Microchannels cross-section

An important advantage of the use of EOF to pump liquids in a micro-channel network is that the velocity over the microchannel cross section is constant, in contrast to pressure-driven (Poisseuille) flow, which exhibits a parabolic velocity profile. EOF-based microreactors therefore are nearly ideal plug-flow reactors, with corresponding narrow residence time distribution, which improves reaction selectivity. 

Figure 6.2 SEM images of the microchannel cross-section with and without annealing treatment step. (A) Without treatment, xlOO magnification 1, top cyclo-olefin substrate 2, bottom cyclo-olefin substrate 3, separation line. (B) Without treatment, x500 magnification. (C) With treatment, xlOO magnification. (D) With treatment, x500 magnification. (From ref. 19.)...

Microreactor chips were mounted on a dedicated holder (Figure 9.4a and b), placed on the Nanospray interface of the mass spectrometer using a metal plate. Solutions were introduced on-chip via fused silica capillaries (o.d. = 360 pm) of 100, 40 or 20 pm (i.d.), depending on the microchannel cross-sectional... 

FIGURE 38.19 Two 100 aM sample electropherograms of ITP/CE separation of Alexa Fluor 488 (the peaks near 73.5 s) and Bodipy (peaks near 76.5 s). A glass microchip (microchannel cross-sectional dimensions are 50 xm wide and 20 p.m deep) and 60x water immersion objective (N.A. = 0.9) were used. The detector was located 30 mm downstream of the injection region. 

Fruther investigations are required in order to highlight the roles of wall-fluid conjugate heat transfer, temperature-dependent fluid properties (i.e., viscosity), rarefaction, compressibility, and axial variation of the zeta potential in electroosmotic flows in developing flows for the most common microchannel cross-sectional geometries. 

A drawback of the strategy reported here to reduce fluid flow rate in CZE systems is its tendency to increase the broadening of sample bands. Such broadening occurs due to nonuniformity in the pressure-driven flow profile and is known to scale directly with the shortest lateral dimension of the analysis column [3]. However, because diffusion across microchannel cross sections tends to be rapid, flow dispersion in the reported microfluidic... 

The hydrodynamic entrance length is also influenced by the cross-sectional geometry of the microchannel. In order to take into account the role played by the geometry of the microchannel cross section on the hydrodynamic entrance length, Eq. 5 can be replaced by the following approximate equation ... 

The fuUy developed values of Pmax, and/Rofd can be found in pressure-driven singlephase liquid flow for the most conmum microchannel cross sections. 

In the Hausen correlation, the Nusselt number is calculated as a sum of two terms the first term (Nu) is the fully developed value of the Nusselt number its value can be found in convective heat transfer in microchannels for the most common microchannel cross sections. The second term takes into account the effects of... 

Secondly, the effect of the wall-fluid conjugate heat transfer tends to be very strong for moderate Reynolds numbers especially in the entrance region of a microchannel where the wall heat flux distribution becomes nommiform (see Fig. 6) even for a uniformly heated microchannel (H boundary condition). For these reasons, further investigations on the combined effect of the conjugate heat transfer and of the temperature-dependent fluid properties (i.e., viscosity) on the mean value of the Nusselt number in the entrance region for the most common microchannel cross-sectional geometries can be considered mandatory. 

Particle/cell manipulation aims to position the particles/cells at a certain location inside the chaimel. The purpose is not necessarily to separate these cells but to control their location. Controlling the location of cells is particularly important for cell washing and cell concentration purposes. A common target in these studies is to position the cells in the pressure node locations. In several studies, the particles are positioned at pressure node locations successfully [3]. In a rather recent study, Glynne-Jones et al. [4] were able to position the microparticles to any location in the microchannel cross section by feeding a mode-switched signal to the piezoelectric element. 

Mixing visualization using 1 gM fluorescein solution in mixer with breakup obstructions at increasing distances downstream. Fluorescein solution is flowing in the upper portion of the images (pseudo colored green) and water in the lower portion. Pixel intensity line scans across the microchannel cross-section at (b) the entrance and (c) 5 mm downstream [22]... 

The model for the pressure drop analysis is depicted in Fig. 9 in which multiple microchannels with an abrupt entrance and exit are shown. The equations to be presented in this section apply to this model and are not restricted to a particular geometry of the microchannel cross section. 

Apart from the microchannel cross-section, the impact of non-straight charmels is crucial, especially for mixing applications, where serpentine channels have been shown to break symmetry and enhance mixing in bubbles [106]. Note that this enhanced mixing is due to chaotic advection in Stokes flow. Dean vortices, i.e. secondary flow patterns due to centrifugal inertia, are typically not a problem in low-inertia (Re< 1) microfluidic applications. 

A second important flow pattern for conducting chemical reactions is segmented flow. In such flows, segments of a disperse phase extend over almost the entire microchannel cross section dh- Dispersed fluid segments can be either droplets or bubbles. Although we focus on bubbles in this section, most of the analysis is directly... 

Consider the bowed microchannel cross-section depicted in Fig. 7a with a depth d and width Tk. The easiest way of... 

For Newtonian laminar flows these parameters depend on the geometry of the microchannel cross-section only. 

Figure 9.5 Flow pattern of a falling film in falling film microreactor (microchannel cross-section 1000pm X 300pm liquid 110ppm SLS solution), (a) Corner rivulet flow (Ql = 2 ml/min) (b) falling film flow with dry...

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