An experimental study on CHF enhancement in flow boiling using Al2O3 nano-fluid

The critical heat flux (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 ～70% in flow boiling for all experimental conditions. Maximum CHF enhancement (70.24%) was shown at 0.01 vol% concentration, 50 °C inlet subcooling, and a mass flux of 100 kg/m² 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.