Developing 3-D turbulent mixed convection in a circular duct inserted with longitudinal strips

Abstract

A numerical study was undertaken for developing turbulent mixed convection in a horizontal circular tube with strip-type inserts (longitudinal strip LS and crossed-strip CS inserts) for 6500⩽Re⩽19 500 and 0⩽ Gr⩽10 8. The turbulence model used is a standard version of k– ε model with wall functions. Three-dimensional Navier–Stokes equations were solved using some modifications to the SIMPLE solution procedure. Temperature data and heat transfer coefficients at different heat flux levels were calculated and correlated in terms of relevant parameters. The buoyancy effect was examined in detail for 0⩽ Gr/ Re 2⩽2.37. It is found that the buoyancy effect has less influence for tubes with inserts compared to the bare tubes. Moreover, the heat transfer enhancement was found to be 2–3 times that of bare tubes. The results were also compared with those from the corresponding previous experimental data. A good agreement was found.