Nucleate pool boiling heat transfer enhancement in saturated Novec 7100 using titanium dioxide nanotube arrays

The effect of titanium dioxide (TiO2) nanotubes on pool boiling heat transfer is experimentally investigated. Four surfaces including plain or nanotube coated copper or titanium substrates are tested in the saturated Novec 7100. Both the nanotube coated surfaces enhances the critical heat flux (CHF) at around 40% compared to the relative plain surfaces. The nanotube coated titanium substrate effectively improves the heat transfer coefficient at around 65% over the plain surface, while the nanotube coated copper substrate shows the average heat transfer coefficient at about 20% lower than its plain surface. From the coincident boiling curves after reducing a thermal interface resistance from the nanotube coated copper substrate and bubble departure characteristics of the two coated surfaces, it is inferred that the nanotubes are effective in enhancing both the heat transfer coefficient and CHF. The observation shows both the improvements of the nanotube surfaces could be attributed to the modified bubble dynamics and effective rewetting of the dry spots, related to the faster liquid replenishment due to capillary wicking of the tube-like structure. The identification of the TiO2 nanotube influence on pool boiling with the dielectric fluids can help the further applications of the nanotube coating in two-phase cooling systems.