| Popis: |
Among all the transient techniques of measurement of the thermal conductivity, the hot-wire method is an interesting alternative to the standard guarded hot-plate method. However, it has been proved to be poorly adapted to low-density thermal insulators notably due to edge effects, which disturb the temperature rise. To overcome this problem, the hot-ring method, which is very close to the hot-wire technique, could be interesting as it does not make any assumptions on the dimensions of the heating elements. In order to investigate the use of this method for measurements on low-density thermal insulators we conducted a theoretical and experimental study on several expanded polystyrene (EPS) foam samples. The numerical model developed solves the 2-D axisymmetric heat transfer around the ring taking into account the conduction–radiation coupling and the inertia of the element. Numerical and experimental results show that classical hot-ring apparatus are poorly adapted to measurements on low-density insulators owing to the thermal inertia of the elements. However, we developed a modified identification procedure eliminating the influence of the inertia of the apparatus on the measured thermal conductivity. This new procedure gives accurate results even for EPS foams, which could not be considered as optically thick. Thus, the hot-ring technique could be extended to low-density thermal insulators. |
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