Study of vapor liquid two-phase frictional pressure drop in a vertical heated spirally internally ribbed tube

Experiments of vapor liquid two-phase frictional pressure drop of upward flow boiling in a smooth tube and in a spirally internally ribbed tube were conducted, respectively. The spirally internally ribbed tube has an outside diameter of 22 mm and an inside diameter of 11 mm (an equivalent inside diameter of 11.6 mm) and the smooth tube has an outside diameter of 19 mm and an inside diameter of 15 mm. The test tubes were vertically installed and uniformly heated by electricity to achieve flow boiling test conditions. The available heated length of both test tubes is 2500 mm. The working fluids are water and kerosene, respectively. The experimental pressure is 6 bar for flow boiling of water and 3 bar for flow boiling of kerosene. The exit vapor quality of the test sections is about 0.3. The two-phase Reynolds number ranges from 8000 to 28,000. The experimental two-phase frictional pressure drops in the smooth tube are compared with the predicted results by the two-phase flow homogeneous model and the Friedel formula (Friedel, 1979. Improved friction pressure drop correlation for horizontal and vertical two-phase pipe flow. European Two-phase Flow Group Meeting, Ispra, Italy), respectively. It shows that the experimental results agree with the Friedel formula better than the two-phase flow homogenous model. By comparison, the two-phase frictional pressure drops in the spirally internally ribbed tube are 1.6–2.7 times greater than that in the smooth tube. A physical explanation of the increase of the two-phase frictional pressure drop in the spirally internally ribbed tube is given. According to the two-phase flow homogeneous model, a correlation of two-phase friction factor is proposed for the spirally internally ribbed tube and it is applicable to pressures up to 6 bar.