An investigation of mixing in micro coiled flow inverter in varying tube diameter with fixed reynolds number

Abstract

Micro-scaled Coiled Flow Inverter (MCFI) is a scaled down version of a Coiled Flow Inverter (CFI) which utilizes the principle of flow inversion for process intensification. MCFI is constructed with tubing less than 1.0mm. The microfluidic nature of MCFI caused by low Reynolds number (Re) laminar flow posed as a challenge to achieve effective mixing. Simulation was implemented with Computational Fluid Dynamics (CFD) software FLUENT to visualize the mixing of MCFI with different diameters. Fluid flow of the mixing of two water bodies was simulated. Geometry of the MCFI was designed with tubing diameters of 1.0mm, 0.8mm, 0.6mm and 0.5mm to investigate the effect of cross-sectional diameter towards mixing efficiency. The curvature ratio (λ) was fixed at 10 to reduce the complexity of the system. Fluid flow rate was calculated and adjusted to obtain Re 250 for each tubing size. Velocity profile of tubing within the range of diameter investigated showed negligible difference. Simulation results showed a parabolic velocity profile for straight tube, while skewed velocity profiles were observed within the straight coil and MCFI. MCFI with the tubing diameter of 0.5 mm achieved complete mixing at normalized tube length of 0.69, equivalent to 175mm. MCFI with ID 1.0 mm showed 54.5% mixing, while MCFI with ID 0.8 mm and 0.6 mm showed 69.6% and 78.9% mixing respectively at the outlet. Similarly, fluid in straight tube and straight coil had also failed to achieve complete mixing. Results obtained suggested smaller tubing diameter indeed led to better mixing process in MCFI, in expense of an increase in pressure.