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The equation for the turbulent flow in a tube is given by [16]
where
n = 0.4 for heating
n = 0.3 for cooling
(3.54)
The following equation applies to laminar flow in a tube with a constant wall temperature
[3]
where
d{ = inside tube diameter
/ = tube length
The expression for the laminar flow heat transfer to flat plate is [3]
Equation 3.56 is valid for Pr = 0.6 to 2000 and Re < 10 5 .
The equation for turbulent flow heat transfer to flat plate is given as [3]
Equation 3.57 applies for the conditions:
Pr = 0.6 to 2000 and 5 • 10 5 < Re < 10 7 .
(3.55)
(3.56)
(3.57)
The properties of the fluids in the equations above are to be found at a mean fluid
temperature.
Example
A flat film is moving in a coating equipment at a velocity of 130 m/min on rolls that are
200 mm apart. Calculate the heat transfer coefficient a if the surrounding medium is air
at a temperature of 50 0 C.
Solution
The properties of air at 50 0 C are:
Kinematic viscosity v = 17.86 • 10" 6 m 2 /s
Thermal conductivity A = 28.22 • 10" 3 W/(m • K)
Prandtl number Pr = 0.69