UFC 3-240-13FN
25 May 2005
efficiency and 10 represents very good efficiency. It has been found that the range of 5
to 7 COC represents the most cost-effective situation.
4-2.1.2.1
Calculating COC by Volume. If both makeup and blowdown water
volumes are known, COC by volume can be calculated. The term is defined as:
EQUATION
C=MB
(20)
where
C = COC, no units
M = makeup water, kg/hr (gpm)
B = blowdown losses, kg/hr (gpm)
EXAMPLE:
M = 6.3 liters/sec (100 gpm)
B = 0.63 liters/sec (10 gpm)
C = M B = 10
4-2.1.2.2
Determining COC by Water Analyses. To determine COC, you must
know the mineral content of both makeup and blowdown water. For example, you must
determine both the conductivity of the recirculating cooling tower water and the
conductivity of the makeup water. (Note that the blowdown water will have the same
conductivity as the recirculating water.) Conductivity is commonly measured in
micromhos (mhos). You can also estimate COC by using other water quality
parameters such as chlorides, silica, or sulfates. The relationship is represented by this
equation:
Bmhos
BCl
EQUATION
C = ------ or ------
(21)
Mmhos
MCl
where
C
= COC, no units
Bmhos = conductivity of blowdown (recirculating water), micromhos
(mhos)
Mmhos = conductivity of makeup water, mhos
Cl
= chlorides in blowdown, ppm
Cl
= chlorides in makeup water, ppm
EXAMPLE 4-1:
The measured conductivity of the blowdown (recirculating water) is 800
micromhos and the makeup is 300 micromhos.
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