Convection correlations:turbulent flow in circular tubes A lot of empirical correlations are available. For smooth tubes,the fully developed flow Heating: Nup =0.023Res Pr4 Cooling: Nup=0.023Res Pr03 For rough tubes,coefficient increases with wall roughness.For fully developed flows Nua (f/8)ReD-1000)Pr 1+12.7f18)2(Pr23-1) Consider the entry length Short tubes NuD≈Nup,fa NuD C =1+ Nup,fd (x/D)m For liquid metals,see textbook p461. Heat Transfer #7 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 Nu D  NuD, fd or m D fd D x D C Nu Nu ( / ) 1 ,   Short tubes