Air-water two-phase pressure drop in U-type wavy tubes

Two-phase frictional performance of air-water mixture flow in six horizontal U-type wavy tubes is presented. The inner diameters of the wavy tubes are 5.07 and 8.29 mm, whereas the curvature ratios span from 3.94 to ∼7.87. The two-phase superficial velocities for air and water are in the range of U_L,S = 0.02-0.7 m/s and U_G,S = 0.15-60 m/s. The measured pressure loss in bend included the loss in U bends and the loss caused by the distorted flow in the downstream straight tube. This leads to the definition of the equivalent frictional two-phase pressure gradient in the U bend. The ratio between the two-phase pressure gradient in the U-bend and the two-phase pressure gradient in the upstream straight tube is found in the range of 1.5-3 for most of the data. The ratios increase with gas quality due to consecutive accelerating/deaccelerating phenomenon caused by the wavy tube. The frictional two-phase multiplier in the U bend can be correlated by the use of the Chisholm correlation. By introduction of the Martinelli parameter and the liquid Froude number to the Chisholm correlation, a new correlation is proposed that can describe the present φ_B,L ² data with a mean deviation of 13.9%.