Flow behaviour analysis through a venturi designed for industrial and environmental processes

Abstract

The immense environmental challenges facing the world today and in the years to come can be met only through mobilizing the best engineers and scientists in the environmental sector and using innovative and cost-effective solutions. Hydraulic structures can significantly improve dissolved oxygen levels by creating turbulent conditions in which small air bubbles are caused in most of the flow. Therefore, a venturi device can be used as highly effective aerator in aeration processes. However, the hydraulic equipment can be exposed to anomalies due to pressure variations. This is generally caused by the air phase development. Moreover, it considerably induces wall materials, erosion and corrosion. In this work, particular attention was paid to the pressure change in closed venturi pipes because its decrease generates air bubbles and its increase implies their implosion. Both mathematical and experimental tools were used to describe the pressure evolution with flow rates and air bubbles size. Experimental tests were carried out using a transparent rectangular venturi. Pressure field and air section length were measured for different coming flow rates of water. On the other hand, the Rayleigh Plesset ordinary differential equation was used to explain this phenomenon under spherical bubbles hypothesis. High values of the Reynolds dimensionless numbers, at both the upstream and throat sections, indicate a fully turbulent flow through the venturi. Inception was visualized when the air phase starts, before the pressure attains the vapour value. The mathematical model solution shows three flow zones for the pressure field evolution with the relationship between air bubble radius and liquid phase size. So, an unstable flow, inception and a stable cavitating flow were highlighted. Also, the experimental results allow distinguishing these zones depending on the flow rate values. The flow parameters, Reynolds and Thomas dimensionless numbers influence simultaneously the air phase extent. Thus, the present study connects the Rayleigh Plesset equation to turbulence and cavitation flow parameters. This allowed a new flow analysis through a venturi considered by its air phase development.