CHEMICAL ENGINEERING

128 CHEMICAL ENGINEERING VOLUME 1 SOLUTIONS

Solution

At 101.3kN/m^2 , benzene condenses atTsD353 K. With a wall temperature ofTwD
300 K, the film properties at a mean temperature of 327 K are:

D 4. 3 ð 10 ^4 Ns/m^2 ,D860 kg/m^3 ,kD 0 .151 W/m K and

D423 kJ/kgD 4. 23 ð 105 J/kg

Thus:

sDf[4k

TsTwx]/

gsin^2 g^0.^25 (equation 9.168)

Df[4ð 4. 3 ð 10 ^4 ð 0. 151

353  300 x]/

 9 .81 sin 45°ð 4. 23 ð 105 ð 8602 g^0.^25

D 2. 82 ð 10 ^4 x^0.^25 m

Similarly:

hDf

^2 gsink^3 /[4

TsTwx]g^0.^25 (equation 9.169)

Df 

8602 ð 9 .81 sin 45°ð 4. 23 ð 105 ð 0. 1513 /[4ð 4. 3 ð 10 ^4

353  300 x]g^0.^25

D 535 x^0.^25 W/m^2 K

Va l u e s o fxbetween 0 and 2.0 m in increments of 0.20 m are now substituted in these
equations with the following results, which are plotted in Fig. 9b.

0.25

0.20

0.15

0.10

0.05

0 0.2

750

800

700

650

600

550

500

450

0.4 0.6 0.8 1.0 1.2 1.4 1.6

Distance from top of surface (x m)

Thickness of film (

s mm)

Heat transfer coefficient (

h W/m

2 K)

Figure 9b.