HEAT TRANSFER CHAPTER 7 External flow 们au #1 Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 1 HEAT TRANSFER CHAPTER 7 External flow
External Flow: Flat Plate Topic of the day Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 2 External Flow: Flat Plate Topic of the Day
External Flow: Flat Plate Where we' ve been∴ General overview of the convection transfer equations Developed the key non-dimensional parameters used to characterize the boundary layer flow and convective heat and mass transfer hl N k Where were going Applications to external flow Flat plate Other shapes → Next time Then onto internal flow Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 3 External Flow: Flat Plate Where we’ve been …… • General overview of the convection transfer equations. • Developed the key non-dimensional parameters used to characterize the boundary layer flow and convective heat and mass transfer. Where we’re going: • Applications to external flow – Flat plate Today – Other shapes Next time Then onto internal flow …… f k h L Nu =
Differences between external and internal flow External flow Boundary layer develops freely without constraints Free strea olx Velocity boundar Internal flow: boundary layer is constrained and eventually merges #4 Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 4 Differences between external and internal flow • External flow: Boundary layer develops freely, without constraints • Internal flow: Boundary layer is constrained and eventually merges
How this impacts convective heat transfer Recall the boundary layer convection equations Free stream 6(x) Thermal boundary T≠T oT temperature fluid thermal gradient conductivity As you go further from the leading edge, the boundary layer continues to grow. Assuming the sur face and freestream t do not change with increasing distance x' boundary layer thickness. 8.1 aT ano gs Also Heat Transfer Su Yongkang School of Mechanical Engineering
Heat Transfer Su Yongkang School of Mechanical Engineering # 5 How this impacts convective heat transfer • Recall the boundary layer convection equations: • As you go further from the leading edge, the boundary layer continues to grow. Assuming the surface and freestream T do not change: with increasing distance ‘x’: – Boundary layer thickness, , – so – and fluid thermal conductivity wall temperature gradient Ts T Also =0 = − y s f y T q k =0 y y T s q