Abstract Enhancement of heat transfer to the fluid can be done by turbulence promoters such as attached fins to the pipe walls. In this study, the flow field and the heat transfer rates were numerically investigated in a pipe with an internally attached fin. Numerical sim- ulations were conducted for four different types of fluids and for different fin heights and locations, and as the Reynolds number was varied, the effects of the fin on Nusselt number and friction factors were investi- gated. For all the Reynolds numbers considered in this study, the effect of fin location on the heat transfer rate and friction factor was negligible. As the fin height was increased, the mean Nusselt number and the friction factor also increased in the turbulent flow regimes. For low Prandtl number fluids (Pr = 0.011), the main heat transfer mode is conduction, and hence the mean Nusselt number slightly affected the flow rates. List of symbols D diameter h fin height h conv convection heat transfer coefficient k turbulent kinetic energy k cond conduction heat transfer coefficient k fluid heat transfer coefficient of fluid L c considered length of pipe L ent entrance length L ex exit length L f fin location from z =0 Pr Prandtl number r + dimensionless distance Dr p nearest grid point distance to wall R radius of pipe Re Reynolds number T temperature T + dimensionless temperature T bulk bulk temperature T w wall temperature T 0 inlet temperature u r r velocity component u z z velocity component U 0 inlet velocity Greek symbols  turbulent kinetic energy dissipation l viscosity l eff effective viscosity l t turbulent viscosity q density r n,t turbulent Prandtl number s w wall shear stress 1 Introduction Laminar and turbulent flows in pipes are encountered in many engineering applications. A number of experimental and numerical studies were performed over the years to examine effects of attached-fins or N. Dinler (&) Æ N. Yucel Department of Mechanical Engineering, Faculty of Engineering and Architecture, Gazi University, Maltepe, 06570 Ankara, Turkey e-mail: ndinler@gazi.edu.tr Heat Mass Transfer (2007) 43:817–825 DOI 10.1007/s00231-006-0172-0 123 ORIGINAL Flow and heat transfer in a pipe with a fin attached to inner wall Nureddin Dinler Æ Nuri Yucel Received: 6 January 2006 / Accepted: 29 June 2006 / Published online: 28 July 2006 Ó Springer-Verlag 2006