Chapter 8: Internal Forced Convection

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Entry Lengths ()– HydrodynamicLaminar flowL≈ ⋅ D (8-11)h,laminar0.05Re– ThermalL ≈ 0.05Re⋅Pr⋅ D= Pr⋅ L (8-12)t,laminarh,laminar– HydrodynamicTurbulent flowL14= D⋅ (8-13),1.359 Reh turbulent– Thermal(approximate)L ≈ L ≈ D (8-14)h, turbulent t, turbulent10
Turbulent flow Nusselt Number• The Nusselt numbers are muchhigher in the entrance region.• The Nusselt number reachesa constant value at a distanceof less than 10 diameters.• The Nusselt numbers for theuniform surface temperature and uniform surface heatflux conditions are identical in the fully developedregions, and nearly identical in the entrance regions. Nusselt number is insensitive to the type ofthermal boundary condition.
Page 1: Chapter 8:Internal Forced Convectio
Page 4 and 5: Average Velocity• The value of th
Page 6 and 7: • For incompressible flow in a ci
Page 8 and 9: The Entrance Region• A fluid ente
Page 10 and 11: Thermal Entrance Region• Consider
Page 12 and 13: • Surface heat flux can be expres
Page 16 and 17: General Thermal Analysis• In the
Page 18 and 19: • In the fully developed region,
Page 20 and 21: Constant Surface Temperature• The
Page 22 and 23: • The temperature difference betw
Page 24 and 25: Laminar Flow in TubesAssumptions:
Page 26 and 27: • Taking the limit as dr, dx 0 g
Page 28 and 29: • Combining the last two equation
Page 30 and 31: • A pressure drop due to viscous
Page 32 and 33: • Or∂T1 ∂Qu =−( )∂ x ρc
Page 34 and 35: • Separating the variables and in
Page 36 and 37: Constant Surface temperature (circu
Page 38 and 39: - HydrodynamicLaminar flowLh,lamina
Page 40 and 41: Turbulent flow in Tubes• Most cor
Page 42: Moody Diagram

Chapter 8: Internal Forced Convection

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