Convection correlations: turbulent flow in circular tubes A lot of empirical correlations are available For smooth tubes, the fully developed flow Nun=0.023 Re 4/5D0.4 Heating Cooling: Nup=0.023 Re 4/5D-0.3 For rough tubes, coefficient increases with wall roughness. For fully developed flows Nua-1+127/8)(P2 (f/8)ReD-1000 Consider the entry length Short tubes N uD NuD≈ND,fa or =1+ N D, fd (x/D) For liquid metals, see textbook p461 Heat Transfer Su Yongkang School of Mechanical EngineeringHeat Transfer Su Yongkang School of Mechanical Engineering # 7 Convection correlations: turbulent flow in circular tubes • A lot of empirical correlations are available. • For smooth tubes, the fully developed flow Heating: Cooling: • For rough tubes, coefficient increases with wall roughness. For fully developed flows • Consider the entry length • For liquid metals, see textbook p461. 4/5 0.4 0.023Re Pr NuD = D 4/5 0.3 0.023Re Pr NuD = D 1 12.7( /8) (Pr 1) ( /8)(Re 1000)Pr 1/ 2 2/3 + − − = f f Nu D d NuD  NuD, fd or m D f d D x D C Nu Nu ( / ) 1 , = + Short tubes