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

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

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

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Heat Transfer Su Yongkang School of Mechanical Engineering # 4 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

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Heat Transfer Su Yongkang School of Mechanical Engineering # 5 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

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Heat Transfer Su Yongkang School of Mechanical Engineering # 6 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

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Heat Transfer Su Yongkang School of Mechanical Engineering # 7 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: T m will change if heat transfer is occurring! T m increases if heating occurs (T s > T m ) T m decreases if cooling occurs (T s < T m ) roro

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Heat Transfer Su Yongkang School of Mechanical Engineering # 8 Internal Flow (Contd) For constant heat flux: For constant wall temperature Sections 8.4 and 8.5 contain correlation equations for Nusselt number T x T x T x

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

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Heat Transfer Su Yongkang School of Mechanical Engineering # 10 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 9.30- 9.32. (P513) Please refer to problem 9.34. For vertical surface, transition to turbulence at Ra x 10 9

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

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Heat Transfer Su Yongkang School of Mechanical Engineering # 12 Discussion on the U Equation 11.5 For the unfinned, concentric, tubular heat exchangers. When the inner tube surface area is the reference calculating area. Example 11.1 Notice!

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

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