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After extensive literature review, very little work measuring gas permeability in all three directions has been conducted. For comparative purposes, Table 64 includes permeability data for the softwood Pinus taeda (Milota et al., 1995) and the hardwood Quercus falcata (Perré, 2007a). The gas permeability data for Quercus falcata was the lowest gas permeability for a hardwood species this author could find. The four species measured in this report were still at least a factor of 10 less permeable than the lowest published figure, demonstrating the high impermeability of Australian hardwoods. Table 64. L-R-T average permeability results for each species Pinus taeda (Milota,1995) Quercus falcata (Perré,2007) Species E. obliqua 19.3 17.6 5.55E-14 74.4 7.8 8.60E-18 74.5 8.0 2.95E-19 6400 189000 29.2 E. marginata E. pilularis 19.6 19.6 17.3 16.8 6.74E-14 3.50E-14 73.9 74.6 7.9 7.8 4.68E-20 1.44E-20 74.1 74.2 8.0 7.8 4.41E-16 1.70E-20 1440000 2440000 150.0 2060000 0.0001 0.846 C. citriodora 19.7 17.0 7.65E-17 74.3 7.9 N/A 74.1 8.0 3.44E-21 N/A 22000 N/A Diameter (mm) Length (mm) Permeability (m2) Diameter (mm) Length (mm) Permeability (m2) Diameter (mm) Length (mm) Permeability (m2) L/R L/T R/T 1.01E-05 6.90E-13 2.00E-07 N/A 7.30E-08 N/A 50 140 2.74 110000 143000 1.3 4.4.4 Bound water diffusion Figure 58 to Figure 61 show the evolution of mass loss per unit volume over time of radial, tangential and longitudinal disc samples for each species. As radial and tangential sample diameters were much larger than those in the longitudinal direction, and because the samples were of slight varying thickness the mass loss was ‘normalised’ by dividing by the mass loss per unit volume. Both figures show two distinctive groups of curves, one of small slopes and one of extensive bigger slopes. The big slope represents fluxes of water vapour in the longitudinal direction, and the small slopes through the radial and tangential directions. The vapour flux in all directions is markedly lower for C. citriodora than for E. obliqua, with the other species falling in between. This may be attributed to the vast anatomical and chemical differences between these species. We specifically chose these species for this research based on their highly diverse wood property, chemistry, anatomical and drying capabilities. Table 65 contains the measured diffusion coefficient results in the radial, tangential and longitudinal directions for each species. Average values are shown along with the direction ratios. Because three samples were used per species direction (labelled R1..R3, T1..T3 and L1.. L3 for the radial, tangential and longitudinal directions, respectively), standard deviation values are not included. C. citriodora diffusion coefficients were much lower in all directions compared with the other species, where E. obliqua was the highest. The R/T ratio of diffusion coefficient for C. citriodora was approximately 1:1 indicating low diffusion isotropy in this plane. This is evident in many other wood property ratios measured for this species in this report, such as 100 Evaluation of super–heated steam vacuum drying viability and development of a predictive drying model for Australian hardwood species – Final report Anisotropy ratios Tangential Radial LongitudinalPDF Image | Evaluation of super-heated steam vacuum drying
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