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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

TRANSIENT DETERMINATION ON THE WATER VAPOR DIFFUSION COEFFICIENT OF AUTOCLAVE AERATED CONCRETE: EFFECTS OF SAMPLE AND SENSOR SIZES

Get access (open in a dialog) DOI: 10.1615/IHTC16.tpm.022415
pages 8629-8636

Resumo

The effects of sample and sensor sizes on the transient measurement results on the water vapor diffusion coefficient of autoclave aerated concrete (AAC) were investigated. Based on the analytical solution to a 1-D mass transfer problem, transient measurements were performed with square cylindrical AAC samples maintaining at a differential relative humidity gradient from nearly 0 to 80%. The axial sample length along the water vapor diffusion direction was varied from 120 mm to 250 mm while having a constant cross-sectional area of 50 × 50 mm2. Two sizes of rodlet-shaped hygric sensors with diameters of 6 mm and 12 mm were utilized. The water vapor diffusion coefficient was also measured using the standard steady-state method as a reference. Results showed that the transient measurement results decrease with increasing the sample length due to the longer and more complex paths for water vapor diffusion. The transient results of 150 mm sample with 6 mm sensors were found to have the best agreement with steady-state results with an overall deviation less than 8% and a measurement time being about 60 h. The deviations between transient and steady-state results of 200 mm and 250 mm samples increase to 27% and 64%, respectively, because the departure of the water vapor diffusion from the 1-D physical model is exaggerated when increasing the sample length. The deviation increases slightly to 14% when 12 mm sensors were adopted on the 150 mm sample, which indicates that the sensor size has less effect on the transient results. The sample length of ~150 mm with 6 mm hygric sensors is recommended for the transient measurements on the water vapor diffusion coefficient of the select AAC material.