(129a) Pressure Drop in the Micro T-Junctions

Over the past decade, computational methods have proven to be an effective tool to design and develop microprocesses1). This opens up the possibility of ensuring the feasibility of processes in microreaction devices or to optimize these devices on a computer with a minimum expenditure of the time and money.

Fig. 1. Schematic picture of the T-mixer with dimensions A× B×C

In this study results are presented from a numerical study examining the pressure drop of the liquid phase inside micro T-junctions (Figure 1) at moderate Reynolds numbers where the flow is either in the vortex or in the engulfment flow regimes2). Figure 2 presents the crosssectional pressure along the mixing channel for a 600 × 300 × 300 mixer at Re = 80 , and Re = 240 . The values of the pressure are sharply decreased at the mixing zone due to deflection of the inflowing streams. However after the mixing zone, a linear pressure dependence is observed as expected for the fully developed duct flow. The main aim was to propose an explicit equation to predict the pressure drop inside T-junctions. To end this, the effects of variation in operating and design parameters, such as the volume flow rate, the aspect ratio of the mixing channel or the hydraulic diameters of the channels on the pressure drop were studied.

Fig. 2. Cross-sectional pressure along the mixing channel for a 600× 300 × 300mixer at (a) Re = 80 , and (b) Re = 240.

In a T-type micromixer the mixing of liquids occurs in the region where convection is the main mixing process owing to the fact that the diffusion constant is very small in the orders of 10-9 m2/s. As depicted in Figure 3 convection in the mixing zone is a result of the deflections of the inflowing streams. In the design of a micro T-mixer it is essential to ensure that the mixing channel is longer than the mixing zone to have the efficient mixing. In this study, a model was proposed for determination of the mixing zone in terms of the different operating and design parameters.

Fig. 3. Streamlines at the entrance of the mixing channel. Colour is used to distinguish between the streams entering each of the inlet channels. The swirling of the fluid flow results in dragging fluids from the middle to the top and bottom sides of the mixer.

A set of experiments was carried out to support the simulation results. The model results

were found to be consistent with experimental findings.

References

1.          Mengeaud V., Josserand J., and Girault H. H., Mixing Processes in a Zigzag Microchannel: Finite Element Simulations and Optical Study, Anal. Chem., 74, 4279 (2002).

2.          Soleymani A., Kolehmainen E., and Turunen I., Numerical and experimental investigations of liquid mixing in T-Type micromixers, Chem. Eng. J., 135S1, S219 (2007). H, Weinheim (2000).