Investigation of turbulent flow and heat transfer in internally finned tubes

摘要

A numerical investigation of periodically fully-developed, steady, single-phase, turbulent flow and heat transfer in spirally finned tubes has been performed. A commercial computational fluid dynamics code named STAR-CD with an unstructured finite-volume method was employed to handle the complex geometry. The length-averaged friction factors and Nusselt numbers were compared with experimental data to validate the numerical schemes and turbulence models. The computational results match well with the experimental data.;The detailed flow fields and circumferentially local friction factors and Nusselt numbers are presented to explore the governing processes.;A parametric study systematically investigated the effects of the number of fins, helix angle, fin height, and fin width for tubes with a rectangular fin. In general, the Nusselt numbers and friction factors increase with an increase in these geometric parameters if the interfin passage is large enough. Increasing fin width (decreasing the size of the interfin passage) can cause the reverse effect depending on the absolute size of the interfin region. Which trend occurs depends on how the production of turbulent kinetic energy is affected by the geometry.;Three different fin shapes (rectangular, triangular, and round-crest) associated with three groups of number of fins, helix angle, fin height, and base fin-width were used to explore the effects of fin shape. The numerical results showed that the different fin shapes can cause 15% to 20% changes in Nusselt numbers and friction factors with some non-intuitive results. The physical reasons were explored in this investigation.