Single-phase and two-phase frictional craracteristics of small U-type wavy tubes

This Study presents single-phase and two-phase frictional characteristics inside small diameter wavy tubes. A total of twelve tubes was used for testing. The ranges for the geometric parameters of the tested wavy tubes are diameter D = 3.43 - 8.29 mm, curvature ratio 2R/D = 3.70 - 7.87, and the ratio of the spacer length L/D = 1.93 - 30.5. For single-phase flow, the bend friction factor increases with the decrease of curvature ratio and spacer length. A friction factor equation is developed based oil the experimental data with characterizing parameters like 2R/D, L/D, new Dean number, and Reynolds number. A fair agreement of the f(C) data and the predictions with a mean deviation of 10.07% is observed. The frictional two-phase multiplier in U bend can be correlated by using the Chisholm correlation. By introducing the Martinelli parameter and the liquid Froude number to the Chisholm correlation, a new correlation is proposed that can describe the frictional multiplier data, with a mean deviation of 15.86% based on the preset 574 data and the authors' previously reported 279 data. (C) 2004 Elsevier Science Ltd.