CHEMICAL ENGINEERING

186 CHEMICAL ENGINEERING VOLUME 1 SOLUTIONS

With scale

hiD 5. 265 u^0.^8 kW/m^2 K, scale resistanceD 0 .20 m^2 K/kW

and: 1 /UD 1 /
5. 265 u^0.^8 C 0. 20 C
1 / 2. 25

∴ UDu^0.^8 /
0. 190 C 0. 644 u^0.^8 kW/m^2 K

that is: QD1600 kW as before.

The mass flow of water is:
uð 0. 0456 ð 1000 D 45. 6 ukg/s and the outlet water
temperature is given by:

1600 D 45. 6 uð 4. 18 

T 290

or: TD
290 C 8. 391 /uK

 1 D 

350  290 D60 deg K, 2 D 

350  290  8. 391 /uD 

60  8. 391 /u

and:mD
60 
60  8. 391 /u/ln[60/
60  8. 391 /u]

D 8. 391 /fuln[60u/

 60 u 8. 391 ]g

In equation 9.1:

1600 D[u^0.^8 /

 0. 190 C 0. 644 u^0.^8 ]ð 20. 74 ð 8. 391 /fuln[60u/

 60 u 8. 391 ]g

or: 1 /fu^0.^2
0. 190 C 0. 644 u^0.^8 ln[60u/
60 u 8. 391 ]gD 9. 194

The left-hand side of this equation is plotted againstuin Fig. 9e and the function equals
9.194 whenuD 2 .06 m/s.

8.0

8.2

8.4

8.6

8.8

9.0

9.2 9.194

0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

2.06

Water velocity (u m/s)

Function

Figure 9e.