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Abstract
A constant volume sorption technique has been developed which greatly accelerates the measurements of gas permeation in closed cell foam insulation. Unlike standard gas transmission devices, the new sorption apparatus determines the effective diffusion and solubility coefficients independently in a single test. The ceffective diffusion coefficient is used as in input to a computational model which predicts the rate of k-factor aging in a foam insulation panel. The effective solubility coefficient is used primarily to understand the behavior of the blowing agent in the foam system, and therefore, is of particular interest in the screening of alternative non-CFC blowing agents. The basis of the new technique is the measurement of the transient pressure in an isolated, constant-volume chamber containing the foam sample and the test gas, immediately after the test gas pressure surrounding the sample has been increased or decreased in a step fashion. The transient diffusion equation for the appropriate sample/chamber geometry is solved and the solution is used to generate the effective diffusion and solubility coefficients from the transient pressure curve. The device geometry is determined in part by using a pycnometer type measurement of the test chamber and sample volumes. One of the advantages of the technique is the simplicity of its physical implementation and its ease of operation. There are however, several aspects of the measurement system which mush be given careful consideration to ensure meaningful results. This paper focuses on these important practical details of the tecnhique. In general the more subtle aspects of the measurement systems are related to non-ideal conditions which cause divergence from the indealized model of the measurement process. For example, if the imposed pressure steip is too large, the foram sample may deform slightly during the test, thereby invalidating the assumption of constnat chamber and sample volumes. FOr each of the non-ideal patterns, the magnitude of the effects on the results is examined and methods for minimizing this effect are discussed.
A constant volume sorption technique has been developed which greatly accelerates the measurements of gas permeation in closed cell foam insulation. Unlike standard gas transmission devices, the new sorption apparatus determines the effective diffusion and solubility coefficients independently in a single test. The ceffective diffusion coefficient is used as in input to a computational model which predicts the rate of k-factor aging in a foam insulation panel. The effective solubility coefficient is used primarily to understand the behavior of the blowing agent in the foam system, and therefore, is of particular interest in the screening of alternative non-CFC blowing agents. The basis of the new technique is the measurement of the transient pressure in an isolated, constant-volume chamber containing the foam sample and the test gas, immediately after the test gas pressure surrounding the sample has been increased or decreased in a step fashion. The transient diffusion equation for the appropriate sample/chamber geometry is solved and the solution is used to generate the effective diffusion and solubility coefficients from the transient pressure curve. The device geometry is determined in part by using a pycnometer type measurement of the test chamber and sample volumes. One of the advantages of the technique is the simplicity of its physical implementation and its ease of operation. There are however, several aspects of the measurement system which mush be given careful consideration to ensure meaningful results. This paper focuses on these important practical details of the tecnhique. In general the more subtle aspects of the measurement systems are related to non-ideal conditions which cause divergence from the indealized model of the measurement process. For example, if the imposed pressure steip is too large, the foram sample may deform slightly during the test, thereby invalidating the assumption of constnat chamber and sample volumes. FOr each of the non-ideal patterns, the magnitude of the effects on the results is examined and methods for minimizing this effect are discussed.
Date
9/1998
9/1998
Author(s)
T R Brehm; L R Glisckman
T R Brehm; L R Glisckman
Page(s)
25
25
Keyword(s)
gas permeation; closed cell foam; sorption technique; solubility; gas diffusion; k-factor
gas permeation; closed cell foam; sorption technique; solubility; gas diffusion; k-factor