Measurement and simulation of mass transfer and backmixing behavior in a gas-liquid helically coiled tubular reactor

- Different measurement techniques were used to study the gas-liquid mass transfer.
- Computational Fluid Dynamics (CFD) was used to model the gas-liquid mass transfer.
- The results indicate an influence of the coil curvature ratio on the mass transfer.

Volumetric mass transfer coefficients (kLa) and Bodenstein numbers (Bo) for the elongated bubble flow regime in horizontal helically-coiled tube reactors are reported using two different measurement techniques (oxygen optodes, and optical observation of an oxygen-sensitive dye). Additionally, the gas-liquid mass transfer and the residence time behavior of the two-phase flow were described with a 3D Computational Fluid Dynamics (CFD) model, and also with a one-dimensional two-phase model. For this study, 16 cases involving different gas and liquid volumetric flow rates were employed to generate air-water flows through two helically coiled tubes with curvature ratios of δ1=0.093 and δ2=0.3, respectively. The superficial gas and liquid Reynolds numbers (Res,G and Res,L) and the gas hold-up (∊G) are varied from 494 to 2483, from 1456 to 2713, and from 0.46 to 0.81, respectively. The mass transfer measurements show an increasing gas-liquid mass transfer rate with increasing superficial velocity of the liquid-phase and Res,G. The Bodenstein number decreases with increasing gas-phase Reynolds number and increases with increasing superficial velocity of the liquid-phase. Correlations describing the mass transfer and backmixing behavior are proposed. The CFD results are in excellent agreement with the experimental data. With the 1D two-phase model it is possible to describe the residence time behavior of the two-phase flow through the helically coiled tube.