Abstract
An X-ray microtomography (µCT) system was adapted so that 3D scans of fixed horizontal or vertical test sections can be performed. The mobile µCT system has been applied to measure the local, time-averaged volume fraction distribution of developing annular air-water flow in a horizontal pipe with µm spatial resolution. Based on the volume fraction data the liquid film thickness profile is computed and the accumulation, stripping and renewal of the annular liquid film at a circular orifice is studied. The development length of the annular flow downstream of the orifice is evaluated based on the integral volume fraction and the change of the film thickness profile along the pipe axis. Both parameters give a consistent result, indicating that liquid film renewal can be judged based on integral measurement techniques in this case. Further, the detailed 3D data enables the validation of computational fluid dynamics codes based on phase-averaged variables such as the Euler-Euler approach.Graphic abstract
Highlights
Horizontal two-phase flows occur in a variety of industrial applications, e.g. pipeline transportation of oil and gas, apparatuses in the chemical industry, direct steam generation solar power plants and heat exchangers
This work tries to bridge this gap by applying tomographic measurement techniques to obtain volume fraction and film thickness distribution in horizontal annular flow through a circular orifice, which is frequently encountered in process equipment at high mass flux conditions
The uncertainty analysis of the computed tomography (CT) system showed that reconstruction artifacts caused by repositioning of the test section in the inhomogeneous X-ray cone beam are the dominating sources of error with an estimated maximum error magnitude of ±5% liquid volume fraction
Summary
Horizontal two-phase flows occur in a variety of industrial applications, e.g. pipeline transportation of oil and gas, apparatuses in the chemical industry, direct steam generation solar power plants and heat exchangers. The heat and mass transfer in such processes is closely related to the spatial gas and liquid phase distribution. Consider for example the steam condensation or flow boiling in pipes where the wall heat flux decreases when a closed liquid or gas film is formed, respectively. For the design of such industrial-scale process equipment, flow simulation methods based on phase-averaged variables—such as the two-fluid model—are increasingly popular as they promise three-dimensional flow information at relatively low computational cost. While these methods are often well validated against analytical or academic test cases, validation data for two-phase flow in non-trivial geometries is rarely available. This work tries to bridge this gap by applying tomographic measurement techniques to obtain volume fraction and film thickness distribution in horizontal annular flow through a circular orifice, which is frequently encountered in process equipment at high mass flux conditions
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