Microfluidic bends

Despite the fact that the pressure seems to act purely to open the crack, it should be noted that there is a mode II component arising from bending of the film at the edge of the delamination the phase angle is = —45 . This highlights the need for mixed-mode interface toughness measurements for material systems relevant to microfluidic systems. 

The experimental set up used for PIV measurements in the glass microchannel with internal diameter of 0.2 mm is depicted in Fig. 3.7. Velocimetry measurements were carried out in the T-junction, in the straight channel, as well as in the bend, as shown in Fig. 3.7c. The channel was etched in a quartz chip, which was sealed through thermal bonding (Dolomite microfluidics). 

In microfluidics the flow is normally laminar but non-laminar flow can occur in components with short channels or orifices, at Reynolds numbers as low as 15 [1]. In our experiments the Reynolds numbers were all below 150 and we observed non-laminar flow conditions where secondary flow and presumable local turbulence was generated at sharp comers in the zigzags of the mini-channel. The maximum Reynolds numbers of the mixing experiments are plotted as a function of the ratio of the length between bends to the hydraulic diameter (L/Dj ) in figure... 

H. Ko, S. Peleshanko, and V. V Tsukruk, Combing and bending of carbon nanotube arrays with confined microfluidic flow on patterned surfaces, J. Phys. Chem. B, 108,4385-4393 (2004). 

This relationship is valid for fully developed flow in a straight channel and does not include the contributions from inlet and outlet feed tubes and minor losses due to ports, bends, expansions/contractions, steps, comers, etc. In most microfluidic fuel cell designs, however, relatively long thin channels are applied where friction losses of the type described by Eq. (2.6) are known to dominate. 

Wilson SA, Jourdain RPJ, Zhang Q et al (2007) New materials for micro-scale sensors and actuators an engineering review. Mater Sci Eng R Rep 56 1-129 Wu Y, Zhou D, Spinks GM, Irmis PC, Megill WM, Wallace GG (2005) TITAN a conducting polymer based microfluidic pump. Smart Mater Struct 14 1511-1516 Wu Y, Alici G, Spinks GM, Wallace GG (2006) Fast trilayer polypyrrole bending actuators for high speed applications. Synth Met 156 1017-1022... 

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