HEAT TRANSFER Final Review Heat Transfer 1 Su

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HEAT TRANSFER Final Review Heat Transfer #1 Su Yongkang School of Mechanical Engineering

HEAT TRANSFER Final Review Heat Transfer #1 Su Yongkang School of Mechanical Engineering

Final Review Session Heat Transfer #2 Su Yongkang School of Mechanical Engineering

Final Review Session Heat Transfer #2 Su Yongkang School of Mechanical Engineering

Viscous Flow • The Navier-Stokes Equations Nonlinear, second order, partial differential equations. • Couette

Viscous Flow • The Navier-Stokes Equations Nonlinear, second order, partial differential equations. • Couette Flow, Poiseuille Flow. Heat Transfer #3 Su Yongkang School of Mechanical Engineering

Convection • Basic heat transfer equation average heat transfer coefficient • Primary issue is

Convection • Basic heat transfer equation average heat transfer coefficient • Primary issue is in getting convective heat transfer coefficient, h • h relates to the conduction into the fluid at the wall Heat Transfer #4 Su Yongkang School of Mechanical Engineering

Convection Heat Transfer Correlations • Key is to fully understand the type of problem

Convection Heat Transfer Correlations • Key is to fully understand the type of problem and then make sure you apply the appropriate convective heat transfer coefficient correlation External Flow For laminar flow over flat plate y For mixed laminar and turbulent flow over flat plate Heat Transfer #5 Su Yongkang School of Mechanical Engineering

External Convection Flow For flow over cylinder Overall Average Nusselt number Table 7. 2

External Convection Flow For flow over cylinder Overall Average Nusselt number Table 7. 2 has constants C and m as f(Re) For flow over sphere For falling liquid drop Heat Transfer #6 Su Yongkang School of Mechanical Engineering

Convection with Internal Flow • Main difference is the constrained boundary layer ro •

Convection with Internal Flow • Main difference is the constrained boundary layer ro • Different entry length for laminar and turbulent flow • Compare external and internal flow: – External flow: Reference temperature: T is constant – Internal flow: Reference temperature: Tm will change if heat transfer is occurring! • Tm increases if heating occurs (Ts > Tm ) • Tm decreases if cooling occurs (Ts < Tm ) Heat Transfer #7 Su Yongkang School of Mechanical Engineering

Internal Flow (Cont’d) • For constant heat flux: T x • For constant wall

Internal Flow (Cont’d) • For constant heat flux: T x • For constant wall temperature T T x • Sections 8. 4 and 8. 5 contain correlation equations for Nusselt number Heat Transfer #8 x Su Yongkang School of Mechanical Engineering

Free (Natural) Convection Unstable, Bulk fluid motion Stable, No fluid motion • Grashof number

Free (Natural) Convection Unstable, Bulk fluid motion Stable, No fluid motion • Grashof number in natural convection is analogous to the Reynolds number in forced convection Natural convection can be neglected Heat Transfer #9 Natural convection dominates Su Yongkang School of Mechanical Engineering

Free (Natural) Convection Rayleigh number: For relative magnitude of buoyancy and viscous forces For

Free (Natural) Convection Rayleigh number: For relative magnitude of buoyancy and viscous forces For vertical surface, transition to turbulence at Rax 109 • Review the basic equations for different potential cases, such as vertical plates, vertical cylinders, horizontal plates (heated and cooled) • For horizontal plates, discuss the equations 9. 309. 32. (P 513) • Please refer to problem 9. 34. Heat Transfer # 10 Su Yongkang School of Mechanical Engineering

Heat Exchangers Example: Shell and Tube: Cross-counter Flow • Two basic methods discussed: 1.

Heat Exchangers Example: Shell and Tube: Cross-counter Flow • Two basic methods discussed: 1. LMTD Method 2. -NTU Method Heat Transfer # 11 Su Yongkang School of Mechanical Engineering

Discussion on the U • Equation 11. 5 Example 11. 1 Notice! • For

Discussion on the U • Equation 11. 5 Example 11. 1 Notice! • For the unfinned, concentric, tubular heat exchangers. • When the inner tube surface area is the reference calculating area. Heat Transfer # 12 Su Yongkang School of Mechanical Engineering

Discussion on the problems Heat Transfer # 13 Su Yongkang School of Mechanical Engineering

Discussion on the problems Heat Transfer # 13 Su Yongkang School of Mechanical Engineering