BAC 3985C - Bleed Rate

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Bleed Line Calculations:Bleedrateisdeterminedbythefollowingformula:
B=E
Where: B=BleedRate(USGPM)
 E=EvaporationRate(USGPM)=Q(USGPM)xR(°F)x0.001
 Q=ProcessFluidFlowRate(USGPM)
 R=Range
 n=NumberofCyclesofConcentration=CR/CM
 CR=ConcentrationinRecirculatingWater
 CM=ConcentrationinMake-upWater
Given:
• 3299CCoolingTower
• ProcessFluidFlowRate=800USGPM
• MaximumAllowableChlorideConcentration=250ppm
• ConcentrationofChloridesinMake-upWater=45ppm
• Range=10°F
Find:BleedRate
Solution:Sointhiscase,
E=Q*R*0.001=800*10*0.001=8USGPM
n=CR=250ppm=5.55
B=E=8USGPM=1.75USGPM
Therefore,inthiscasewemustbleedapproximately1.75USGPMtolimitthe
concentrationofimpurities.

Thisexamplefocusesonasingleparameter(chlorideconcentration)ofwateronly.The
bleedraterequiredforasystem(whenevaluatingmorethanoneparameter)isthehighest
bleedraterequiredtokeepallparameterswithinrecommendedlimits.
NOTE: The evaporation rate (E) can
be determined by any one of the
following methods:
• The evaporation rate is
approximately 2 USGPM per 1
million BTUH of heat rejection.
• The evaporation rate is
approximately 3 USGPM per 100
tons of refrigeration.
• Evaporation Rate =
Q (USGPM) * R * 0.001.
(n-1)
NOTE: Evaporation is proportional
to the load and will vary seasonally.
BAC recommends the use of a
conductivity meter to maximize
water conservation.
CM
45ppm
(n-1) (5.55-1)
Bleed Rate
Bleed Rate