Measurement of diffusion coefficients of VOCs for building materials: review and development of a calculation procedure
Haghighat, F., Lee, C. and Ghaly, W. S.
2002
Indoor Air, 12 (2), 81-91
Haghighat, F., Lee, C. and Ghaly, W. S., (2002), "Measurement of diffusion coefficients of VOCs for building materials: review and development of a calculation procedure", Indoor Air, 12 (2), 81-91.
| Abstract: |
| The measurement and prediction of building material emission rates have been the subject of intensive research over the past decade, resulting in the development of advanced sensory and chemical analysis measurement techniques as well as the development of analytical and numerical models. One of the important input parameters for these models is the diffusion coefficient. Several experimental techniques have been applied to estimate the diffusion coefficient. An extensive literature review of the techniques used to measure this coefficient was carried out, for building materials exposed to volatile organic compounds (VOC). This paper reviews these techniques; it also analyses the results and discusses the possible causes of difference in the reported data. It was noted that the discrepancy between the different results was mainly because of the assumptions made in and the techniques used to analyze the data. For a given technique, the results show that there can be a difference of up to 700 in the reported data. Moreover, the paper proposes what is referred to as the mass exchanger method, to calculate diffusion coefficients considering both diffusion and convection. The results obtained by this mass exchanger method were compared with those obtained by the existing method considering only diffusion. It was demonstrated that, for porous materials, the convection resistance could not be ignored when compared with the diffusion resistance.
Practical Implications
The diffusion coefficient is inferred from experimental measurements; therefore, great care has to be given to the physical modeling of the experimental setup. In particular, the values of diffusion coefficients reported without reference to airflow conditions will be inaccurate and can be misleading to designers and modelers. After presenting a summary of the different techniques for measuring the diffusion coefficient, the paper proposed an approach, namely the mass exchanger, for analyzing the experimental results, which would make the diffusion coefficient independent of the test conditions. |
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