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where k l is termed the overall heat transfer coefficient referenced to (or based on)
the inside tube heat transfer area", and d 1 and d 2 the inside and outside diameters of the

tube.
A temperature t S1 and t S2 on the surfaces of cylinder wall is determined:

q 1 q 1 d
t  t  l ; t  t  l ln 2 . (2.8)
1 c 1 p c 2 1 c
  d  2 d
1 1 1

In the case of multi-layered cylinder wall:

1
k  (2.8)
l n
1 1 d 1
  ln  i 1 
 d 2 d  d
1 1  i 1 i i 2 n 1

Determine the overall heat transfer coefficient k for heat transfer occurring from

superheated steam in a steel pipe to atmosphere, with the following conditions.

Pipe nominal size = 8″

pipe schedule = STD

0
Average steam temperature over the pipe length = 200 C
0
Ambient air temperature = 22 C
2
heat transfer coefficient on steam side = α S = 0.08 W/m K
2
heat transfer coefficient on air side = α A = 0.04 W/m K
conductivity‘λ’ of steel = 60 W/mK (at given temperature range)

From Cyclopedia’s standard piping dimensions calculator, for 8″ STD schedule pipe,

pipe inner diameter = d 1 = 202.72 mm = 0.20 m

pipe outer diameter = d 2 = 219.08 mm = 0.22 m

r 10 = 0.1 m and r 2 = 0.11 m

Using the given data and equation (4),

1 1 W
k    . 0 026
l 1 1 d 1 1 1 . 0 22 1 m 2 K
 ln 2   ln 
 d 2 d  d 0.08 0.2 2 60 2 . 0 . 0 04 . 0  22
1 1 1 2 2

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