Influence of free convection on the heat transfer characteristics of developing and fully developed flow in the transitional flow regime

Abstract

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.