 (b), 60 (c) and 40 (d) pm wide and 3.8 (a, b), 10 pm (c, d) deep. Scale bars are 5 pm in (a) and (b) and 10 pm in (c) and (d). Reprinted with permission [47]. Copyright 2006, American Chemical Society...

OTS-coated) microchannel wall and no slip for a hydrophilic surface. Cheng and Giordano [2] reported pressure-driven flow of several classical fluids (hexane, decane, hexadecane, and silicon oil) through lithographically produced channels. The results for water agree well with the theoretical prediction of no-slip BC, for channel height as small as 40 nm. However, for hexane, decane, hexadecane, and silicone oil, slip flow is observed when channel separation is reduced below about 100 nm (Fig. 3). 

Tretheway D, Meinhart C (2002) Apparent fluid slip at hydrophobic microchannel walls. Phys Fluids 14 L9-L12... 

The particle of Dp = 20 pm suspended in a microchannel. The zeta potential on the microchannel wall is —15 mV. A uniform zeta potential of —60 mV on the nonconducting surfaces of nonconducting sphere and heterogeneous particle. The DC electric field of E = 30 V/cm is applied from left to write. The electroosmotic flow is from left to right... 

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