Heat transfer coefficients for laminar to turbulent flow in tubes at constant heat flux

Abstract

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.

Due to constraints and changes in operating conditions, heat exchangers are often forced to operate under conditions of transitional flow. However, the heat transfer and flow behavior in this regime is relatively unknown. By describing the transitional characteristics it would be possible to design heat exchangers to operate under these conditions and improve the efficiency of the system. This study was aimed at obtaining experimental data for water flowing through a smooth tube with an inner diameter of 8 mm under constant heat flux conditions. Four heat flux test cases were considered namely: 1 409, 3 354, 5 009 and 6 881 W/m2. The experiments covered a Reynolds number range of 500 to 8 800, a Prandtl number range of 4 to 7, a Nusselt number range of 6 to 67, and a Grashof number range of 750 to 25 600. Experiments have shown a smooth transition from laminar to turbulent flow.