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Cooling Tower Make-up Water |
Cooling Tower Make-up Water Flow Rate Calculation
Rate of evaporation is approximately 1% of the circulation flow for each 10 °F (5.56 °C) of rise between the outlet and inlet across the tower. A correction is needed for factors such as wind, relative humidity, etc. Factor of 0.85 works out to be a reasonable approximation. If the climate is particularly moist, value may go down to 0.65; it if is very dry, it may go upto 1.0 - 1.2.
To calculate the make-up water flow rate, determine the evaporation rate using one of the following:
1. The evaporation rate is approximately 2 GPM per 1 million BTU/Hr of heat rejection.
2. The evaporation rate is approximately 3 GPM per 100 tons of refrigeration.
3. Evaporation Rate (GPM) = Water Flow Rate (GPM) x Range (°F) x 0.001.
Multiply the evaporation rate by the appropriate correction factor in the table below to calculate the make-up water flow rate, in GPM.
|
Cycles of Concentration |
Correction Factor |
|
2 |
2.00 |
|
3 |
1.50 |
|
4 |
1.33 |
|
5 |
1.25 |
|
6 |
1.20 |
|
7 |
1.17 |
|
8 |
1.14 |
|
9 |
1.13 |
|
10 |
1.11 |
Drift is entrained water in the tower discharge vapors. Drift loss varies between 0.1 and 0.2 % of Circulation flow. It can be as low as 0.01 % of circulation flow, if the cooling tower has windage drift eliminators.
Blowdown discards a portion of the concentrated circulating water due to the evaporation process in order to lower the system solids concentration. Blowdown can be calculated according to number of cycles of concentration required to limit scale formation.
https://checalc.com/solved/ctmakeup.html