Airflow resistance measurement of fibrous materials at high temperatures for acoustical applications

Abstract

For some industrial applications it is necessary to assess the acoustic properties of porous materials at high temperatures; hence, airflow resistance measurements on fibrous materials have been carried out at temperatures up to 800 °C. A comparison of a high temperature test rig and a test rig satisfying the requirements of ISO 9053-1 indicated no significant difference between the two rigs at room temperature. For measurements in the high temperature test rig at and above 600 °C there were changes in the sample thickness that could be linked to the onset of crystallisation. This meant that regression analysis had to establish relationships between the sample mass (rather than bulk density) and the specific airflow resistance (rather than airflow resistivity). Power law regression for AES, basalt wool and rock wool show that, on average, the specific airflow resistance is proportional to T0.7 (where T is the absolute temperature in Kelvin) at temperatures where there has been no reduction in sample thickness or other material change due to temperature. For fibrous materials, these results provide more evidence that the temperature-dependence is mainly determined by the air viscosity. Measurements on AES at 20 °C indicate negligible change in the specific airflow resistance when measured with flow velocities between 0.5 × 10−3 and 1.83 × 10−3 m/s but significant differences at 800 °C.