Since micro channel flow was developed, single phase Microchannel flow has been notorious for chemical reaction because of its low Re. Mixing in micro channel network utilizing chaos theory has shown that the potential but optimum mixing efficiency only can be achieved when Re~ 70, while usually microfluidic flow has Re~ 10. The most important advantages of liquid-liquid slug flow operation in micro channel are the absolute control volume and well mixing behaviour. Preliminary result shows that the synnge pump operating with a synnge above total nominal flowrate of 1 OO~lJhr, giving infusion accuracy of ~ 1.5%. When operating with two syringes simultaneously, average deviation of flow fraction is ~5%. From qualitative analysis from experimental images, disperse phase slug break up at T-junction is driven by a combination of hydrodynamic force and capillary force as well as shear force. Hydrodynamic force is developed from Hagen Poiseulle equation while capillary force is developed from Young-Laplace equation. During slug formation, magnitudes of shear forces were exerted on the interface by the continuous phase because of varying volume in the T-junction available for the continuous phase flow. However, shear force generated just before break up is the most important force. For designing purpose, if the clean snap off of slug break up at the T-junction is desired, narrower micro channel is required. At low Weeff, the disperse phase slug break up occurs at the T-junction with a clean snap off, dominated by a combination of continuous phase upstream pressure and capillary force. At intermediate Weeff, the slug was broken from a disperse phase connecting neck, driven by both combination of forces and shear force. A disperse phase laminar flow region was formed in the micro channel at high Weeffi in which slug break up from the front of the laminar flow region. The break up is dominated by shear force applied by the continuous phase flow on the laminar flow region. A dimensionless number, Rj, which is the ratio of shear force to the combination of hydrodynamic force and capillary force is used for characterizing the importance of forces during slug break up. For Acetonitrile/tetradecane system, slug break up from the front of the disperse phase laminar flow region when Rj> 3.5e-6. The role of shear force in break up becoming more important as Weeff increases, this is because of increasing contact area available for shear. However, estimation of area available for shear from 2D experimental images is difficult. Empirical equations were developed in relating the disperse phase slug length to the frequency of slug formation, in which the threshold slug length is equivalent to disperse phase channel width. The properties of the immisible liquid-liquid systems are more important in characterizing slug break up operation in the micro channel network. Both Weeff and Caeff can be used to characterize the slug length, depends on the region in which researchers interested in.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:505427 |
| Date | January 2007 |
| Creators | Chin, Jitkai |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0019 seconds