Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.
Re-wetting of a hot dry surface is the establishment of
direct contact between the surface and a liquid at a lower
temperature. Re-wetting heat transfer is characterized by a large
increase in heat transfer from the surface and occurs when a
vapor film existing between the dry surface and the liquid is
destabilized. Study of re-wetting heat transfer is very important
in nuclear reactor safety for limiting the extent of core damage
during the early stages of severe accidents after loss of coolant
accidents LOCA and is essential for predicting the rate at which
the coolant cools an overheated core. Surface re-wetting is
established by the formation of a wet patch on the hot dry
surface which then grows in size to cover the entire surface.
The leading edge of the wet patch is called the re-wetting front
and consists of transition and nucleate boiling heat transfer
regions. The aim of this study is to introduce and study two
important variables related to the re-wetting front as it moves
on hot horizontal tubes cooled by water jet impingement. These
variables are: the rebound phenomenon of the re-wetting front
and the width of the re-wetting front. Experimental
observations of this study showed that the re-wetting front
could rebound a small distance just after the formation of the
wet patch due to rapid heat conduction in the solid towards the
wet patch. The rebound distance was found to increase by
decreasing water temperature and the velocity of the jet. The
width of the re-wetting front was found to increase by
increasing water temperature and decreasing the initial surface
temperature. As the solid thermal conductivity increases, this
width was found to increase.
