ANALYSIS:The rate quation,for a unit length of the pipe,can be written as oym-1o) Rt where the thermal resistance is comprised of two elements, ,11 R财DDD 1,1 hi ho The convection cofficient for intemal flow,h,must be estimated from an appropriate correlation. From practical considerations,we recognize that the oil flow rate cannot be large enough to achieve turbulent flow conditions.Hence,the flow is am,and ifthe pipe is very long,the flow will be fully developed.The appropriate correlation is n p-366 h1=Nup kD=366x0.13W0.030m=162wm2K m.K The heat rate per unit length of the pipe is (150-20)°C =80.3W/m. < 1 1,1 m.K π(0.030m） 162+i W COMMENTS:This problem requires making a judgment that the oil flow will be laminar rather than turbulent.Why is this a reasonable assumption?Recognize that the correlation applies to a constant surface temperature condition. Heat Transfer #1 Su Yongkang School of Mechanical EngineeringHeat Transfer Su Yongkang School of Mechanical Engineering # 10