国上双人李 “-H Heat Transfer Coefficients in Heat Conduction Problem Heat transfer coefficient was often used as a boundary condition in conduction problems: Introduction to Convection: ·Local Heat Flux and Heat Transfer Coef佰icient T Flow and Thermal Considerations 4=(T-T) ·wverage Heat具and Heat Transfer AT. Coefficient for a Uaiform Surface Temperature: 9=4d,-(亿-J、d4 Chapter Six and AppendixD Newton's Cooling Law Sections 6.1 through 6.8 和教侧 and D.1 through D.3 ◆q=4亿-) 用上4生 工雅快物德辆九所 The Objectives of Heat Convection Study Velocity Boundary Layer:Physical Features We have taken the convection coefficient as a given,with little thought of 一m where the particular numbers come from. btedndace The central objective of comective heat trangfer is to understand the hear s山en mysteries of the heat transfer coefficient: What factors affect the convective heat transfer coefficient? -A region between the surface 6→-0.9 。 (correlations of heat transfer coefficieat) -Why does increase in the flow direction? -Manifestod by a surface shear stress that provides a drag force. -How does 霸上4生 工塑路物液研丸所 ©上生 工童前藏祸克所 Thermal Boundary Layer:Physical Features Boundary Laver Transition T F牌em一a laminar region? 自 ·What are the ch of turbulent region - 自身 ciated Aregion between the suface and 4→=1.09 turbulent flow? - -Why does increase in the flow direction? I0sRes3×10 critical Reynolds namber Nomuily:Re5x10 ansf品coefficient。 -0 xlocation at which transition o turbulence begins -If (T,-T.)is constant,how do g;and 闭上生 11 Introduction to Convection: Flow and Thermal Considerations Chapter Six and Appendix D Sections 6.1 through 6.8 and D.1 through D.3 Heat Transfer Coefficients in Heat Conduction Problem • Local Heat Flux and Heat Transfer Coefficient:   s s q hT T    Heat transfer coefficient was often used as a boundary condition in conduction problems: 工程热物理研究所 • Average Heat Flux and Heat Transfer Coefficient for a Uniform Surface Temperature:   s s q hA T T    s A s q q dA      s  T T hdA s   A s 1 s A s s h hdA A   Newton’s Cooling Law • We have taken the convection coefficient as a given, with little thought of where the particular numbers come from. • The central objective of convective heat transfer is to understand the mysteries of the heat transfer coefficient: What factors affect the convective heat transfer coefficient? The Objectives of Heat Convection Study 工程热物理研究所 How do these factors influence the convective heat transfer coefficients? (correlations of heat transfer coefficient) How to enhance heat transfer (increase heat transfer coefficient)? Velocity Boundary Layer : Physical Features – A consequence of viscous effects associated with relative motion between a fluid and a surface. – A region of the flow characterized by shear stresses and velocity gradients.   0 99 u y    – A region between the surface and the free stream whose 工程热物理研究所 – Why does increase in the flow direction?  – How does vary in the flow direction? Why? s  0.99 u   and the free stream whose   thickness increases in the flow direction.  s y 0 u y       – Manifested by a surface shear stress that provides a drag force. s  – A consequence of heat transfer between the surface and fluid – A region of the flow characterized by temperature gradients and heat fluxes.  – A region between the surface and h f h hi k T Ty    Thermal Boundary Layer : Physical Features 工程热物理研究所 – Why does increase in the flow direction? t  t the free stream whose thickness  increases in the flow direction.   0.99 s t s T Ty T T      – Manifested by a surface heat flux and a convection heat transfer coefficient h . s q s f y 0 T q k y       0 / '' f y s s s q kT y h TT TT          – If is constant, how do and h vary in the flow direction?   T T s   s q Boundary Layer Transition • What are the characteristics of laminar region? • What are the characteristics of turbulent region? • What conditions are associated with transition from laminar to turbulent flow? 工程热物理研究所 • Transition criterion for a flat plate in parallel flow: , Re critical Reynolds number c x c u x inertia vicous      location at which transition to turbulence begins c x  • Why is the Reynolds number an appropriate parameter for quantifying transition from laminar to turbulent flow? 5 6 , 10 Re 3 10   x c 5 Normally: Re 5 10 x c,  