HEAT TRANSFER chAPTER 8 Internal flow 们au Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 1 HEAT TRANSFER CHAPTER 8 Internal flow
Internal flow Heat Transfer Where we’ ve been. Introduction to internal flow, boundary layer growth, entry effects Inviscid flow region Boundary layer region ro Hydrodynamic entrance region Fully developed region Where were going Developing heat transfer coefficient relationships and correlations for internal flow Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 2 Internal Flow Heat Transfer Where we’ve been …… • Introduction to internal flow, boundary layer growth, entry effects Where we’re going: • Developing heat transfer coefficient relationships and correlations for internal flow ro
Internal flow Heat Transfer KEY POINTS THIS LECTURE Energy balance for internal flow in a tube Temperature and heat transfer relations for two cases Constant surface heat flux Constant surface temperature Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 3 Internal Flow Heat Transfer KEY POINTS THIS LECTURE • Energy balance for internal flow in a tube • Temperature and heat transfer relations for two cases: – Constant surface heat flux – Constant surface temperature
Basic concepts-thermal considerations 1. The mean temperature viscid flow regio Boundary layer region l Hydrodynamic entrance region Fully developed region fd力 For the internal energy puc,l4.andE,≡ mc T So SJ puc TdA puc,TdA C nc pumAc For incompressible flow in a circular tube 2 Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 4 Basic concepts—thermal considerations • 1. The mean temperature • For the internal energy • So • For incompressible flow in a circular tube, ro = Ac t v TdAc E uc t v Tm E m c and m c v A v c v A v c m u A c uc TdA mc uc TdA T c c = = = 0 0 2 0 2 r m m uTrdr u r T
Basic concepts-thermal considerations 2. Newtons law of cooling qy=h(T。-Tmn Not constant Here, the mean t plays the same role as the free stream T for external flows 3. Fully developed conditions because of heat transfer, T(r) is continuousl changing with X can fully developed conditions be reached?? For thermally fully developed 0|T(x)-7(r,x) 0 OxLT。(x)-Tm(x) fa, t Although the temperature profile t(r) changes with x, the relative shape of the profile no longer changes Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 5 Basic concepts—thermal considerations • 2. Newton’s law of cooling • Here, the mean T plays the same role as the free stream for external flows. • 3. Fully developed conditions because of heat transfer, T(r) is continuously changing with x. can fully developed conditions be reached?? • For thermally fully developed • Although the temperature profile T(r) changes with x, the relative shape of the profile no longer changes. ( ) qs = h Ts −Tm T Not constant! 0 ( ) ( ) ( ) ( , ) , = − − m f d t s s T x T x T x T r x x