Effect of Spacer Length between Consecutive Bends on Friction Factors of U-Type Wavy Tubes

Abstract

U-type wavy tubes are used in a great number of heat transfer equipment and flow transmitting devices. It provides a long flow path in a relatively small space and thereby allows the fluid flowing through the tube to have sufficient time for heat and mass transfer. Besides, vigorous mixing of fluid provided by the alternating bends enhances the heat and mass transfer processes. During fluid flow in U-type wavy tubes through consecutive bends, the flow phenomenon becomes more complex and the head loss increases. The present thesis work is undertaken to experimentally measure the head loss and the friction factor in U-type wavy tubes. A test rig has been designed and fabricated to determine the friction factor for small diameter flexible tubes of U-type wavy configuration using water as the working fluid. Experiments are done by varying the number of bends and the spacer length to study their effects on the bend friction factor. The range of the Reynolds number is 1000 to 23,500 and that of Dean number is 500 to 7000. It has been found that the bend friction factor decreases with the increase of Reynolds Numbers. At large values of Reynolds number, the differences in bend friction factors due to variations in spacer lengths or number of bends diminishes. The bend friction factor increases with the increase of the spacer length up to a certain value of the spacer length ratio. Beyond this value of the spacer length ratio, the bend friction factor stops changing. This spacer length ratio is termed as the critical spacer length ratio. In these experiments, the dimensionless critical spacer length ratio is found to be 15.2. This value of critical spacer length ratio is not affected by the number of bends The outcome of this study will be useful in designing fluid flow through U- type wavy tubes in various kinds of heat transfer equipment.