The Blueprint of Water

Suspended Solids: Problem Set

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⟵ 10 Suspended Solids (Engineering Notes) · Contents · 10 Suspended Solids (Answer Key) ⟶

Suspended Solids: 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

  1. Explain in one sentence why dissolved solids go wherever the water goes, but suspended solids go wherever the system lets them. What physical principle governs each?

  2. A cooling tower has excellent water chemistry - inhibitor residuals on target, biocide fed on schedule, pH and conductivity within range - but corrosion coupons show aggressive pitting. The basin has 3 inches of settled silt. Explain how these two observations are consistent.

  3. Starting with a single event - a windstorm deposits a heavy layer of dust in a cooling tower basin - describe the sequence of consequences through all three pillars (corrosion, biology, scale) if the solids are not removed.

  4. A closed chilled water loop shows brown, turbid water at 45 NTU despite having been in operation for two years. Is this a suspended solids problem or something else? What would you investigate first?

Level 2: Applied Thinking

  1. A cooling tower has a system volume of 3,000 gallons and a recirculation rate of 800 GPM. (a) What sidestream flow rate is needed to turn over the system volume every 4 hours? (b) What percentage of the recirculation rate is this? (c) If the tower is near an active construction site, would you recommend increasing this target?

  2. Using the concept from Stokes’ Law, explain why a hydrocyclone separator is effective for removing rust particles (density ~5,200 kg/m³, diameter ~50 µm) but ineffective for biological debris (density ~1,050 kg/m³, diameter ~20 µm). You do not need to calculate - explain the reasoning.

  3. Your corrosion coupon program shows carbon steel rates of 1.2 MPY - within the “good” range. But during a shutdown, you find deep pitting beneath silt deposits on horizontal pipe runs. Explain why the coupons missed this, and propose a change to the monitoring program.

Level 3: System Integration

  1. A 1,000-ton chiller system operates 4,000 hours per year at 8,000 installed. If it restores the condenser to clean conditions within one cooling season, what is the simple payback period?

  2. A water treater increases the dispersant dose in a heavily fouled cooling tower. Within 48 hours, turbidity increases from 20 to 60 NTU and condenser approach temperature actually improves by 1°F. Explain what is happening and whether this is a problem or a success.

  3. You are called to a cooling tower that has not had sidestream filtration, has been running without consistent biocide treatment, and has visible silt deposits in the basin. The customer wants you to “fix the chemistry.” Write a brief explanation (4–6 sentences) of why adjusting chemical feed rates alone will not solve this problem. Reference at least two amplification pathways.

Problem notes

Each problem as its own linked note.

10.1 · 10.2 · 10.3 · 10.4 · 10.5 · 10.6 · 10.7 · 10.8 · 10.9 · 10.10

⟵ 10 Suspended Solids (Engineering Notes) · Contents · 10 Suspended Solids (Answer Key) ⟶

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