![]() ![]() He determined that it was most accurate when the cooling water values were in the following ranges: He found the PSI method provided the most accurate values of the three methods. The best review of the LSI, RSI and PSI methods was made independently by Cavano in an article published in The Analyst magazine in the fall of 1999. The WC modifies the pHs value as influenced by the common ion effect. The maximum water temperature (as Fahrenheit or Celsius) occurring in the cooling water system.The total alkalinity (as CaCO 3) value.The total dissolved solids or conductivity value. The pHs is the pH of saturation of calcium carbonate, and it is used by all the indices. Table 1 provides an overview of the major indices used to predict calcium carbonate scaling. I will thus only be addressing the accuracy of predicting calcium carbonate scale in cooling water systems. The WC program also calculates other scales, depending upon the water constituents. It is important to be clear on one point: All of these indices were developed only to predict calcium carbonate scaling tendencies. However, we will compare the most commonly used indices -the LSI, RSI, PSI and WC methods - with regard to how well they relate and their accuracy to actual field cooling waters. This article will not attempt to compare all of these methods for predicting calcium carbonate scaling tendencies of cooling water. These were not major improvements and thus have not been extensively adopted. Numerous articles appeared during the next 12 years to promulgate modifications to the LSI and RSI indices to improve scale predictions versus actual scaling waters. Since this index is primarily for cooling waters, both end users and water treatment companies have adopted it. The name was changed to the practical scaling index and later to the Puckorius scaling index (PSI) in a 1983 Power magazine article. It was dubbed the modified stability index (MSI) when introduced in a paper published by Brooke and Puckorius. It was not until 1983 that a new method was developed primarily for cooling waters. Other methods also were developed, mainly for potable water, but they were not used much. It now is being used mainly for cooling water even though it was not modified in any way that I am aware of for use in this application. Known as the Ryznar stability index (RSI), this test was developed primarily for predicting the calcium carbonate scale tendency of potable water. Several other predictive methods were later developed. ![]()
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