Turbulent heat transfer and temperature profiles in a rifled pipe

Abstract

Turbulent temperature profiles and heat transfer coefficients have been measured in an electrically heated 2 in. i.d. pipe with a 1 4 × 1 4 in, spiral rib of pitch/dia. ratio 2·58. Rifling resulted in greater than twofold increases in Stanton number St, but with a proportionate increase in friction factor C F , which is dependent on Re. Logarithmic plots of St/C F against Re show the rifled tubes to be generally less efficient than smooth tubes, although the efficiencies for air are considerably closer together than those for water. Dimensionless temperatures t + were obtained and show the temperature profile to be almost flat in the turbulent core for both water and air. This is consistent with the greater relative efficiency for air since proportionately more of the resistance is found in the turbulent core with fluids of low Prandtl number. These results suggest that rifled tubes might be used to ensure uniform radial temperatures in tubular reactors.