The amount of water entering the system must be equal to the amount leaving the system.īD = Blowdown Rate. Water that must be added to replace water lost from the recirculating system by evaporation and bleed-off (or blowdown) is called makeup water (MU). These sources include chlorination, chemical additives, process leaks, acid additions, and airborne gases. (There may also be scale forming in the heat transfer equipment, thereby impeding production.) Entry of ions from sources other than the makeup water can invalidate any ratio being developed. If the cycles of calcium concentration are consistently lower than the cycles of magnesium concentration, for example, the calcium can be assumed to be precipitating in the system. Repeating this same testing for scaling species (e.g., calcium) will provide an indication if scaling is occurring or if the system is in chemical balance. Compare its concentration in the makeup water to its concentration in the recirculating water by dividing the tower content by the makeup content. To check the concentration ratio in a system, select and monitor a soluble ion (such as silica or magnesium) that is present in sufficient quantity, stable, and easily tested. The rate at which water is bled from a system (in gpm m3/hr) compared with the amount of fresh water being introduced in the system (in gpm m3/hr) will also determine the concentration ratio. Most systems cannot tolerate any scale therefore, the level or concentration of critical scaling-prone ions in the water is usually controlled by a combination of bleeding off a certain portion of the recirculation water and adding anti-scaling compounds. If the only system water loss was through evaporation, the dissolved ions in the recirculating water would continue to concentrate (from the ions left after evaporation) until the solubility of each ion in the water was exceeded and massive scale/deposition resulted. All of the dissolved ions are left behind to concentrate in the system. Theoretically, evaporation from a cooling tower is pure water. Concentration ratio is also referred to as the cycles of concentration.Ĭ R = Specific Ion Concentration in the Recirculation Water Specific Ion
The concentration ratio of an ion carried in a recirculating system is merely the concentration of that ion in the recirculating water divided by the concentration of the ion in the makeup water.
Many times throttling valves, pipe restrictions, and head pressure restrictions interfere and can produce deviations as great as 50-75% from the name plate values.Ĭheck out our cooling tower conductivity controller, just click here!Ĭoncentration Ratio or Cycles of Concentration It can be grossly misleading to simply use the pump name plate data to determine recirculating rate.
COOLING TOWER DESIGN CALCULATION SOFTWARE HOW TO
A detailed description of how to determine recirculating rate is given in the PAC-3 section of the Value Added Troubleshooting Guide. The recirculation rate can be determined from information on pump performance, tower hydraulics, etc. To maintain a flow of water through the heat transfer equipment, water must be pumped or recirculated.
This difference can be used to calculate the approximate amount of evaporation that has occurred in the cooling tower: The temperature drop ( ∆T ) for a cooling tower can be measured by taking the temperature of the tower return water (TR) and subtracting the temperature of the basin supply water (TS). Details for calculating evaporation rate based upon temperature and humidity conditions are provided in the PAC-3 section of the Value Added Troubleshooting Guide. This figure can be used for estimating purposes, but should not be used when more exact information is required (e.g., in a proposal, problem solving, etc.).
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