This study describes flow boiling critical heat flux (CHF) experiments using Al2O3 nanofluid and Al2O3 nanoparticle deposited tubes. The flow boiling CHF of Al2O3 nanofluid with a plain tube (NFPT) and de-ionized water with an Al2O3 nanoparticle deposited tube (DWNT) were enhanced up to about 80% for all experimental conditions. There was no big difference in the CHF results between NFPT and DWNT: these results indicate that the CHF enhancement of Al2O3 nanofluid is surely caused by deposition of nanoparticles on the test section tube inner surface. After the flow boiling CHF experiments, the inner surfaces of the test section tube were explored by FE-SEM, which revealed the deposition of Al2O3 nanoparticles on the heated surfaces. (C) 2010 Elsevier Ltd. All rights reserved.