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Name: Rob Ferguson
Company: French Creek Software
E-mail: frenchcrk@p3.net
WaterCycle: General Tech Support
Date: 18 Mar 1998
Time: 08:39:45
Remote Name: 206.137.135.26
Remote User:
WaterCycle inhibitor models address the conditions you inquired about as follows:
TIME: Time is an integral variable in the calcium carbonate, calcium sulfate and other inhibitor models supplied with WaterCycle. The time dependence of dosage has been verified in the field in systems ranging from highh heat flux, short residence time utility surface condensers, to long holding time (> 72 hours) cooling systems. For example, the HEDP dosage reuired to prevent CaCO3 scale increases about 17X as time goes from 5 to 10 seconds to 24 hours.
EVAPORATION: The most critical parameter to model as water concentrates is the pH. WaterCycle allows you to select the level of accuracy based upon your knowledge of the systems. The simplest (and typically least accurate) metohd for predicting pH is to select the DEFAULT CURVE. This is the pH-Alkalinity curve developed by Dr. Kunz at Air Products from a large sampling of Great Lakes water. The most accurate is to develop your own system dependent model by measuring pH and alkalinity as a water cycles (concentrates) and inputtinng the results into the pH-Alkalinity CURVE module. Then select USER DEFINED curve. A quick way to improve accuracy is the "one point" curve. Enter one point into the pH-Alkalinity table. WaterCycle will use the slope of the Kunz (default) curve and translate the intercept to the actual point enetered. IMPORTANT NOTE: Use a concentrated water pH-alkalinity NOT A SOURCE WATER.
pH IMPACT ON INHIBITORS: The Laboratory Edition of WaterCycle allows you to include pH as a variable and model the impact of pH on the dissociation state of inhibitor functional groups. This is typically not critical in cooling water systems but can be of importance in systems operating near the inhibitor pKa's.
HEAT FLUX: High heat flux systems typically have a much higher film temperature than low flux systems. The selection of the Temperature for a dosage recommendation is the most ipmortant parameter in modelling systems under heat transfer. WaterCycle has been used successfully to model utility surface condensers (use outlet temperature + 5 to 10 degrees F), through overhead condensers. Don't forget to look at silica species at the lower temperature you anticipate. The Temperature and pH profiles provide an excellent means of determining the impact of a dosage calculated at too low a temperature or pH.
Please fell free to ask further questions conerning the models.
Rob