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Experimental study of boiling in porous media: effect of the void fraction on the critical heat flux

Gourbil, Ange and Duru, Paul and Fichot, Florian and Quintard, Michel and Prat, Marc Experimental study of boiling in porous media: effect of the void fraction on the critical heat flux. (2016) In: 9th International Symposium on Heat Transfer ISHT-9, 15 August 2016 - 19 August 2016 (Beijing, China).

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Abstract

Following a loss of coolant accident in a nuclear reactor, the materials of the core can crumble and form a porous, hot debris bed that must be efficiently cooled. This is done by reflooding the debris bed with water. This operation involves complex thermal-hydraulic phenomena that are better understood by studying forced convection boiling in heating porous media. To that end, we use a heat-generating model porous medium made of 392 cylindrical temperature probes transversely placed between two ceramic plates. The probes are used both as temperature sensors and as heating elements. The front ceramic plate is transparent, allowing visualization of the flow inside the test section. Boiling curves are obtained by applying an increasing heating power to one specific element, while a constant global heating power is applied to the other elements. On the one hand, thermal measurements show that the critical heat flux on a specific element decreases as the global thermal power released by the porous medium increases. On the other hand, visualizations show that the void fraction in the test section increases with the global heating power. An image processing program was developed to measure the void fraction and characterize the bubble dynamics, in order to investigate their influence on the critical heat flux. Such measurements have been validated using a second test section where air is injected at a known flow rate inside the device, at isothermal conditions, and where flow regimes comparable to those observed in the boiling experiment are obtained. In this talk, we will present the experimental techniques allowing to measure the void fraction in our experiment, before discussing the influence of this parameter on the critical heat flux.

Item Type:Conference or Workshop Item (Speech)
Additional Information:Thanks to the American Society of Mechanical Engineers(ASME). This paper appears in : Proceedings of the 9th International Symposium on Heat Transfer - ISHT9. The definitive version is available at http://asmedigitalcollection.asme.org
HAL Id:hal-01375366
Audience (conference):International conference proceedings
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
French research institutions > Institut de Radioprotection et de Sûreté Nucléaire - IRSN (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
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Deposited On:03 Oct 2016 07:27

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