A test rig with a horizontal smooth tube was built to measure flow boiling heat transfer of nanolubricant/refrigerant. The experimental study on heat transfer characteristics of graphite-nanorefrigerant flow boiling inside a horizontal smooth copper tube

with total length of 2.5 m

outside diameter of 9.52 mm

inside diameter of 8 mm and wall thickness of 0.76 mm was performed. Influence of graphite on flow boiling heat transfer characteristics of nanorefrigerant/oil mixture was investigated. There were three kinds of fluid under experiment:R600a

R600a/oil and graphite nanorefrigerant/oil with different graphite mass fractions (0.05%

0.1% and 0.2%). Flow boiling heat transfer coefficients of these fluid versus vapor quality were measured respectively in a horizontal smooth tube under the mass flow density of 150

200

250

300 kg·m-2·s-1. The results indicated that the presence of graphite enhanced the flow boiling heat transfer. A correlation for predicting the flow boiling heat transfer coefficient of nanorefrigerant/oil mixture with graphite was proposed and it agreed with 94.5% of the experimental data within a deviation of ±15%.