Bifurcation in a T-channel junction: Effects of aspect ratio and shear-thinning

It is well known that, beyond a critical aspect-ratio-dependent Reynolds number, the flow in a three-dimensional T-channel junction, i.e. two-opposing planar channel streams joining and turning through 90°, can break symmetry. This flow bifurcation has been proposed as a method of enhancing mixing in microfluidic channels where significant increases in mixing quality are observed beyond the bifurcation. In the current paper we investigate the critical conditions for the onset of this steady symmetry-breaking phenomenon in terms of both the inlet and outlet channel aspect ratios across a wider parameter range than has been probed hitherto. In so-doing we show that the change in flow conditions from symmetric to asymmetric flow is, in most cases, a steady supercritical pitchfork bifurcation and we confirm that an existing correlation (Soleymani et al., 2008b) for predicting the critical conditions can fail under certain aspect ratio combinations. In addition we find bifurcation occurs for many cases in which a recent study claimed it was absent (Cherlo and Pushpavanam, 2010) and in one of these cases the bifurcation is to an unsteady asymmetric state. Additionally, we investigate the effect of non-Newtonian fluid characteristics on the critical Reynolds number. In particular we use the power-law model to investigate the effect of shear-thinning in the power-law index range 0.5≤n≤1.