Ndenguma, D.D.Dirker, JacoMeyer, Josua P.2017-09-192017-09-192017http://hdl.handle.net/2263/62382Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .In this experimental study, the Reynolds number limits of the transitional flow regime and friction factor characteristics were determined in the transitional flow regime of annuli. Isothermal and diabatic tests were conducted using four horizontal concentric annular passages with hydraulic diameters of 26.2, 23, 20.2 and 17 mm and respective diameter ratios of 0.327, 0.409, 0.386 and 0.483. The water in the annular passage was either heated or cooled at non-uniform temperature on the inner wall while the outer wall was insulated. The flow was both hydrodynamic and thermally developing, and the transitional flow was associated with mixed convection. The geometric size of the annular passage had a significant influence on the friction factors and Reynolds number span of the transitional flow regime. The annular geometric parameter that represent the geometric size of the annular passage was proposed and found to describe the friction factors well. Subsequently, correlations for predicting the friction factors in the transitional flow regime were developed.6 pagesPDFenUniversity of PretoriaPressure dropTransitional flow regime of annuliMixed convectionPresentation