The average Reynolds number for air passing in turbulent flow over a 2-m-long flat plate is 2.4 x 106. Under these conditions, the average Nusselt number was found to be equal to 4150. Determine the average heat transfer coefficient for an oil having thermal properties similar to those in Appendix 2, Table 18 at 30°C at the same Reynolds number and flowing over the same plate.
GIVEN
Turbulent flow of air over a flat plate
Average Reynolds number (ReL) = 2.4 x 106
Plate length (L) = 2 m
Average Nusselt number (Nu) = 4150
FIND
Average heat transfer coefficient
ASSUMPTIONS
Steady state
Fully developed turbulent flow
Transition from laminar to turbulent flow occurs at Rex = 5 x 105
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 18, for oil at 30°C
Thermal Conductivity (k) = 0.11 W/(m K)
Kinematic Viscosity (v) = 15.4 ? 10–6 m2/s
Thermal Diffusivity (a) = 707 ? 10–10 m2/s
The Prandtl number for the oil is
The empirical correlation from Table 5.5 can be used to find the Nusselt number for the oil.
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