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Abstract
In several types of cellular plastics used as thermal insulation, a gas of low thermal conductivity is used as blowing agent. This gas will, if it remains in the cells of the final product, have a favorable effect on the thermal insulation properties of the foam. Since the material contains a gas which has low concentration in air, the cell walls are subjected to a large differential partial pressure and there is, therefore, a risk that air will diffuse inwards and the gas used will diffuse outwards, with an increase in the thermal conductivity of the material as a result. It is a complicated matter to lay down practical value of thermal conductivity for a material whose conductivity changes with time. It most countries, some type of correction term is used to convert values. In the following, only that part of the correction will be treated which is due to the changes in thermal conductivity with time, often referred to as aging allowance. In order that the magnitude of the allowance may be determined, the variation of thermal conductivity as a function of time must be known.
In several types of cellular plastics used as thermal insulation, a gas of low thermal conductivity is used as blowing agent. This gas will, if it remains in the cells of the final product, have a favorable effect on the thermal insulation properties of the foam. Since the material contains a gas which has low concentration in air, the cell walls are subjected to a large differential partial pressure and there is, therefore, a risk that air will diffuse inwards and the gas used will diffuse outwards, with an increase in the thermal conductivity of the material as a result. It is a complicated matter to lay down practical value of thermal conductivity for a material whose conductivity changes with time. It most countries, some type of correction term is used to convert values. In the following, only that part of the correction will be treated which is due to the changes in thermal conductivity with time, often referred to as aging allowance. In order that the magnitude of the allowance may be determined, the variation of thermal conductivity as a function of time must be known.
Date
9/1989
9/1989
Author(s)
Ingvar Sandberg
Ingvar Sandberg
Page(s)
16
16
Keyword(s)
cellular plastic; thermal conductivity; gas filled plastic
cellular plastic; thermal conductivity; gas filled plastic