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Cooling Tower Plume Calculator Engineering & Industrial
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Cooling Tower Plume Calculator

Determine visible fog plume occurrence, psychrometric supersaturation risk, and required dry hybrid heating coil capacity (MBH) to eliminate visible emissions.

Plume Formation Status
Dense Visible Fog
High Supersaturation (Psychrometric fog line crossed)
Dry Coil Heat Required
2,850 MBH
835 kW sensible heat
Exhaust Reheat ΔT
+22.0°F
Lowers exhaust RH to 52%
Condensed Water in Plume: 3.4 lb water / min
Plume Abated Discharge Temp: 112.0°F dry bulb
Regulatory Sensitivity: Airport Runway / Highway Hazard
Cold humid ambient air creates intense fogging unless dry finned hybrid reheat coils are engaged.

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Cooling Tower Plume Physics & Psychrometric Abatement

Cooling tower plumes consist of pure water droplets formed when warm, saturated exhaust air leaves the cooling tower and mixes with colder ambient air. Even though both air streams may be unsaturated, the nonlinear shape of the psychrometric saturation curve causes the straight mixing line to cross into the supersaturated fog region, causing moisture to condense into a thick, visible cloud.

Hybrid Plume Abatement Operation

  1. Dry Section Sensible Heating:
    A hybrid wet/dry cooling tower routes warm circulating water through dry finned-tube coils positioned above the drift eliminators, sensibly heating the saturated wet exhaust air without adding moisture.
  2. Lowering Discharge Humidity:
    Heating the exhaust air lowers its relative humidity and shifts the psychrometric discharge state away from the 100% saturation curve so the mixing line with ambient air never enters the supersaturated fog zone.
  3. Sensible Reheat Equation:
    Q_reheat (BTU/hr) = 1.08 × CFM × ΔT_reheat

Frequently Asked Questions

Why do cooling towers generate visible vapor plumes in cold weather?

When warm, 100% saturated air from inside the cooling tower mixes with cold ambient air, the nonlinear psychrometric saturation curve causes the mixed air to become supersaturated, condensing into visible water droplets (fog).

How does a hybrid wet/dry cooling tower eliminate plumes?

Hybrid towers route hot water through dry finned cooling coils above the wet fill, sensibly heating the saturated air to reduce its relative humidity so the mixture with outdoor air never enters the condensation region.

Is a cooling tower plume harmful smoke or air pollution?

No. Cooling tower plumes consist entirely of clean, condensed water vapor identical to natural morning clouds or steam rising from a hot beverage.