Abstract
While the number of computational studies considering two-phase flows in microfluidic systems with or without mass transfer is increasing, numerical studies incorporating chemical reactions are still rare. This study aims to simulate the catalytic hydrogenation of nitrobenzene in gas-liquid Taylor flow by combining interface-resolving numerical simulations of two-phase flow and mass transfer by a volume-of-fluid method with detailed modeling of the heterogeneous chemical reaction by software package DETCHEMTM. Practically relevant physical properties are utilized for hydrodynamic and mass transfer simulations in combination with a preliminary reaction mechanism based on density functional theory. Simulations of mass transfer are conducted using a predetermined velocity field and Taylor bubble shape. At the beginning of the simulation when liquid nitrobenzene is not saturated by hydrogen, axial profiles of surface species concentrations and reaction rates show local variations. As hydrogen dissolves in nitrobenzene, the concentration profiles of surface species at the wall become uniform, eventually reaching an equilibrium state. Neglecting the local variation in a short initial period will allow further simplification of modeling surface reactions within a Taylor flow.
Highlights
Microfluidic systems operating with continuous multiphase flows have emerged as an attractive technology characterized by fast heat transfer, efficient mixing, short residence time and an absence of hydrodynamic dispersion [1]
The present study aims at a qualitative feasibility study of employing a detailed surface reaction mechanism in interface-resolving simulations of a gas-liquid flow. aTodetailed that end, the computer
The present study aims at a qualitative feasibility study ofTaylor employing surface reaction codes TURBIT-VOF
Summary
Microfluidic systems operating with continuous multiphase flows have emerged as an attractive technology characterized by fast heat (and mass) transfer, efficient mixing, short residence time and an absence of hydrodynamic dispersion [1]. The predominant two-phase flow pattern in microchannels at sufficiently low gas and liquid superficial velocities is segmented flow, which consists of a sequence of elongated gas bubbles (Taylor bubbles [2]) separated by liquid slugs. Segmented flow ( known as Taylor flow) significantly improves chemical reaction rates and efficiency [3] and is beneficial for multiphase monolith reactors [4] by means of a very thin liquid film between bubbles and catalytic wall as well as large interfacial area [5]. Taylor flow that governs the reaction efficiency depends on liquid phase diffusion coefficient [6], linear velocity [7], gas superficial velocity [8] or channel size [9]. Recent reviews provide detailed insight on the subject [10,11,12].
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