Sandro Pintus

Statistical characterization of slug flow in horizontal pipes

Abstract Air/water slug flow in 53 and 90 mm i.d. horizontal pipes has been investigated for a large range of gas and liquid velocities. For this purpose a special instrumentation with simultaneous data acquisition and analysis has been developed. This has been used to determine the mean slug characteristics (length, holdup and velocity) and their statistical distributions.

Time-series analysis approach for the identification of flooding/loading transition in gas–liquid stirred tank reactors

Abstract This work provides a simple method for the objective, quantitative and non-intrusive detection of flooding/loading transition in gas/liquid systems in agitated vessels starting from the time-series analysis of conductance fluctuations along a generic cross section of the vessel. The conductance probe is designed in order to introduce minimal perturbations of the flow field within the vessel. A thorough statistical characterization of the time series collected by the probe provides deeper insight into the fluid dynamics of gas–liquid systems in stirred vessels as well as a simple, objective way to detect flooding/loading transitions.

Macro-Instabilities in Eccentrically Agitated Vessels

Laser Doppler anemometry and flow visualisation are used to shed light into the main turbulent flow features of an unbaffled vessel stirred by an eccentrically positioned Rushton turbine. Two main vortices, one above and one below the impeller, are present and the former vortex dominates the flow field, driving a strong circumferential flow around it. The vortices are not steady but oscillate slowly and periodically inducing a kind of flow instabilities, which may have a significant impact on macro-mixing. The characteristic frequencies of such flow instabilities were found to increase with reducing the impeller blade thickness, thus it is argued that their origin is related to the interaction between the impeller discharged stream and the vessel wall/bottom.