A numerical study of wave characteristics in axisymmetric gas-liquid annular flow in microchannels

Abstract

Microreactors have emerged as a viable option to perform mass transfer limited gas-liquid reactions due to the advantage of high gas-liquid interfacial area density. Slug and annular flow regimes are the two most commonly preferred flow regimes to perform reactions in microreactors. In the annular flow regime, characterized by a continuous gas core and an annular liquid film on the wall, waves are observed at the interface between the two phases. The characteristics of these waves depend on the properties of the fluids and their flow rates. In this work, the hydrodynamics of axisymmetric gas-liquid annular flow in millimeter-size channels is investigated computationally employing volume of fluid method in OpenFOAM solver. CFD simulations have been performed for nitrogen-water and nitrogen-water and ethylene glycol mixture over a range of gas and liquid flow rates. Depending on the gas and liquid flow rates and liquid viscosity, coalescing and non-coalescing waves are observed at the interface. The properties of the interfacial waves such as frequency, wave spacing and wave velocity are determined using spatiotemporal analysis and the effect of gas and liquid flow rates on the wave characteristics is investigated. Further, the time-averaged pressure gradient and interfacial shear stress are reported.