Experimental and numerical evaluation of slugs in a vertical air–water flow. (April 2018)

• Record Type: Journal Article
• Authors: Jaeger, J.; Santos, C.M.; Rosa, L.M.; Meier, H.F.; Noriler, D.
• Is Part Of: International journal of multiphase flow. Volume 101(2018)
• Page Start: 152
• Page End: 166
• Publication Date: 2018-04
• Subjects: Slug flow regime -- Air–water flow -- Computational fluid dynamics -- Volume of Fluid -- Discretization schemes; Multiphase flow -- Periodicals; Écoulement polyphasique -- Périodiques; Multiphase flow; Periodicals; 620.1064
• DOI: 10.1016/j.ijmultiphaseflow.2018.01.009
• Languages: English
• ISSNs: 0301-9322

Abstract

Highlights: Vertical slug flow in a large diameter duct was experimentally and numerically studied. PDF analysis of pressure and gas holdup was done. Good agreement was observed when comparing the PDF moments values. There was an expansion of the gas phase toward the top of the duct. Higher liquid flow rate can speed up or slow down the flow, depending on the gas amount. Graphical abstract: Abstract: Multiphase flows are often present in chemical processes and they include gas-liquid transport, which may become intermittent depending on the operating conditions. One type of flow structure is the presence of large gas bubbles that can occupy the entire duct diameter, separated by liquid portions. This can result in large pressure fluctuations, which are normally associated with damage to equipment over time. The intermittent nature and the chaotic distribution of the phases in a turbulent flow complicate the design and optimization of the equipment. In this context, computational fluid dynamics is a useful technique since it can provide important information on several flow conditions, but the use of suitable models and boundary conditions is required. In this study, an air and water flow with the presence of slugs is evaluated in a system consisting of horizontal and vertical ducts, with an inner diameter of 94 mm. Experimental data on the pressure and void fraction were analyzed and compared to the predictions obtained from numerical simulations, obtained considering the VOF approach. It was observed that the use of the geometrical reconstruction scheme to simulate a compressible flow resulted in a better agreement with the experimental results. Using this setup, the average volume fraction and pressure values showed the expected behavior. The frequency of slugs, established using three different methods, was around 1.5 Hz for the evaluated conditions evaluated. The pressure probability density function (PDF) indicated good agreement between numerical simulations and experimental data, while the volume fraction PDF indicated that the flows evaluated have the characteristics of a churn flow regime. Moreover, it was found that an increase in the water flow rate can lead an increase or a decrease in the average velocity.