The critical heat NIX (CHF) is one of the most Important thermal hydraulic parameters in heat transfer system design and safety analyses. CHF enhancement allows higher limits of operation conditions such that heat transfer equipment can be operated safely with greater margins and better economy. The application of nano-fluids IS thought to have strong potential for enhancing the CHF. In this study, zeta potentials of Al2O3 nano-fluids were measured and flow boiling CHF enhancement experiments using Al2O3 nano-fluids were conducted under atmospheric pressure. The CHFs of Al2O3 nano-fluids were enhanced up to similar to 70% in now boiling for all experimental conditions. Maximum CHF enhancement (70 24%) was shown at 0 01 vol% concentration, 50 degrees C inlet subcooling, and a mass flux of 100 kg/m(2) s. Inner surfaces of the test section tube were observed by FE-SEM and the zeta potentials of Al2O3 nano-fluids were measured before and after the CHF experiments (C) 2009 Elsevier Ltd All rights reserved.