The effect of surface area on pool boiling heat transfer coefficient and CHF of Al₂O₃/water nanofluids

In this study, pool-boiling experiments are carried out to find out the influence of nanoparticles on boiling heat transfer coefficient and CHF. Each surface of the heater is visualized with FE-SEM and AFM after the experiments to figure out the effective boiling areas. The CHF increases up to 103% (compared to pure water) as the particle concentration increases until 0.001 vol% while it starts to decrease gradually as the particle concentration increases more than 0.001 vol%. It is found that the increase of CHF is proportional to the effective boiling surface area and the reduction of boiling heat transfer coefficient (BHTC) is mainly attributed to the blocking of the active nucleation cavity and the increase of the heat transfer resistance by nanoparticle deposition on the boiling surface. Finally, this study proposes a novel mechanism for BHTC reduction and CHF enhancement by nanofluids by considering the effective surface area variation.