Enter plume and stack inputs
Example data table
This sample table shows how different operating conditions can change plume rise and effective stack height.
| Scenario | Stack height (m) | Diameter (m) | Exit velocity (m/s) | Gas temp (°C) | Ambient (°C) | Wind (m/s) | Class | Distance (m) | Rise (m) | Effective height (m) |
|---|---|---|---|---|---|---|---|---|---|---|
| Power plant stack | 80 | 3.0 | 20 | 160 | 24 | 6.0 | D | 1200 | 97.50 | 177.50 |
| Process heater vent | 45 | 1.5 | 24 | 190 | 28 | 4.5 | C | 800 | 24.00 | 69.00 |
| Boiler stack near building | 55 | 2.0 | 16 | 135 | 22 | 7.5 | E | 1000 | 14.70 | 69.70 |
Formula used
This calculator uses Briggs-style screening equations for plume rise. The model compares buoyancy-driven and momentum-driven behavior, then reports the dominant result or a user-selected path.
Buoyancy flux, F = g × Vs × d² × (Ts - Ta) / (4 × Ts)
Momentum parameter, M = Vs² × d² × (Ta / Ts) / 4
Neutral or unstable final buoyancy rise = 21.4 × F^0.75 / u
Stable final buoyancy rise = 2.6 × (F / (u × s))^(1/3)
Momentum rise = 3 × d × Vs / u
Effective stack height = physical stack height + plume rise
The distance-based rise uses a capped screening estimate. Stable classes can also use an optional custom s parameter. A simple building check reduces rise when the stack does not clear a basic 2.5 times building height screening ratio.
How to use this calculator
Enter the physical stack height, diameter, gas exit velocity, and stack gas temperature. Add ambient temperature and the wind speed measured or estimated near stack height.
Select the Pasquill stability class that best matches site conditions. Use the custom stability parameter only when you already have a project-specific value.
Provide the downwind distance where you want a screening estimate. Add nearby building height when structure-induced turbulence may matter.
Click the calculate button to view plume rise at the selected distance, final rise, effective stack height, buoyancy and momentum parameters, and screening notes.
Use the export buttons after calculation to save a CSV summary or a PDF report for design review, preliminary air modeling files, or internal documentation.
Frequently asked questions
1. What does plume rise mean?
Plume rise is the vertical lift of an exhaust stream above the physical stack top. It comes from thermal buoyancy, exit momentum, and local atmospheric conditions.
2. Why does wind speed matter so much?
Higher wind speed usually suppresses plume rise because it bends and dilutes the jet faster. Lower wind allows the plume to keep rising longer.
3. When should I use buoyancy mode?
Use buoyancy mode when the gas is much hotter than ambient air and thermal lift clearly dominates. Auto mode already checks that relationship for screening work.
4. When should I use momentum mode?
Use momentum mode when exit velocity is very strong relative to wind speed and temperature difference is modest. This often applies to energetic vents or fast exhaust nozzles.
5. What is the stability class?
The stability class describes atmospheric turbulence and mixing. Unstable classes encourage vertical motion, while stable classes suppress it and usually lower plume rise.
6. Does this replace a full dispersion model?
No. This is a screening tool for quick engineering estimates. Regulatory studies often require a full dispersion model, approved meteorology, terrain treatment, and source characterization.
7. Why is there a building height input?
Nearby structures can disturb flow and reduce effective plume rise. The calculator applies a simple screening penalty when the stack is too short relative to the building.
8. Can I export the results?
Yes. After calculation, use the CSV button for spreadsheet-friendly output or the PDF button for a report-style file you can share or archive.