The transitional flow regime has been mostly avoided by
designers due to uncertainty and perceived chaotic behavior.
Previous work done in the transitional flow regime did not focus
specifically on the effects of free convection on the local heat
transfer characteristics along the tube length. Therefore, the
purpose of this study was to investigate the effects of free
convection on the heat transfer characteristics of developing and
fully developed flow in the transitional flow regime; and is work
in progress. An experimental set-up was designed, built and
validated and heat transfer measurements were taken at a heat
fluxes of 1, 3 and 8 kW/m2 between Reynolds numbers of 100
and 8 000. The Nusselt numbers varied between 4.3 and 80, the
Prandtl number between 2.9 and 6.5, the Grashof number
between 6.8 and 1.06x104 and the Rayleigh number between
43.8 and 3.07x104. It was found that the width of the transitional
flow regime decreased along the tube length as the flow
approached fully developed flow. As the free convection effects
were increased by increasing the heat flux, the width of the
transitional flow regime decreased further.
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .