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Unformatted text preview: °C)3
0.729
(0.720 10 3 kg/m · s)(40 30)°C(0.03 m)
2
9292 W/m · °C hhorizontal 0.729 1/4 The heat transfer surface area of the pipe per unit of its length is As
DL
(0.03 m)(1 m) 0.09425 m2. Then the rate of heat transfer during this condensation process becomes ·
Q hAs(Tsat Ts) (9292 W/m2 · °C)(0.09425 m2)(40 30)°C 8758 W (b) The rate of condensation of steam is ·
m condensation ·
Q
h*
fg 8578 J/s
2435 103 J/kg 0.00360 kg/s Therefore, steam will condense on the horizontal tube at a rate of 3.6 g/s or
12.9 kg/h per meter of its length. EXAMPLE 10–7 Condensation of Steam on Horizontal Tube Banks Repeat the proceeding example problem for the case of 12 horizontal tubes
arranged in a rectangular array of 3 tubes high and 4 tubes wide, as shown in
Figure 10–33. SOLUTION (a) Condensation heat transfer on a tube is not influenced by the
presence of other tubes in its neighborhood unless the condensate from other
tubes drips on it. In our case, the horizontal tubes are arranged in four vertical
tiers, each tier consisting of 3 tubes. The average heat transfer coefficient for a
vertical tier of N horizontal tubes is related to the one for a single horizontal
tube by Eq. 10–33 and is determined to be
Condensate
flow 1
h
N1/4 horiz, 1 tube hhoriz, N tubes FIGURE 10–33
Schematic for Example 10–7. 1
(9292 W/m2 · °C)
31/4 7060 W/m2 · °C Each vertical tier consists of 3 tubes, and thus the heat transfer coefficient determined above is valid for each of the four tiers. In other words, this value can
be taken to be the average heat transfer coefficient for all 12 tubes.
The surface area for all 12 tubes per unit length of the tubes is As Ntotal DL 12 (0.03 m)(1 m) 1.1310 m2 Then the rate of heat transfer during this condensation process becomes ·
Q hAs(Tsat Ts) (7060 W/m2 · °C)(1.131 m2)(40 30)°C (b) The rate of condensation of steam is again determined from 79,850 W cen58933_ch10.qxd 9/4/2002 12:38 PM Page 545 545
CHAPTER 10 ·
m condensation ·
Q
h*
fg 79,850 J/s
2435 103 J/kg 0.0328 kg/s Therefore, steam will condense on the horizont...
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This note was uploaded on 01/28/2010 for the course HEAT ENG taught by Professor Ghaz during the Spring '10 term at University of Guelph.
 Spring '10
 Ghaz

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