Evaporation Loss vs. Drift Loss: Fundamental Differences
Both are forms of water loss in a cooling tower, but they differ fundamentally in mechanism, purpose, controllability, and impact.
| Evaporation Loss vs. Drift Loss: Fundamental Differences Both are forms of water loss in a cooling tower, but they differ fundamentally in mechanism, purpose, controllability, and impact. Quick Comparison Table Aspect Evaporation Loss Drift Loss Nature Intentional & Functional – The core cooling mechanism. Unintentional & Parasitic – A system inefficiency. Mechanism Phase change: Liquid water → Water vapor (molecules enter air). Physical entrainment: Liquid droplets → Carried away by air stream. State of Water Invisible vapor (gas). Visible liquid droplets (mist). Purpose Primary purpose of the tower. Responsible for ~80% of heat rejection. No beneficial purpose. Pure water and energy waste. Controllability Directly proportional to cooling load. Cannot be eliminated without shutting down cooling. Can be minimized (not eliminated) with efficient drift eliminators. Typical Magnitude Large: ~1-2% of total circulating flow rate for every 10°F Range. Very Small: 0.001% – 0.2% of circulating flow (modern towers: 0.001%-0.005%). Impact on Water Chemistry Concentrates dissolved solids (increases Cycles of Concentration). Dilutes nothing; removes treated water at system concentration. |