Abstract
Introduction
Labeling system of building material corresponding to formaldehyde emission rate started in 2003 in Japan. Basically, formaldehyde emission rate from building materials should be measured by small chamber method based on JIS A 1901, in the meantime, desiccator method, i.e. head space method, has been widely used as an alternative. Recently, market supply of glass desiccator specified by JIS R 3503 was canceled and there is no prospect of future production, so there is a need for an alternative to existing desiccators. Hence, it is necessary to investigate the various alternative desiccators on the market specified by ISO or DIN and to clarify performance related formaldehyde emission test.
This paper reports the results of three-dimensional digital modeling for four types of alternative desiccators on market and conducts the numerical analysis of diffusion phenomenon in their desiccators. Since the geometric shape in the desiccators for each product and the relative distance from the surface of test building materials to the water surface as an adsorbent were also different, equivalent diffusion length scale, ‘Ld’, corresponding to hypothetical one-dimensional diffusion distance for each desiccator were numerically analyzed.
Methods
Three-dimensional laser scanner was used to create the three-dimensional digital models of inner geometries for five types of desiccator on market. The detail geometries of test specimen as formaldehyde emission material were also reproduced in desiccators. Numerical analysis for formaldehyde emission, diffusion, and sorption inside desiccators were carried out for targeting five types of desiccator geometries.
Results
As a result, the equivalent diffusion length scale ‘Ld’ of the four desiccators, i.e., the alternative four desiccators (model A, B, C, and D), differs by about 25% compared to the current desiccator model R.
Conclusions
Because of the geometry discrepancies between desiccators depending on the type and the differences of vertical distance from water surface (adsorbent) to the test specimens, each type of desiccator have different ‘Ld’, the equivalent diffusion length scale corresponding to one dimensional diffusion length from the others. Therefore, it is necessary to calibrate experimental result using Ld. The time constant τe defined by equation (6) was almost proportional to the relative magnitude relation of the diffusion time scale τD of equation (5). The time constant τe of each desiccator was around 20 to 120 seconds and the diffusion time scale τD was about 0.6 to 1 hours.
