A novel geometrically-hybrid microchannel for performance enhancement in mass transfer: Description of Lyapunov exponent and Poincaré map

Abstract

Typical laminar convective mechanisms of fluid mixing in the passive micromixers in literature were investigated separately in terms of fluid inlet pattern, barrier shape and location, flow direction, and making a bypass for fluid streams. In the presently studied micromixers, different geometries, including T-shaped inlet, bent, barrier, and convergence-and-divergence sections are utilized to improve mixing efficiency. These geometries provide the fluid with chaotic mixing at high Re number. The mixing in the micromixers can be analyzed via Poincare map or Lyapunov exponent description. A new calibration method is presented for quantitative mixing characterization using digital image analysis. Moreover, the relative roles of bent and barriers (symmetric and asymmetric) are investigated. It was shown that at high Re numbers, the role of bent and barriers in mixing quality and mixing effectiveness are considerable, and by removing the internal barriers the mixing index decreases only 20% and 30% in symmetric and asymmetric barrier designs, while at low Re numbers, two streams passed from bents side by side without considerable mixing. Moreover, in asymmetric design and at high Re numbers when the streams move transversely to the other sides fluid-driven cavities assumed to be as local mixers.