Amelioration of the pool boiling heat transfer performance via self-assembling of 3D porous graphene/carbon nanotube hybrid film over the heating surface

This study investigates the boiling heat transfer enhancement of 3D porous graphene/carbon nanotube hybrid surface formed via self-assembling. Experimentally, colloidal suspensions of functionalized carbon nanotubes and graphene oxide (at 1:10 wt ratio) and only graphene oxide in water are prepared via sonication using three weight concentrations; 0.00005%, 0.0005%, and 0.005%. Boiling tests are conducted for each prepared fluid using a custom-made boiling apparatus. After boiling tests, Scanning Electron Microscopy analysis is carried out over the heating surfaces in order to observe the deposition behavior of the suspended nanoparticles. For wettability analysis, the contact angle of sessile water droplets on the heating surfaces are measured using the goniometry method. The boiling performance of the heating surface formed by self-assembling of graphene oxide/functionalized carbon nanotube outperforms the self-assembled graphene oxide-only surface with greater critical heat flux and heat transfer coefficient values at all the tested concentrations. A decent interfacial contact of graphene sheets and carbon nanotubes improves surface capillarity and thermal activity. The highly porous surface improves the nucleation site density, bubble departure diameter, and frequency of departure. All these factors contribute enhancement of heat transfer coefficient and critical heat flux.