Honeywell AUTOMATIC CONTROL SI Edition, Engineering Manual

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ENGINEERING MANUAL OF AUTOMATIC CONTROL
PSYCHROMETRIC CHART FUNDAMENTALS
48
Figure 18 is the same as the chart shown in Figure 17 except
that it graphically displays the amount of heat added by the
process. Enthalpy (total heat) added is determined by
subtracting the enthalpy of the dry, heated air at Point B from
the enthalpy of the humidified air at Point C as follows:
74.5 kJ/kg – 49.0 kJ/kg = 25.5 kilojoules per
kilogram of dry air
Fig. 18.
The remaining 0.8 kJ/kg is sensible heat. The actual moisture
added per kilogram of dry air is 9.5 grams. The specific volume
of the entering air at Point B is 0.874 cubic meters per kilogram.
For a 4.72 cubic meters per Second system, the weight of the
air passing through is:
4.72 m 3 /s
÷
0.874 m 3 /kg = 5.4 kilograms per
second
The weight of the moisture added is:
5.4 kg/s x 9.5 g/kg = 51.3 grams per second
of moisture
The steam raised the temperature of the air from 32
°
C dry
bulb to 33
°
C dry bulb. To find the latent heat added by the
steam humidifier to the air, determine the enthalpy at Point D
(the enthalpy of the heated air without added moisture) and
subtract it from the enthalpy of the humidified air at Point C.
This is as follows:
74.5 kJ/kg – 49.8 kJ/kg = 24.7 kilojoules per
kilogram of dry air
STEAM
ENTHALPY
2675 kJ/kg
REFERENCE POINT
A 13
°
C DB
LATENT
SENSIBLE
(0.8 kJ/kg)
TOTAL
ENTHALPY
B
C
D 32
°
C DB 33
°
C DB
16 g/kg
6.5 g/kg
50% RH
M15330
49.8
kJ/kg
49
kJ/kg
74.5
kJ/kg
TOTAL HEAT
SENSIBLE HEAT
∆
Hs
∆
Ht
∆
h
∆
W
ENTHALPY
HUMIDITY RATIO
1.0 1.0
0
-
∞ ∞
∞
10.0
5.0
4.0
0.4
0.6
0.8
0.2
3.0
2.5
2.0
1.0
0
-2.0
2.0
4.0
-4.0
-2.0
-1.0
-0.5
-5.0