Cooling-Tower Visible-Plume Predictor

What this predictor does

Warm tower exhaust is mixed with ambient air in small steps. At each step, the tool conserves moist-air enthalpy and humidity ratio, then compares the mixed state with the saturation humidity ratio. A visible condensation plume is thermodynamically possible wherever the mixing path lies above saturation.

Inputs

Example conditions

Ambient dry-bulb temperature °C

Outdoor air temperature near the tower discharge.

Ambient relative humidity %

Use a concurrent value, not a seasonal average.

Tower exhaust temperature °C

Air temperature at the fan stack or tower outlet.

Tower exhaust relative humidity %

Wet-tower exhaust is often near saturation. Use measured or vendor data where available.

Atmospheric pressure kPa

Pressure affects humidity ratio. Sea-level standard pressure is 101.325 kPa.

Results

THERMODYNAMIC PLUME POTENTIAL YES

Strong visible-plume potential A substantial part of the ideal mixing path is supersaturated.

Plume-potential scaleStrong

None

Marginal

Moderate

Strong

Maximum condensate potential: 1.02 g/kg dry airScreening scale — not measured opacity or plume length

Screening class

Strong

Based on peak supersaturation

Maximum mixed-air RH

118.2%

Before condensate removal

Maximum condensate potential

1.02 g/kg

Per kg of dry mixed air

Peak mixture temperature

12.4 °C

At maximum supersaturation

Condensation mixing range

8–92%

Exhaust fraction by dry-air mass

Ambient dew point

−2.0 °C

Moisture context

Psychrometric mixing path

The saturation curve is the maximum water-vapour content of air at each temperature. The red portion of the mixing path is above saturation and represents theoretical condensate formation.

Saturation boundaryUnsaturated mixingCondensation zone

Scroll the plot horizontally for readable labels.

How to reduce visible plume

01

Use a dry or hybrid section

Heating or drying the discharge lowers its relative humidity and can keep the mixing path below saturation.

02

Mix in dry air before discharge

Plume-abatement systems blend warm dry air with saturated wet-section exhaust before it reaches the atmosphere.

03

Check concurrent winter conditions

Low ambient temperature and high relative humidity are typically the most plume-prone combination. Use site weather bins, not annual averages.

04

Escalate when impacts matter

For roads, airports, buildings or electrical equipment, use a site-specific dispersion/CFD study that addresses plume rise, recirculation, icing and ground contact.

Interpretation and limitations

Visible plume is not the same as drift. A visible plume is mainly condensed water vapour. Drift consists of liquid droplets carried out of the tower and may contain dissolved cooling-water constituents.

The predictor answers one question only: can ideal mixing cause supersaturation? A positive result does not mean a long or ground-level plume will occur. Wind speed, turbulence, exit velocity, tower geometry, ambient stability, droplet nuclei and sunlight all affect observed visibility.