Experimental study of the dryout of a 2D heat-generating model porous medium
Résumé
Dryout experiments are performed in a quasi two-dimensional heat-generating model porous medium, with
bottom flooding. The test section is composed of an array of heating cylinders placed between two ceramic
plates. It is held vertically and a liquid (HFE-7000) is injected from bottom at a controlled flow rate, pressure and
temperature. Dryout incipient power is investigated by applying an increasing thermal power to a bundle of
heating cylinders until a dry zone is detected. The liquid inlet mass fluxes range from 1.0 kg m 2 s 1 to
10.5 kg m 2 s 1 and the heat fluxes are between 195 kW m 2 and 1086 kW m 2. Two kinds of dryout phenomenology
are observed. First, at low liquid injection rate (below 4.2 kg m 2 s 1 inlet mass flux), reaching the
dryout power results into a liquid front receding from the top of the test section to the upper limit of the heated
zone, while downstream the heated zone, the porous medium is vapour-saturated. Second, at higher flow rate
(over 5.2 kg m 2 s 1 inlet mass flux), the boiling crisis happens at the surface of a single heating element, resulting
in a local film boiling, whereas a two-phase flow still go through the whole test section. In both cases,
high-speed visualizations allow characterizing 8 boiling/flow regimes, depending on the inlet mass flux, the
power released by the heated zone, and the location inside the porous medium. In particular, when reaching the
dryout incipient power, the existence of a pulsed flow regime is highlighted. Such a characterization of boiling/
flow regimes might be helpful in improving dryout models.
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