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# HEAT TRANSFER Final Review # 1.

## Presentation on theme: "HEAT TRANSFER Final Review # 1."— Presentation transcript:

HEAT TRANSFER Final Review # 1

Final Review Session # 2

Viscous Flow The Navier-Stokes Equations
Nonlinear, second order, partial differential equations. Couette Flow, Poiseuille Flow. # 3

Convection Basic heat transfer equation
Primary issue is in getting convective heat transfer coefficient, h h relates to the conduction into the fluid at the wall average heat transfer coefficient # 4

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 For mixed laminar and turbulent flow over flat plate y # 5

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 # 6

Convection with Internal Flow
Main difference is the constrained boundary layer 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 ) ro # 7

Internal Flow (Cont’d)
For constant heat flux: For constant wall temperature Sections 8.4 and 8.5 contain correlation equations for Nusselt number T x T x # 8

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 Natural convection dominates # 9

Free (Natural) Convection
Rayleigh number: For relative magnitude of buoyancy and viscous forces 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 (P513) Please refer to problem 9.34. For vertical surface, transition to turbulence at Rax  109 # 10

Heat Exchangers Example: Shell and Tube: Cross-counter Flow
Two basic methods discussed: LMTD Method -NTU Method # 11

Discussion on the U Notice! Example 11.1 Equation 11.5
For the unfinned, concentric, tubular heat exchangers. When the inner tube surface area is the reference calculating area. # 12

Discussion on the problems
# 13

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