Two-Phase Flow and Mass Transfer in Helical Capillary Flow Reactors With Alternating Bends

Microstructured devices have gained much attention in R&D and industry as they offer large specific surface area with enhanced mass and heat transfer. Helically coiled tubular devices in micro-scale can further increase the performance in terms of transport phenomena, as secondary flow (Dean vortices) enhances the radial mixing along the tube. In the content of this work liquid-liquid mass transfer of different helical capillary flow reactors was investigated and compared with straight capillaries by using water/acetone/butyl acetate test systems for liquid extraction. Helically flow capillary reactors with alternating bends and straight capillaries were fabricated by using FEP tubes (fluorinated ethylene propylene) with inner diameter of 1 mm. Slug flow was introduced within the reactors by utilizing T-shaped mixing elements at the inlet. In order to obtain robust and precise downstream analyses, a continuously working, in-line phase splitter was fabricated and connected to the outlets of the reactors. It instantaneously splits the organic and aqueous phases depending on their wettability characteristics. Total volumetric flow rate was varied in the range of 1–8 mL min⁻¹ and volumetric flow ratios (aq/org) in the range of 0.5–2.0. Effects of contact time, volumetric flow ratio, and the reactor geometry on extraction efficiency were investigated for the experiments at ambient temperature by generating slug flow patterns. Experimental results revealed that the helical capillary flow reactors offer higher extraction efficiency up to 20 % compared to straight capillaries at constant contact times. Hence, these types of reactors can be applied for liquid-liquid mass transfer processes, which require longer residence time due to slow mass transfer rates.