Roughness & Surface Coefficients of Ventilation Ducts
Surface coefficients to calculate friction and major pressure loss in ventilation ducts - concrete, galvanized steel, corroded steel and more
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For turbulent flow the friction coefficient depends on the Reynolds Number and the roughness of the duct or pipe wall. Relative roughness for materials are determined by experiments. Relative roughness for some common materials can be found in the table below
| Surface | Roughness Coefficients- k | |
| x 10-3 m | feet | |
| Copper, Lead, Brass, Aluminum (new) | 0.001 - 0.002 | 3.33 - 6.7 10-6 |
| PVC and Plastic Pipes | 0.0015 - 0.007 | 0.5 - 2.33 10-5 |
| Stainless steel | 0.015 | 5 10-5 |
| Steel commercial pipe | 0.045 - 0.09 | 1.5 - 3 10-4 |
| Stretched steel | 0.015 | 5 10-5 |
| Weld steel | 0.045 | 1.5 10-4 |
| Galvanized steel | 0.15 | 5 10-4 |
| Rusted steel (corrosion) | 0.15 - 4 | 5 - 133 10-4 |
| New cast iron | 0.25 - 0.8 | 8 - 27 10-4 |
| Worn cast iron | 0.8 - 1.5 | 2.7 - 5 10-3 |
| Rusty cast iron | 1.5 - 2.5 | 5 - 8.3 10-3 |
| Sheet or asphalted cast iron | 0.01 - 0.015 | 3.33 - 5 10-5 |
| Smoothed cement | 0.3 | 1 10-3 |
| Ordinary concrete | 0.3 - 1 | 1 - 3.33 10-3 |
| Coarse concrete | 0.3 - 5 | 1 - 16.7 10-3 |
| Well planed wood | 0.18 - 0,9 | 6 - 30 10-4 |
| Ordinary wood | 5 | 16.7 10-3 |
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