⟵ 08 Scale (Engineering Notes) · Contents · 08 Scale (Answer Key) ⟶
Scale: Problem Set
“These are only provided to reinforce understanding. The Engineering Notes contain some of the information that will be required. Make sure to employ dimensional analysis for all unit conversions.”
Level 1: Conceptual Mastery
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A tower is running at LSI = +1.1 but has no visible scaling. Give two operational reasons this can be true.
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Explain why CaCO₃ often precipitates on heat-transfer surfaces even when the bulk water looks stable.
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Define supersaturation in one sentence. Then explain why supersaturated water can remain clear for weeks.
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Explain how a phosphate-based inhibitor can itself become a source of scale. Name the scaling salt involved.
Level 2: Applied Thinking
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A water treater says, “Our LSI is negative, so we don’t have a scale problem.” The makeup water contains 80 mg/L silica and the tower is running at 5 cycles. Why might the treater be wrong?
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Makeup conductivity = 850 µS/cm; tower conductivity = 3,400 µS/cm. Estimate cycles of concentration.
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A tower uses sulfuric acid for pH control. Makeup sulfate = 50 mg/L. At 6 cycles, tower sulfate is measured at 480 mg/L - significantly higher than 50 × 6 = 300 mg/L. Why is the measured value higher than predicted?
Level 3: System Integration
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Compute pHₛ and LSI for: pH = 8.6, T = 40°C, TDS = 2,200 mg/L, Ca hardness = 320 mg/L as CaCO₃, M-alkalinity = 220 mg/L as CaCO₃. Round logs to 2 decimals.
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Using pHₛ from Question 8, compute RSI and interpret.
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Using alkalinity from Question 8, compute pHeq and PSI. Interpret.
Problem notes
Each problem as its own linked note.
8.1 · 8.2 · 8.3 · 8.4 · 8.5 · 8.6 · 8.7 · 8.8 · 8.9 · 8.10
⟵ 08 Scale (Engineering Notes) · Contents · 08 Scale (Answer Key) ⟶