The characteristics of heat transfer for R290 flow boiling in 5 mm small diameter tubes were investigated experimentally with a focus on the effects of heat flux

mass flow rate

and saturation temperature on the surface coefficient of boiling heat transfer. The experimental conditions are as follows: heat flux=10–60 kW/m2; saturation temperature=15–25 ℃; mass flow rate=50–200 kg/(m2?s); and vapor quality=0.1–0.9. Results showed that an increase in heat flux can significantly enhance heat transfer and raise its surface coefficient

speeding up the dryout process and decreasing the starting vapor quality of dryout. Mass flow rate has slight influence on the surface coefficient of heat transfer at low vapor quality

whereas surface coefficient of heat transfer was positively correlated with mass flow rate at middle and high vapor quality. Moreover

the surface coefficient of heat transfer decreased with an enhancement in the saturation temperature with low heat flux at vapor quality range of 0.4–0.75

whereas it increased with an enhancement in the saturation temperature with higher heat flux.