Mass transfer characteristics of gas–liquid absorption during Taylor flow in mini/microchannel reactors

2011 ◽

Cited By ~ 1

Author(s):

Harish Ganapathy ◽

Ebrahim Al-Hajri ◽

Michael M. Ohadi

Keyword(s):

Mass Transfer ◽

Reaction System ◽

Unit Cell ◽

Phase Field Method ◽

Co2 Absorption ◽

Computational Domain ◽

Microchannel Reactor ◽

Taylor Flow ◽

Transfer Characteristics ◽

Flow Microreactor

The aim of this work is to investigate numerically the mass transfer characteristics in a Taylor flow microchannel reactor. Previous attempts to model gas-liquid mass transfer in microchannels have mainly been done by the unit cell based models. Limitations of this approach are its incapability to account for the mass transfer in the inlet mixing region and the dependence on empirical data to define the unit cell geometry. The present work attempts to overcome both these shortcomings by adopting a purely numerical approach to model the mass transfer in a Taylor flow microreactor. A finite-element implementation of the phase field method was used to predict the hydrodynamics of the two-phase flow The flow pattern obtained was used to define the computational domain to model the mass transfer. The reaction system of CO2 absorption into aqueous NaOH solution was considered for gas superficial velocities ranging from 0.09 to 0.25 m/s with the liquid phase superficial velocities ranging from 0.02 to 0.21 m/s. Channels with hydraulic diameters ranging from 100 μm to 500 μm were considered with flow focusing and cross flow types of inlet configuration. The effect of channel length was also studied by varying the residence time in the transient simulation. Results suggest that the conventional unit cell based approaches which do not model the inlet mixing region could over predict the mass transfer by up to 16%. Smaller diameter channels were found to have improved mass transfer characteristics. This was found to be further enhanced by higher concentration levels of the liquid reactant and higher temperatures. The channel wall wettability was found to negligibly affect the mass transfer characteristics. The predictions from the present model were compared with experimental data as well as with predictions of the unit cell based model and a good agreement was obtained with both models.

Download Full-text

Hydrodynamics of Taylor flow in small channels: A Review

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1243/09544062jmes776 ◽

2008 ◽

Vol 222 (5) ◽

pp. 737-751 ◽

Cited By ~ 122

Author(s):

P Angeli ◽

A Gavriilidis

Keyword(s):

Mass Transfer ◽

Cross Sections ◽

Bubble Velocity ◽

Flow Properties ◽

Hydrodynamic Properties ◽

Taylor Flow ◽

Transfer Characteristics ◽

Flow Circulation ◽

Inlet Conditions ◽

Small Channels

The improved mass transfer characteristics of Taylor flow, make it an attractive flow pattern for carrying out gas—liquid operations in microchannels. Mass transfer characteristics are affected by the hydrodynamic properties of the flow such as thickness of the liquid film that surrounds the bubbles, bubble velocity, bubble and slug lengths, mixing, and flow circulation in the liquid slugs, and pressure drop. Experimental, theoretical, and modelling attempts to predict these properties are reviewed and relevant correlations are given. Most of these refer to capillaries but there are number of studies on square channels. In general, flow properties are well understood and predicted for fully formed Taylor bubbles in a developed flow and in clean systems, particularly in circular channels. However, the presence of impurities and their effect on interfacial tension cannot be fully accounted for. In addition, there is still uncertainty on the size of bubbles and slugs that form under certain operating and inlet conditions, while there is little information for channels with non-circular cross-sections.

Download Full-text