ISSN On-line: 2688-7231
ISBN On-line: 978-1-56700-524-0
Proceedings of the 26thNational and 4th International ISHMT-ASTFE Heat and Mass Transfer Conference December 17-20, 2021, IIT Madras, Chennai-600036, Tamil Nadu, India
Experimental Analysis of the Post Dryout Flow Regimes Encountered during Rewetting by Bottom Flooding using High Speed Chrono-photography
When a highly superheated tube is flooded with coolant, the excess superheat generates copious amount of vapor. This vapor layer repels the liquid to form a central core while the vapor occupies an annular region of the tube. However, as heat transfer increases with the propagation of the coolant front, the vapor layer collapses and the solid-liquid contact is re-established − a phenomenon described as rewetting. The film boiling regime encountered during rewetting phenomenon is categorized into the inverted annular flow (a liquid core is surrounded by vapor annulus), agitated flow (liquid core breaks up into agitated region of slugs or large liquid droplets) and dispersed flow (small liquid droplets levitated in the vapor column). The present study focusses on the experimental analysis to obtain a direct quantification of the film boiling regime observed during rewetting phenomenon. An image processing technique is adopted for this purpose where the two-phase flow regimes are characterized based on the pixel level information from a sequence of images. The chronophotographic sequence over a fixed area of interest can bear the signature of different typical flow regimes. Rigorous image processing is carried out to analyze the captured high speed sequences and investigate the effect of different parameters on the inverted annular flow and dispersed flow.