Chapter 8: Internal Forced Convection

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• A pressure drop due to viscous effects represents anirreversible pressure loss.• It is convenient to express the pressure loss for alltypes of fully developed internal flows in terms of thedynamic pressure and the friction factor L∆ PL= ( P1− P2)= f ⋅ ⋅Ddynamic pressurefriction factor 2ρVavg• Setting Eqs. 8–44 and 8–45 equal to each other andsolving for f gives2(8-45)– Circular tube, laminar:f64µ64= = (8-46)ρDVReavg
Temperature Profile and the Nusselt Number• Energy is transferred by mass in thex-direction, and by conduction in ther-direction.• The steady flow energy balance for a cylindricalshell element can be expressed as:mc T − mc T + Q− Q=• Substitutingp x p x+ dx r r+dr and dividing by 2πr dr dx gives, after rearrangingρcupc0( )(8-49)m= ρuA = ρu 2πrdr= 量流率Tx+ dx−Tx 1 Qr+dr−Qr( ) =−( )( )dx 2πrdx dr(8-50)
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 14 and 15: Entry Lengths ()- HydrodynamicLamin
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 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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