Microchannels mixing

Due to the predominantly laminar flow present in microchannels, mixing in these devices is largely controlled by molecular diffusion. In the scale of dimensions considered here, i.e. channel widths/depths ranging from a few hundred micrometers to a few millimeters, the mixing process by molecular diffusion is extremely slow, since the mixing time is proportional to df/Dm, where di is the characteristic... 

Galbiati L, Andreini P (1992) Elow patterns transition for vertical downward two-phase flow in capUlary tubes. Inlet mixing effects. Int Comm Heat Mass Transfer 19 791-799 Garimella S, Sobhan C (2003) Transport in microchannels - a critical review. Ann Rev Heat Transfer 13 1-50... 

The fabricated microchannel plates were stacked together and tightened by end-plates to prevent the leak and mixing of gases as shown in Fig. 2. The dimensions of the reactor excluding fittings were about 60 mm x 40 mm x 3 mm respectively. 

H. H., Mixing processes in a zigzag microchannel finite element simulations and optical study. Anal. Chem. 74 (2002) 4279-1286. 

Meisel, I., Ehrhard, P., Simulation of electrically-excited flows in microchannels for mixing applications, in Proceedings of the 5th International Conference on Modeling and Simulation of Microsystems, San )uan, Puerto Rico, 22-25 April 2002, Computational Publications, Boston, pp. 62-65 (2002). 

For high-frequency measurements, normal photomultipliers are too slow, and microchannel plate photomultipliers are required. However, internal crosscorrelation is not possible with the latter and an external mixing circuit must be used. 

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-... 

Three sets of nanoflex valves are placed so as to control the connection between two sets of microchannels. One set of microchannels is dedicated to the reservoir solution and the other to the sample to crystallize. The first set of valves separates the two sets of microchannels (interface line), the second and the third (containment lines) hermetically seal the reservoir and sample solutions once they have been injected in the chip. A crystallization experiment proceeds as follows. First, pressure is applied to the interface line. Then the reservoir and sample solutions are injected. The two containment lines can then be pressurized while the interface line is relaxed to mix the solutions. The crystallization... 

In order to detect the analyte specifically, a complex has to be formed first. To this end, the revelation moiety (e.g. an enzyme-labelled antigen or antibody) is for instance incubated in the chip so as to bind to the analyte that has previously been captured within the microchannel. In another scheme, the analyte solution is first mixed with the revelation moiety, and the formed complex is then incubated in the chip in order to be captured on the bed of antibodies coating the walls of the micro-channel. After a washing step (to remove the excess affinity partner), the microchannel is filled with the substrate which shall thus react... 

For the small microchannel dimensions involved (Figure 7), conductive heat transfer plays an important role, augmenting the heat transfer coefficients by a factor of 5 or more to values in the vicinity of 700 W/m2K. This phenomenon is also responsible for good transverse mixing, counteracting the negative effects of laminar-flow profiles. 

The characteristics of electrokinetically controlled fluid flow in microchannel manifolds has been studied in a systematic way by Harrison and coworkers [28, 30]. An illustrative demonstration of the potential of this approach is shown in Fig. 2 for the controlled dilution of a fluorescein solution under voltage control. In parallel with a stepwise decrease of the potential applied to the fluorescein reservoir, a decrease of fluorescence signal downstream after the junction is visible in Fig. 2. As long as the ionic strength and pH in each supply channel is the same (same jieo), mass balance is automatically fulfilled, and the incoming flows at the intersection will be exactly balanced by the outgoing flow of the mixed components (otherwise, mass balance would be enforced by additional hydrodynamic or secondary internal flows). This way of mixing fluids was also... 

Mixing in a PMMA T-junction was achieved by chaotic advection in the channel with slanted grooves created by laser photoablation (see Figure 3.40) [193,257,470]. Mixing could also be achieved in a PDMS microchannel using square grooves in the channel bottom (see Figure 3.41) [471]. 

A 3D serpentine microchannel was fabricated on a Si-glass chip to enhance mixing by chaotic advection (see Figure 3.44). It was found that mixing in the 3-D channel was faster and was more uniform than in either a square wave channel or straight channel [477]. 

FIGURE 5.18 Illustration of the flow confinement concept. In microchannels, a sample flow is joined with a confinement flow (e.g., water or sample medium) in a perpendicular orientation. Under laminar flow conditions, no mixing occurs. The sample flow is confined into a thin layer of higher velocity. For immunoassay application, rabbit IgG is immobilized on a planar waveguide and Cy5-labeled anti-rabbit IgG is introduced as analyte in the sample flow [694]. Reprinted with permission from the American Chemical Society. 

In another report, Michaelis-Menten parameters of ALP have been obtained using a one-shot Lineweaver-Burk (reciprocal) plot. This can be achieved by simultaneously measuring the conversion of 12 independent concentrations of the substrate (4-methylumbelliferyl phosphate) created on-chip. The enzyme was streptavidin-conjugated ALP that was linked to biotinylated phospholipid bilayers coated inside PDMS microchannels. The blue fluorescence of the enzymatic product, 7-hydroxy-4-methyl coumarin, was measured [ 1043]. The surface-bound enzyme was found to have a lower (sixfold) turnover rate than the free enzyme in solutions. After diffusion mixing between two streams (substrate and buffer)... 

Lee, S., Kim, Y., Metering and mixing of nanoliter liquid in the microchannel networks driven by fluorocarbon surfaces and pneumatic control. Micro Total Analysis Systems, Proceedings 5th p,TAS Symposium, Monterey, CA, Oct. 21-25, 2001. Kluwer Academic Publishers, Dordrecht, the Netherlands, 2001, 205-206. 

Glasgow, I., Lieber, S., Aubry, N., Parameters influencing pulsed flow mixing in microchannels. Anal. Chem. 2004, 76, 4825-4832. 

---