Abstract
Flow characteristics of visco-elastic fluids sweeping a micro-cavity mounted in a micro-duct have been investigated in order to develop a novel technique of a mixing process for micro-reactors. In this paper, effects of the Reynolds number and of the rheological characteristics of the fluids were focused on. The cavity depth, the cavity length and the width of the wider flow path were fixed at 200, 1,000 and 400 u,m, respectively. As a visco-elastic fluid, a solution of cationic surfactants with counter-ions was used. The molar ratio of counter-ions to surfactants was changed in four steps in order to change the rheological characteristics of the visco-elastic fluids. The Reynolds number was also changed from 0.100 to 100. From the results, it was found that a tonguing motion of the separation fluid bubble tip formed in the downstream region in the cavity occurs at a certain Weissenberg number larger than 200 due to the elastic instability. The fluctuating bulge structure was also observed on the upstream side wall of the cavity in a higher range of the Weisenberg number. Such an elastic instability can be expected a suitable micro-fluid motion for the micro-mixing.
