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

A numerical study was undertaken for developing turbulent mixed convection in a horizontal circular tube with strip-type inserts (longitudinal strip L S and crossed-strip CS inserts) for 6500 less than or equal to Re less than or equal to 19 500 and 0 less than or equal to Gr less than or equal to 10 (8). The turbulence model used is a standard Version of k-epsilon model wit h wall functions. Three-dimensional Navier-Stokes equations were solved usi ng some modifications to the SIMPLE solution procedure. Temperature data an d heat transfer coefficients at different heat flux levels were calculated and correlated in terms of relevant parameters. The buoyancy effect was exa mined in detail for 0 less than or equal to Gr/Re-2 less than or equal to 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 enhancemen t was found to be 2-3 times that of bare tubes. The results were also compa red with those from the corresponding previous experimental data. A good ag reement was found. (C) 2001 Elsevier Science Ltd. All rights reserved.