Heat transfer and friction coefficients for turbulent flow of air in smooth annuli at high temperatures

Abstract Local heat transfer and averaged friction coefficients were measured for subsonic turbulent flow of air through two smooth annuli, with diameter ratios equal to 1.99 and 1.38, respectively, having the inner tube heated up to temperatures of 1000°C. The main experimental results can be summarized as follows 1. 1. The local heat-transfer coefficients are correlated by: Nu B =0.018 D 2 D 1 0.16 Re 0.8 B Pr 0.4 B T W T E −0.2 which gives the Petukhov and Roizen correlation [13] for low temperature differences (TW/TE → 1). 2. 2. The average heat-transfer coefficients for the inner region of the annulus are correlated by: Nu B =0.0217 Re 0.8 B Pr 0.4 B T W T E −0.2 in excellent agreement with data for circular tubes (Dalle Donne-Bowditch correlation [1]). 3. 3. The friction coefficients, both for the whole annulus and the inner region of it, are in excellent agreement with the correlations of Maubach [26] obtained by integration of the universal velocity profile of Nikuradse, provided that density of the fluid is evaluated at the temperature Tx = √ (Tw · TB) and the kinematic viscosity at the temperature TW, as suggested by the experiments of Taylor for circular tubes [6].