COOLING WATER SYSTEM TERMINOLOGY
Alkalinity Measure of bicarbonates, carbonates and hydroxides
in water usually expressed as equivalent concentration of CaCo3. It is measured by titration with standard
acid using methyl orange and phenolphthalein indicators and hence called as P/M
Alkalinity.
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Test Results
|
Concentration of |
||
|
Hydroxide
|
Carbonate
|
Bicarbonate
|
|
P = 0 |
0
|
0
|
M
|
|
P <
½ M
|
0
|
2P
|
M-2P
|
|
P = ½
M
|
0
|
2P |
0
|
|
P >
½ M
|
2P- M
|
2 (M-P)
|
0
|
|
P = M
|
M
|
0
|
0
|
Approach Difference
between temperature of cold water leaving tower and the ambient wet bulb
temperature
Basin Reservoir
underlying the cooling towers to receive the cold water from the tower and
direct its flow to the suction line or sump.
Blowdown (Bleed off) The
water continuously or intermittently purged from the system to remove sluge and
keep the dissolved solids at a tolerable concentration. It may be intentionally purged or may be
accidentally lost through leaks or through drift. The addition of treatment chemicals is based
on blowdown.
Circulation Rate The
amount of hot water flowing into the tower or cold water flowing from the sump
to the system usually expressed as volume per hour.
Cooling Range Difference
between the hot water temperature returning to cooling tower and the cold water
temperature leaving the cooling tower.
Cycles of concentration A measure of the degree to which dissolved solids are being
concentrated in circulating water due to recirculation or recycling of
water. Measured as ratio of ‘X’ ppm of
soluble and measurable constituent present in circulating water to ‘Y’ ppm of
same constituent in make up water.
The constituent should be unaffected by treatment or
operating conditions in circulation water
Distribution Basin (deck) Shallow pan type elevated basin used for distribution of hot water over the tower filling
Drift (windage,
carryover) Water loss from the tower
as liquid droplets entrained in exhaust air usually expressed as percentage of
circulation rate (0.1 to 0.2 %)
Evaporation Rate The
rate at which the water is being evaporated to cool the circulating water. It is around 0.18 % of circulation rate per
degree centigrade of cooling range
Exhaust air The
mixture of air and its associated water vapour leaving the tower.
Fill Deck The
assembly of splash bars comprising the tower filling. These usually interrupt the downword fall of
water at regular intervals forming splash of water that cause water to form
smaller droplets to provide air-water contact.
Hardness Measure
of calcium and magnesium ion content of water normally expressed as equivalent
of CaCO3. Temporary hardness is due to
presence of bicarbonates, carbonates and hydroxides of Ca and Mg also known as
carbonate hardness while permanent hardness is due to chlorides and sulfates of
Ca and Mg also known as non carbonate hardness.
Heat Load Heat
removed from the circulating water within the tower expressed as calories or
B.t.u per unit time. It can be
calculated from the cooling range and circulation rate.
Heat load Kcal/Hr = Circulation Rate (lit/ min) X 60 X
Cooling Range (0C)
Hold Up Total
quantity of water in the system including basin, sump & pipelines.
Louver Members
installed horizontally in a tower wall to provide openings through which air
enters the tower usually installed at an angle to the direction of airflow to
the tower.
Make up Water
added to the circulating water system to replace water lost from the system by
evaporation, drift, bleed off and leakage to maintain the quantity of water in
the system.
Retention Time The
time required for water to fall from the distribution header to cooling tower
basin.
Spray Nozzle Used
in a pressure distribution system to break up the flow of circulating water
into droplets and effect uniform spreading of the water.
ESTIMATION OF CORROSION RATE BY COUPON
METHOD
Weight Loss (mg) X
1.437
CORROSION RATE (mpy) =
Area in dm2 X Exposure in no. of days X
density
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