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S 18 CHAPTER 4 PHYSICAL FUNDAMENTALS
Example 2
Heat transfer coefficient between a pipe and a wall. Water flows in a pipe
(d s=- 15 mm) with a velocity of v = 1.0 m s~ . The mean temperature of wa-
ter is 9 m = 15 °C, and the wall temperature 6 $ — 50 °C. Calculate the heat
transfer coefficient away from the pipe inlet. For water the properties are
3
3
1
1
ij 15o C = 1.14 x 10~ kg nrV , i) 50o C = 0.54 x 10~ kg nTV , c p]5^ =
1
1
1
4.2kJkg~ KT , and A 15o C = 0.60 W m^K' , with turbulent flow. The
Nusselt number equation is
The flow is turbulent, Re > 2300, and thus the part of Eq. (4.201) that
considers the inlet flow region ~ 1 can be ignored.
4.3.5 Thermal Radiation
4.3.5.1 Planck's Law of Radiation
Total heat transfer consists of radiation at different frequencies. The dis-
tribution of radiation energy in a spectrum and its dependency on temperature
is determined from Planck's law of radiation. M OTJ/and M wA are the spectral ra-
diation intensities for a blackbody:
