FORCED CONVECTION CORELATIONS
External Forced Convection Correlations
1. Flat Plate:
Local Nu ____ Laminar (x < xt)
Plate at
Uniform
Surface
Temperature
Local Nu ____ Turbulent (x > xt)
Average Nusselt Number
Limitation:
Plate at
Uniform
Surface
Temperature
with an
Insulated
Leading
Section
(length xo is
insulated)
Plate with
Uniform
Local Nu ____ Laminar
Local Nu ____ Turbulent
Local Nu ____ Laminar
Surface
Flux
OR
Local Nu ____ Turbulent
2. Cylinder
Average Nusselt Number
External
Flow
Normal to a
Cylinder
3. Sphere
Average Nusselt Number
External
Flow over a
Sphere
Internal Forced Convection Correlations
1. Entrance Region: Flow through Tubes at Uniform Surface Temperature
Fully
Developed
Average Nusselt Number
Velocity,
Developing
Temperature.
Laminar
Flow
Tmi and Tmo = mean temperatures at
the inlet and outlet
Average Nusselt Number
Developing
Velocity and
Temperature:
Laminar
Flow
The Colburn Equation
Its accuracy diminishes as the difference in
temperature between surface and fluid
increases.
Fully
Developed
Velocity and
Temperature
in Tubes:
Turbulent
Flow
The Gnielinski Equation
For fully developed flow set D/L = 0
u = mean fluid velocity
del p = pressure drop in a tube of length L
For smooth tubes
2. Non-circular Channels: Turbulent Flow
Correlation equations for turbulent flow through tubes can be applied to non-circular channels.
Af = flow area
P = wet perimeter