Size exhaust ducts using reliable engineering relationships. Compare velocity, density, pressure, and flow outputs instantly. Build cleaner designs with graphs, exports, and practical guidance.
| Item | Example Value | Unit |
|---|---|---|
| Duct shape | Round | - |
| Diameter | 0.40 | m |
| Velocity | 12.00 | m/s |
| Gas temperature | 35.00 | °C |
| Absolute pressure | 101.325 | kPa |
| Duct length | 12.00 | m |
| Roughness | 0.15 | mm |
| Volumetric flow result | 1.5080 | m³/s |
| Mass flow result | 1.7274 | kg/s |
| Estimated pressure loss | 43.57 | Pa |
Round duct area: A = πD² / 4
Rectangular duct area: A = W × H
Volumetric flow rate: Q = A × V
Mass flow rate: ṁ = ρ × Q
Hydraulic diameter: Dh = 4A / P, where P is wetted perimeter.
Dynamic pressure: q = 0.5 × ρ × V²
Reynolds number: Re = ρVDh / μ
Darcy pressure loss: ΔP = f × (L / Dh) × (0.5ρV²)
Fan shaft power: Power = Q × ΔP / η
Mach number: M = V / a, where a is gas sound speed.
It estimates exhaust velocity, volumetric flow, mass flow, dynamic pressure, Reynolds number, Mach number, duct friction loss, travel time, air changes, and fan power from one form.
Use velocity mode when duct speed is already known from a design target, balancing report, or equipment requirement and you want the resulting flow rate.
Use mass flow mode when process exhaust is specified by mass discharge, such as heated gas, combustion products, or emissions data, and you need velocity.
Hydraulic diameter lets rectangular ducts use pressure-loss and Reynolds relationships similar to round ducts. It links area and wetted perimeter into one practical flow dimension.
Reynolds number indicates whether the flow is likely laminar or turbulent. That matters because friction factor and pressure loss change strongly with flow regime.
No. It estimates straight-duct friction loss from length, diameter, roughness, and velocity. Bends, dampers, hoods, filters, and transitions should be added separately.
Automatic density uses absolute pressure and temperature for quick engineering estimates. Manual density is useful when gas composition differs from air or has measured properties.
The graph shows how volumetric flow and estimated friction loss move as exhaust velocity changes around the solved condition. It helps visualize operating sensitivity.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.