1. COOLING
TOWER
By. Engr. Yuri G. Melliza

2. B Air Out
hB,WB, ma
Hot water 1
m1
t1
h1
Fan
A Air in
t3, h3, m3
hA,WA, ma
Make-up water 3
Cold water 2
t 2, h 2, m 2 Catch Basin

3. Cooling Tower
A Cooling tower is a wind braced enclosure or
shell usually made of wood, concrete or metal
with fillings on the inside to aid water exposure.
The water to be cooled is pumped into a
distributing header at the top of the tower from
which it drops in sprays to the filling. The water
spreads out in the filling thus exposing new
water surfaces to the air circulating through the
tower. The cooled water drops to the bottom of
the tower called the catch basin. The air
circulating through the tower becomes partially
saturated with moisture by evaporating some

4. Fundamental Equations:
1. Actual Cooling Range (ACR)
ACR = t1 - t2
2. Cooling Tower Approach (A)
A = t2 - tWA
3. Theoretical Cooling Range (TCR)
TCR = t1 – tWA
4. Cooling Tower Efficiency
t1 − t 2
e= x 100%
t 1 − t WA

5. Vapor Pressure
PV = PW - PA(td - tW)
here: A = 6.66 x 10-4 (For tW of equal or greater
than 0°C.
A = 5.94 x 10-4 (For tW of less than 0°
Specific Humidity or Humidity Ratio
0.622 Pv kgm
W=
P − Pv kgda
7. Relative Humidity
Pv
Φ= x 100 %
Pd

6. 8. Enthalpy
h = 1.0045td + W(2501.3 + 1.86td) KJ/kgda
9. Specific Volume
0.287(t d + 273) m 3
υ=
(P − Pv) kgda
10. Degree of Saturation
 P − Pd 
μ = Φ 
 P − Pv 

7. 11. By moisture balance in the tower:
a) With make up water, m1 = m2
m3 = ma(WB - WA) kg/sec
b) Without make up water available,
m1 ≠ m2:
12. By Energy Balance in the (W - W )
m1 - m2 = ma tower
B A
a. Considering make up water
kg/sec
m1 (h1 − h2 )
ma = kg/sec
(hB − hA ) − (WB − WA )h3
m1h1 − ma [ (hB − hA ) − (WB − WA )h3 ]
h2 = KJ/kg
m1

8. b. Without considering make up water
m1 (h1 − h 2 )
ma = kg/sec
(h B − h A ) − (WB − WA )h 2
m1h1 − m a (h B − h A )
h2 = KJ/kg
m1 − m a (WB − WA )
13. Driving Pressure
gH( ρ o - ρ i )
ΔPd = KPa
1000

9. 14. Mass Flow rate of air and vapor mixture
m = ma(1+W) kg/sec
m = ma + mv
15. Cooling water flow rate related to Brake
Power
of an Engine Brake Power
m w = 904.3 L/hr
t1 - t 2

10. where:
m1 - mass flow rate of water entering
tower in kg/sec
m2 - mass flow rate of cooled water in
kg/sec
m3 - make up water in kg/sec
h1 - enthalpy of hot water in KJ/kg
h2 - enthalpy of cooled water in KJ/kg
h3 - enthalpy of make up water in
KJ/kg t1 - temperature of hot water, °C
hA - enthalpy of air entering tower in t2 - temperature of cooled water, °C
KJ/kgda t3 - temperature of make up water, °C
hB - enthalpy of air leaving tower in H - tower height, meters
KJ/kgda ρo - density of outside air and vapor mixture
WA - humidity ratio of air entering kg/m3
tower in kgm/kgda ρi - density of inside air and vapor mixture,
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