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HEAT TRANSFER

Final Review. HEAT TRANSFER. Final Review Session. Viscous Flow. The Navier-Stokes Equations Nonlinear, second order, partial differential equations. Couette Flow, Poiseuille Flow. Convection. Basic heat transfer equation

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HEAT TRANSFER

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  1. Final Review HEAT TRANSFER # 1

  2. Final Review Session # 2

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

  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 # 4

  5. y 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 # 5

  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 # 6

  7. ro 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: Tmwill change if heat transfer is occurring! • Tmincreases if heating occurs (Ts > Tm) • Tmdecreases if cooling occurs (Ts < Tm) # 7

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

  9. Free (Natural) Convection • Grashof numberin natural convection is analogous to the Reynolds number in forced convection Unstable,Bulk fluid motion Stable,No fluid motion Natural convection can be neglected Natural convection dominates # 9

  10. Free (Natural) Convection Rayleigh number: For relative magnitude ofbuoyancy 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 Rax 109 # 10

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

  12. 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. • When the inner tube surface area is the reference calculating area. # 12

  13. Discussion on the problems # 13

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