Enhancement of condensation heat transfer by hydrophobic and nano porous surface

It has been well known that surface characteristics such as wettability, morphology, roughness influence on condensation heat transfer on the surface. Especially, hydrophobic and nano porous surfaces enhance condensation heat transfer performance to promote dropwise condensation. Few studies, however, have examined the effects of combined surface with hydrophobic and nano porous to the condensation heat transfer. In order to determine the combined surface effect, condensation heat transfer experiment using hydrophobic and nano porous surfaced was conducted. The nano porous surface was made using Layer-by-Layer (LbL) technique which uses electrically charged particle solutions. Whereas in the case of hydrophobic surface, Self-assembled monolayer (SAM) has been a good approach to control the surface wettability. The surface structure is left unchanged in the deposition of SAM because the particle size is almost small (~3nm), so it is great to make combined surface; nano porous and hydrophobic. In this study, the LbL assembled carbon nanotube (CNT) layers were fabricated to make nano porous surface. On the other hand, the hydrophobic coating is used as octadecyltrichlorosilane (OTS) which has hydrophobic functional group (-CH3). The condensation heat transfer experiment was carried out with four surfaces; bare, CNT, OTS, CNT+OTS. The experimental results indicated that the OTS surface has highest condensation heat transfer coefficient, and CNT+OTS, CNT in order and the bare is lowest.