Vertical-length effect on dropwise condensation heat transfer at low heat flux - Part I: Experimental study

Due to its superior heat transfer performance, dropwise condensation has been studied for industrial applications. This paper experimentally reports the effects of vertical length on dropwise condnsation in the presence of noncondensable gas. The formation of rivulet flows, which reduce heat transfer due to droplet coalescence, was observed. Compared to the upper side, rivulet flows on the lower side of the condensing surface were faster and more frequent. Lower heat flux was also measured on the lower side, indicating a correlation between heat transfer and rivulet flow parameters during dropwise condensation on the vertical surface. These findings represent the first study of the effects of rivulet flows on dropwise condensation heat transfer, and they can be applied to evaluate condensation heat transfer on long vertical surfaces, such as those found in small modular reactor containment systems as well as large containment building with passive containment cooling systems.