TITLE.PM5

PSYCHROMETRICS 479

dharm

\M-therm\Th10-2.pm5

W

30 Cº

D B T

22 Cº

t = 18.6 Cdp º

Fig. 10.20
Example 10.17. 200 m^3 of air per minute at 15ºC DBT and 75% R.H. is heated until its
temperature is 25ºC.
Find : (i) R.H. of heated air.
(ii) Wet bulb temperature of heated air.
(iii) Heat added to air per minute.
Solution. Refer Fig. 10.21.
l Locate point 1 on the psychrometric chart on intersection of 15ºC DBT and 75% R.H.
lines.
l Through point 1 draw a horizontal line to cut 25ºC DBT line and get point 2.
l Read the following values from the psychrometric chart :
h 1 = 35.4 kJ/kg
h 2 = 45.2 kJ/kg
vs 1 = 0.8267 m^3 /kg.
(i)R.H. of heated air (read from chart) = 41%. (Ans.)
(ii)WBT of heated air (read from chart) = 16.1ºC. (Ans.)

(iii) Mass of air circulated per min., ma =

200

0 8267. = 241.9 kg.

∴ Heat added to air/min.

= ma (h 2 – h 1 ) = 241.9 (45.2 – 35.4) = 2370.6 kJ. (Ans.)