Experimental and Numerical Investigation of Multiphase Flow Characteristics in T-Shaped Microchannels

Abstract

Microfluidics play an essential role in process intensification. These devices facilitate safe environment for reaction, better process control, high heat and mass transfer rates. The performance of these devices depend on the flow behaviour, flow regimes, macro and micromixing. Hence, in this work, the hydrodynamics, macro mixing, single-phase flow regimes, micromixing and crystallization in the T-shaped microchannel are investigated numerically and experimentally. First, the hydrodynamics and macro mixing in the microchannel are predicted using CFD simulations and are validated with experiments. To improve the flow field and macro mixing, rectangular and trapezoidal baffle configurations are introduced in the flow channel. The macro mixing in the microchannel is characterized through Residence Time Distribution (RTD). The extent of axial and lateral mixing are quantified to find an optimum baffle configuration that supports flow field and macro mixing in T-shaped microchannel. As introduction of these baffles in the flow channel induces higher pressure drop, various single phase flow regimes in T-shaped microchannel are identified in terms of flow Reynolds number. In engulfment flow regime, mixing is found to be high and this flow regime occurs when flow Reynolds number is 300. To obtain engulfment flow regime at low Re (75) convergent – divergent inlets are proposed. The extent of macro mixing at different flow regimes are numerically quantified by injecting buoyant tracer particles and computing their trajectories through Lagrangian approach. This is qualitatively analyzed through Poincarè maps and quantified with Shannon’s entropy. The role of micromixing on reaction between 1-naphthol and di-azotized sulphanilic acid is numerically analyzed for different flow regimes. The micromixing performance is found to be low in vortex flow regime and high in engulfment flow regime. The extent of micromixing is found to be superior when convergent – divergent inlets (C:D = 9:1) are introduced. As an application study, antisolvent crystallization of NaCl is considered in the microchannel. The crystal size distribution (CSD) and growth are predicted using Population Balance Model (PBM). The crystal growth and CSD are predicted using discrete method of PBM. The CSD is found to be narrow when flow Reynolds number increases. To improve crystal growth, CSD and crystal yield, various dosing modes are proposed and optimum conditions are ii identified (phase lag = 180o, frequency = 20 Hz, amplitude = 0.05 m/s) for high crystal yield and narrow CSD.