Compound thermal performance of an arc-shaped inner finned tube equipped with Y-branch inserts

Highlights: • Develop arc-shaped inner finned tube with Y-branch insert to improve heat transfer. • Compound thermal performance of the finned tube with Y-branch insert is evaluated. • Nusselt number is about 15.7–86.2% higher than that of the finned tube alone. • Arc-shaped inner finned tube with Y-branch insert performs better than others. -- Abstract: A novel arc-shaped inner finned tube with Y-branch inserts was proposed to further enhance the tube side's thermal performance. The compound thermal performances of the arc-shaped inner finned tube with Y-branch inserts were experimentally studied by comparing with the smooth tube and the arc-shaped inner finned tube. Experimental results indicate that the Nusselt number of the arc-shaped inner finned tube with Y-branch inserts is enhanced by ∼3.7 times that of the smooth tube and is approximately 15.7–86.2% higher than that of the arc-shaped inner finned tube depending on Reynolds number and space length (S). The friction factor of arc-shaped inner finned tube with Y-branch inserts with S = 10 cm, 15 cm and 20 cm are respectively 2.22–3.11, 2.1–2.73, 2.07–2.34 times as that of the arc-shaped inner finned tube. It is also found that the Nusselt number, friction factor and performance evaluation criterion of the arc-shaped inner finned tube with Y-branch insert increases with decreasing of the space length. Moreover, the performance evaluation criterion for the arc-shaped inner finned tube with Y-branch insert is about 1.02–2.22 while it is approximately 1.17–1.55 for the arc-shaped inner finned tube, which means that the arc-shaped inner finned tube with Y-branch inserts yields excellent overall thermal performance. Compared with other single and compound enhanced structures, the novel arc-shaped inner finned tube with Y-branch inserts can exchange more heat at the same pumping power. Finally, the empirical correlations for Nusselt number and friction factor are proposed according to the experimental results.