Flow boiling heat transfer in enhanced tubes with herringbone and dimple structure

• Flow boiling heat transfer of R32 in herringbone and dimple enhanced tubes are investigated. • Effects of mass flux, vapor quality and saturation temperature on heat transfer are investigated. • Heat transfer coefficient correlations for flow boiling in the enhanced tubes are developed. This paper experimentally investigates the flow boiling heat transfer characteristics of smooth tubes (ST) and advanced new enhanced tubes (HT and EHT) made of aluminum, using R32 refrigerant. The effects of the tubes on heat transfer coefficients (HTC) and frictional pressure drop during flow boiling were explored. The study examined the flow boiling heat transfer performance of the enhanced tubes and ST tubes under varying conditions of mass flux (100∼350 kg/m 2 s), saturation temperatures (279∼288 K), and refrigerant inlet vapor quality (0.1∼0.9), and analyzed the impact of the enhancement structures on flow boiling heat transfer. The results are that the HTC increases with rising saturation temperature, mass flux, and average vapor quality, with the HT tube exhibiting the best HTC, followed by the EHT tube. The result is that the frictional pressure drop increases with mass flux and average vapor quality and decreases with saturation temperature. Among them, the EHT tube exhibits the highest frictional pressure drop, while the pressure drop of the HT tube is closer to that of the ST tube. Additionally, four flow boiling heat transfer correlations were predicted the HTC of the ST tube, and the correlation with the best prediction results was selected to predict the HTC for the HT and EHT tubes. The revised correlation can verify over 95 % of the data within a ± 15 % range, establishing a new HTC correlation for enhanced tubes.