Spirally-fluted tubes and enhanced tubes in confined crossflow. Part 1. Flow inside fluted tubes. Final report, August 1987-September 1990

An experimental investigation was conducted for single-phase flow inside spirally fluted tubes. The friction factor and Nusselt number data were obtained for the laminar, transition, and turbulent flow regimes. Fourteen fluted tubes were tested to cover a wide range of geometrical parameters of the flutes. In addition, a qualitative study on the flow phenomena was conducted through flow-visualization tests. Friction factor enhancements in the laminar regime were typically between 1.2 and 3.0, while enhancement values of up to 9 were recorded in the transition regime. In the turbulent regime enhancement, factors were in the range of 2.0 and 6.0. Nusselt numbers in the laminar and transition regime were between 2 and 10 times the smooth tube values, while turbulent enhancements were between 1.1 and 2.5. In the laminar and transition regimes, the increase in heat transfer was up to two times greater than the increase in friction factor. The friction factors and Nusselt numbers were found to be functions of the flute depth, pitch and helix angle. The friction factor data obtained consisted of 507 data points. Friction factors were correlated as a function of Reynolds number (3000 = or < Re = or < 15,000) and other nondimensional geometricalmore » parameters.« less