CHEMICAL ENGINEERING

HUMIDIFICATION AND WATER COOLING 327

350

300

250

200

150

100

50

280 290 300

Temperature (qK)

0 310 320 330

(qL 2 'HG 2 )

(qL 1 'HG 1 )

Enthalpy (

H

G

kJ /kg)

Figure 13b.

bulb temperature. From Fig. 13.4, at 295 K and 60% humidity, the wet-bulb temperature
of the inlet air is 290 K and at the best water might be cooled to 291 K. In the present
case, therefore, 291 K will be chosen as the water outlet temperature.

Thus an operating line of slope:LCL/GD 1 .66 and bottom coordinates:L 1 D291 K
andHG 1 D 47 .5 kJ/kg is drawn as shown in Fig. 13c. At the top of the operating line:

L 2 D330 K andHG 2 D 112 .5kJ/kg

As an alternative to the method used in Problem 13.8, the approximate method of Carey
and Williamson (equation 13.54) is adopted.

At the bottom of the column:

HG 1 D 47 .5kJ/kg,Hf 1 D 52 .0kJ/kg ∴H 1 D 4 .5kJ/kg

At the top of the column:

HG 2 D 112 .5kJ/kg,Hf 2 D382 kJ/kg ∴H 2 D 269 .5kJ/kg

At the mean water temperature of 0. 5  330 C 291 D 310 .5K:

HGmD 82 .0kJ/kg,HfmD 152 .5kJ/kg ∴HmD 70 .5kJ/kg

∴ Hm/H 1 D 15 .70 andHm/H 2 D 0. 262

and from Fig. 13.17:fD 0 .35 (extending the scales)