Determination of the thermal radiation and thermal conductivity of solid PUR in preinsulated pipes for district heating

The test indicate that measuring the contribution of radiation with infrared spectrophoto-meter using direct detector cannot be used, as it i.e. can lead to results showing that radiation falls at rising temperature. When measuring with a hemispherical detector the expected development of the contribution of radiation is obtained. Thermal conductivity at radiation is calculated to be 0.0048 W/(m K) where it originally was calculated to be 0.0031 W/(m K) or an increase of 55%. Total calculated thermal conductivity increases by 0.0005 W/(m K) so the difference between the calculated and the measured is narrowed to 4% of total thermal conductivity. Ageing tests show that the contribution of radiation of thermal conductivity remains constant in the lifetime of the pipes at working temperatures below 100 deg. C. the contribution of radiation increases with temperatures from 0.0048 W/(m K) at 50 deg. C over 0.0078 W/(m K) at 100 deg. C to 0.0121 W/(m K) at 150 deg. C. Exploratory measurements in connection with the project show that there is reason to believe that infrared spectrophotometry can be used as an on-line substituting measurement for the compressive strength of cellular plastics. The lifetime of cellular plastics can be estimated with great accuracy when determining the rate of closed cells in cellular palstics, which are thermally aged in oxygen-tight bottles