Theory
A denser fibre packing has more fibre surface per unit volume and therefore a higher resistance to flow. The program estimates the flow resistivity from the bulk density with a power law fitted to measured glass and rock wools (Komatsu, 2008), equation (1); the constants depend on Fibre type. The estimate replaces Flow resistivity in the CFD Darcy term and in the acoustic model.
Equations
| where | meaning | unit |
|---|---|---|
| Estimated flow resistivity | Pa·s/m² | |
| Bulk density (this setting) | kg/m³ | |
| Glass wool 93.8 and 1.420; rock wool 53.1 and 1.571 | - |
Default and rule
- Default
- 30 kg/m³ (shown when the bulk-density estimate is selected)
- Rule
30 kg/m³ is pre-filled when the estimate is selected; enter the density of the actual packing (mass of wool divided by the volume it fills). Example: glass wool at 30 kg/m³ gives Pa·s/m².
- Source
Power-law fit by the program to the measurements in Table 3 of Komatsu (2008). Deviation of the fit from the data: 9.6 % rms / 18.8 % maximum (glass wool), 9.2 % rms / 14.7 % maximum (rock wool).
Valid range > 0; fitted range 20-102.4 kg/m³ (glass wool), 29.7-97 kg/m³ (rock wool)
Values
Above 0.
Extrapolation
Outside the measured densities (glass wool 20-102.4 kg/m³, rock wool 29.7-97 kg/m³) the estimate is an extrapolation, and the field shows a warning.