Enhancement of critical heat flux using nano-fluids for Invessel Retention–External Vessel Cooling

This study investigated the pool boiling critical heat flux (CHF) of water-based nano-fluids under atmospheric pressure for Invessel Retention (IR)–External Vessel Cooling (EVC). The heated surface was a stainless steel foil inclined at different orientation angle from 0° (horizontal downward facing position) to 90° (vertical position). Three working nano-fluids with high suspension stability were selected by the zeta potential method to investigate the effect of each nano-fluid on CHF at the heated surface, which were 0.05% Alumine (Al2O3), 0.05% carbon nanotubes (CNT) + 10% boric acid and 0.05% Al2O3 + 0.05% CNT. It was observed that these nano-fluids enhanced CHF significantly (up to 220%) compared to deionized (DI) water. Furthermore, for all test fluids, CHF increased when the orientation angle increased. The surface characterization after boiling tests shows that the CHF enhancement with nano-fluids can be related to the increase of both surface roughness and wettability caused by nanoparticle deposition during the boiling processes.