1. EVAPORATION LOSS
This is the desired and essential process that makes cooling towers work.
- What it is: The conversion of a small portion of the circulating water from liquid to vapor (evaporation). This phase change absorbs latent heat of vaporization (~1000 BTU/lb), which is the primary driver of cooling.
- Cause: When warm water is exposed to unsaturated air, the most energetic water molecules escape the liquid surface.
- Key Characteristics:
- Invisible: You cannot see pure water vapor.
- Unavoidable for Cooling: The amount is determined by heat load and atmospheric conditions.
- Formula (Approximate):
Evaporation Loss (GPM) ≈ Circulation Rate (GPM) × Range (°F) / 1000
*(More precise: E (GPM) = Flow × Range × 0.00085)*
- Example: A tower cooling 1000 GPM by a 10°F Range has ~10 GPM of evaporation loss.
- Impact on System: Evaporation is why Cycles of Concentration (COC) increases. As pure water leaves as vapor, minerals/salts remain behind, concentrating the remaining water. This necessitates Blow down for control.