Layer-by-layer carbon nanotube coatings for enhanced pool boiling heat transfer on metal surfaces

Micro/nanotextured coatings have enabled the manipulation of thermal characteristics in pool boiling heat transfer such as the heat transfer coefficient (HTC) and critical heat flux (CHF) because of the ability to optimize bubble formations and departures. However, fabricating such coatings on substrates involves high cost-bulky setup, and is limited by the materials and adhesion properties. Herein, we report layer-by-layer (LbL)-assembled polyethylenimine (PEI)-multi-walled carbon nanotube (MWCNTs) coatings on stainless steel (SS316) to enhance HTC and CHF in pool boiling heat transfer. LbL-assembled PEI-MWCNTs coatings (10, 20, 40 bi-layers) on SS316 were fabricated, whereas bare SS316 substrate and vacuum-filtered MWCNTs coating were prepared as controls. Because of the nano-cavities and the inner-nanoporous structures, LbL coatings showed significant enhancement of HTCs and CHFs compared to bare SS316. Furthermore, denser networks of MWCNTs due to electrostatic bonding and hydrophilic nature of PEI in the LbL coatings could enhance the HTCs and CHFs compared to vacuum-filtered MWCNTs coating. LbL-assembled PEI-MWCNTs of 20 bi-layers showed the highest improvement in HTC, whereas the 40 bi-layers coatings achieved the best enhancement ratio of CHF, (∼147%). Further development of the LbL-assembled coatings on metal surfaces would enable potential applications for thermal management, from micro/nanoscale platforms to macroscale systems.