Graduate Thesis Or Dissertation
 

Effects of water quality and surface temperature on the scaling characteristics of cooling tower water

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  • The fouling of cooling tower water was investigated as a function of heater surface temperature and water quality. In particular, the effects on fouling of the addition of calcium in excess of the amounts required for saturation were examined. First, the average bulk water temperature was 97 ± 1 degree F, water velocities ranged from 3 to 8ft/s, heated surface temperatures varied from 105 to 165 degrees F, and the average effective calcium hardness ranged from 560 to 780 ppm as CaCO₃. Additionally, the effects of pH in the range 7 to 9 were observed for water with lower levels of calcium. For these runs, the average bulk water temperature ranged from 97 to 106 degrees F. Water velocities of 3 and 5 ft/s were used, and the surface temperatures were in the range 155 to 5 ft/s were used:and the surface temperatures were in the range 155 to 185 degrees F. The average measured calcium hardness varied from 290 to 400 ppm as CaCO₃. Of the runs with excess calcium, only one had significant fouling, suggesting fouling was suppressed. From the pH runs it appears that there is a minimum in the fouling tendency at a pH near 8. For the runs for which the deposits were not primarily CaCO₃, the surface temperature effects on the asymptotic fouling resistance to heat transfer corresponded well with predictions in the literature. For deposits which were almost pure calcium carbonate, no temperature dependence of the fouling factor could be shown. The material deposited was found to correspond strongly with the Ryznar stability index, with each material deposited in a unique, limited range of the index.
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