CHEMICAL ENGINEERING

130 CHEMICAL ENGINEERING VOLUME 1 SOLUTIONS

Film coefficients

Inside:

hidi/kD 0. 023 

dG^0 /^0.^8 

Cp/k^0.^4 (equation 9.61)

diD12 mm or 1. 2 ð 10 ^2 m.

The mean air temperatureD 0. 5

366 C 283 D325 K andkD 0 .029 W/m K.

Cross-sectional area of one tubeD

$/ 4

1. 2 ð 10 ^22 D 1. 131 ð 10 ^4 m^2

Area for flowD 

20 ð 201. 131 ð 10 ^4 D 4. 52 ð 10 ^2 m^2.

Thus, mass velocityGD 0. 9 /

 4. 52 ð 10 ^2 D 19 .9 kg/m^2 s.

At 325 K,D 0 .0198 mN s/m^2 or 1. 98 ð 10 ^5 Ns/m^2

CpD 

1. 0 ð 103 J/kg K

Thus:
hið 1. 2 ð 10 ^2 /
2. 9 ð 10 ^2 D 0. 023

1. 2 ð 10 ^2 ð 19. 9 / 1. 98 ð 10 ^50.^8

ð 

1. 0 ð 103 ð 1. 98 ð 10 ^5 / 0. 0290.^4

0. 4138 hiD 0. 023

1. 206 ð 1040.^8

0. 6830.^4 and hiD 87 .85 W/m^2 K

Outside:

hodo/kD 0. 33 Ch

doG^0 /^0 max.^6 

Cp/k^0.^3 (equation 9.90)

doD 12 .0mm or 1. 2 ð 10 ^2 m

G^0 D10 kg/m^2 s for free flow

G^0 maxDYG^0 /

Ydo

whereY, the distance between tube centresD 2 doD 2. 4 ð 10 ^2 m.

∴ G^0 maxD
2. 4 ð 10 ^2 ð 10. 0 /
2. 4 ð 10 ^2  1. 2 ð 10 ^2 D20 kg/m^2 s

At a mean flue gas temperature of 0. 5

700 C 366 D533 K,

D 0 .0286 mN s/m^2 or 2. 86 ð 10 ^5 Ns/m^2 , kD 0 .045 W/m K and CpD

1. 0 ð
   103 J/kg K

∴ RemaxD

1. 2 ð 10 ^2 ð 20. 0 /


2. 86 ð 10 ^5 D 8. 39 ð 103

From Table 9.3, whenRemaxD 8. 39 ð 103 ,XD 2 do,andYD 2 do,ChD 0 .95.

Thus:
hoð 1. 2 ð 10 ^2 /
4. 5 ð 10 ^2 D
0. 33 ð 0. 95
8. 39 ð 1030.^6

ð 

1. 0 ð 103 ð 2. 86 ð 10 ^5 / 0. 0450.^3

or: 0. 267 hoD 0. 314
8. 39 ð 1030.^6
0. 8360.^3 and hoD232 W/m^2 K

Overall:
Ignoring wall and scale resistances, then:
1 /UD 1 /hoC 1 /hiD
0. 0114 C 0. 0043 D 0. 0157

and: UD 63 .7W/m^2 K