Fluid Flow and Mass Transfer in a Sinusoidal Wavy-Walled Tube at Moderate Reynolds Numbers.

Abstract

Fluid flow and mass transfer characteristics in an axisymmetric sinusoidal wavy-walled tube are investigated experimentally in the Reynolds number range from 50 to 1 000. The attention is paid to the transitional flow, which is observed in the Reynolds number range of 160 to 200. In the laminar flow regime wall shear stress and mass transfer rate increase with the slope of 1 and 1/3, respectively, whereas in the turbulent flow regime they increase with the slope of 3/2 and 3/5, respectively. In the transitional flow regime they increase dramatically with a sharp slope. It is found that lamiar-like motion and turbulent-like motion alternatively take place with different time intervals in this flow regime. This is quite different from the flow instability for the wavy-walled channel, in which the Tollmien-Schlichting waves are observed. The flow instability in the wavy-walled tube is considered to be responsible for a significant increment of the wall shear stress and mass transfer rate in the transitional flow regime.