Flow boiling heat transfer characteristics of nano-refrigerants in a horizontal tube

• The heat transfer coefficient increased with increased nanoparticle mass fraction.
• Cu nanoparticles had the best effect in enhancing the heat transfer performance of the nano-refrigerants.
• With increased quality, the heat transfer coefficient of nano-refrigerants increased.
• With increased mass velocity, the heat transfer coefficient of nano-refrigerant increased.

The flow boiling heat transfer characteristics of four nano-refrigerants with different mass fractions, qualities, and mass velocities in a horizontal tube were studied. The nano-refrigerants were Cu-R141b, Al-R141b, Al2O3-R141b, and CuO-R141b. The nanoparticle mass fractions were 0.1 wt%, 0.2 wt%, and 0.3 wt%; the quality ranged within 0.3–0.8; and the mass velocities were 120, 210, and 330 kg m−2 s−1. Results showed that the flow boiling heat transfer was enhanced by nanoparticle addition. The heat transfer coefficient of the nano-refrigerant increased with increased mass fraction, quality, and mass velocity. The mass fraction of nanoparticles was the main factor that influenced the heat transfer coefficient. The heat transfer enhancement effects of the different nano-refrigerants differed, with the highest enhancement achieved using Cu-R141b. At G = 120 kg m−2 s−1 and 0.3 wt% mass fraction, the maximum heat transfer coefficient of Cu-R141b increased by 49% (average increase = 27%).