Which of the following would provide good scale prevention in an open water cooled system such as a cooling tower or evaporator condenser?

• A. Calcium carbonate deposit
• B. Sodium chloride solution
• C. A sulfuric acid chromate solution
• D. Pure water

Answer: (C)

In open cooling systems, minerals dissolved in the make-up water can precipitate as scale on heat-transfer surfaces when water is heated and concentrated. To prevent this, chemical treatments that keep hardness salts in solution and protect surfaces are used. A sulfuric acid chromate solution does both: the sulfuric acid lowers pH, increasing the solubility of calcium carbonate and similar scale-forming compounds, while the chromate component provides corrosion protection and helps form a protective film on metal. This combination reduces scale formation and protects equipment, making it an effective scale preventive. The other options either introduce or leave minerals that can form scale (calcium carbonate), promote conditions that don’t prevent scaling (sodium chloride), or rely on pure water without inhibitors, which isn’t reliable for preventing scale in practice.