The bleed rate of an evaporative cooling tower is adjusted to maintain which parameter?

• A. Return water temperature
• B. Water seal in the drain line trap
• C. The desired leaving water temperature
• D. The desired concentration of total dissolved solids

Answer: (D)

Bleed rate is used to control the concentration of dissolved minerals in the circulating water. As water evaporates in an evaporative cooling tower, minerals are left behind, causing total dissolved solids (TDS) to rise. If TDS gets too high, scaling, corrosion, and efficiency losses can occur. By bleeding off a portion of the circulating water and replacing it with fresh make-up water, you remove concentrated water and keep the TDS (or the related conductivity) at a target level. This keeps the water chemistry in the proper range and maintains tower performance.

Other factors like return water temperature or leaving water temperature aren’t directly controlled by bleed rate, and the drain trap’s water seal is a separate plumbing consideration.