Stack Plume Rise Calculator

How it is calculated

The tool uses Holland's plume rise equation: ΔH = (Vs × d ÷ u) × (1.5 + 2.68×10⁻³ × P × d × (Ts − Ta) ÷ Ts). Vs is the stack exit velocity in m/s, d the inner stack diameter in m, u the wind speed in m/s, P the atmospheric pressure in millibars (about 1013 at sea level), and Ts and Ta the stack gas and ambient air temperatures in kelvin. The first factor is the momentum term and the bracket adds buoyancy, which grows with the temperature excess. The result is the rise in metres above the stack top, to two decimals. Wind speed and Ts must be above zero. The tool has no stability correction, and if Ts is below Ta the buoyancy term turns negative and the rise can go below zero, which is not physical.

Common mistakes

• Entering Ts and Ta in °C; the temperature ratio needs kelvin, so 147 °C must be entered as 420 K.
• Giving the pressure in kPa, for example 101.3 (1 kPa = 10 mbar); the equation expects millibars, and 101.3 drops the same stack's rise from 19.24 m to 10.02 m.
• Treating the result as the total plume height; it is only the rise above the stack top, so the stack height must be added for the effective height.
• Using ambient temperature above the gas temperature, which gives a smaller rise or even a negative one.
• Entering the wind speed measured at ground level or in km/h rather than m/s at stack height; the rise is inversely proportional to the wind speed.