Abstract
A quantitative analysis of two imaging modalities, shadowgraphy and x-ray imaging, is presented in the framework of void fraction determination. The need for this arises from the fact that shadowgraphs are sometimes utilized to quantify void fraction profiles, which is an unproven method. Time-averaged x-ray images are used to evaluate the performance of the time-averaged shadowgraphs. The case of a cavitating flow through an axisymmetric converging-diverging nozzle (‘venturi’) is considered, for three separate cavitation numbers. The complex nature of the cavitating flow through the venturi manifests itself in the occurrence of three distinct regimes: a swarm of tiny bubbles; a large, coalesced cavity near the wall; and a drifting/collapsing cavity. The flow regime governs the performance of shadowgraphy for void fraction determination, with two of the three regimes deemed acceptable for shadowgraphy. The quantitative comparison exemplifies that sole reliance on shadowgraphy may lead one to draw improper conclusions on the void fraction distributions, even at a qualitative level.
Highlights
There are many industrial applications involving multiphase flows, including sprays, fluidized beds, bubbly flows and cavitating flows
The flow regime governs the performance of shadowgraphy for void fraction determination, with two of the three regimes deemed acceptable for shadowgraphy
Three different cavitation numbers are considered for comparison in the current study: 0.60, 0.72 and 0.88, whose results are illustrated in figures 7–9 respectively
Summary
There are many industrial applications involving multiphase flows, including sprays, fluidized beds, bubbly flows and cavitating flows. A common characteristic of these flows is that they are often optically opaque This is due to multiple scattering of visible light by particles/bubbles in its path. Owing to the lack of penetrability of visible light in such optically opaque flows, alternative techniques have been developed to quantitatively characterize the phenomena occurring in the interior of the flow [1, 2]. Of the multiphase flows introduced earlier, cavitating flows are slightly different, as a predetermined global void fraction of a certain phase cannot be introduced into the flow. This is due to the phenomenon of cavitation, where liquid vaporizes upon reaching a pressure below its vapor pressure. Void fraction is a major quantity of interest in cavitating flows as it can be used to demarcate the distinct shedding mechanisms [5, 6]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
