Investigation of liquid phase axial dispersion in Taylor bubble flow by radiotracer residence time distribution analysis

A gas-liquid Taylor bubble flow occurs in small diameter channels in which gas bubbles are separated by slugs of pure liquid. This type of flow regime is well suited for solid catalyzed gas-liquid reactors in which the reaction efficiency is a strong function of axial dispersion in the regions of pure liquid. This paper presents an experimental study of liquid phase axial dispersion in a Taylor bubble flow developed in a horizontal tube using high speed photography and radiotracer residence time distribution (RTD) analysis. A parametric dependence of axial dispersion on average volume fraction of gas phase was also investigated by varying the relative volumetric flow rates of the two phases. Ba-137m produced from a Cs-137/Ba-137m radionuclide generator was used as radiotracer and measurements were made using the NaI(T1) scintillation detectors. Validation of Ba-137m in the form of barium chloride as aqueous phase radiotracer was also carried out. Axial Dispersion Model (ADM) was used to simulate the hydrodynamics of the system and the results of the experiment are presented. It was observed that the system is characterized by very high values of Peclet Number (Pe similar to 10(2)) which reveals an approaching plug type flow. The experimental and model estimated values of mean residence times were observed in agreement with each other.