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Table 65. Measured diffusion coefficient values and ratios in the R, T and L directions, for C. citriodora and E. obliqua E. marginata E. pilularis Db (m2/s) Average Ratios Db (m2/s) Average Ratios 2.54E-11 2.57E-11 2.63E-11 3.69E-11 3.81E-11 3.82E-11 2.81E-10 2.72E-10 2.60E-10 R/T 2.58E-11 0.68 L/T 3.77E-11 7.19 L/R 2.71E-10 10.50 R/T 2.51635E-11 2.67E-11 1.61 2.76678E-11 2.73334E-11 1.78046E-11 1.63278E-11 1.66E-11 14.18 1.56768E-11 L/R 2.63111E-10 2.35E-10 8.81 2.20932E-10 2.22006E-10 L/T Direction Sample 1 2 3 1 2 3 1 2 3 E. obliqua Db (m2/s) Average Ratios C. citriodora Db (m2/s) Average Ratios 6.56E-11 7.34E-11 7.24E-11 4.22E-11 3.97E-11 3.97E-11 9.55E-10 1.04E-09 1.09E-09 R/T 7.05E-11 1.74 L/T 4.05E-11 25.36 L/R 1.03E-09 14.59 1.54E-11 1.31E-11 1.44E-11 1.35E-11 1.42E-11 1.56E-11 6.39E-11 6.26E-11 5.40E-11 R/T 1.43E-11 0.99 L/T 1.44E-11 4.17 L/R 6.02E-11 4.21 4.4.5 Shrinkage For each shrinkage sample, we generated plots of shrinkage, MC and dew point temperature as a function of time and shrinkage as a function of MC. A typical output of the experimental data is shown in Figure 62 collected for a micro-sample of Eucalyptus pilularis. For the first drying cycle, at high relative humidity, very little shrinkage occurs in both the radial and tangential directions, as the samples surface remains above FSP. The sample reaches equilibrium, as shown by the plateau of shrinkage and moisture content, before the shrinkage rate gently increases with decreasing humidity (represented by the dew point temperature). The MC steadily decreases during this period. At the end of the plateau we increase the relative humidity, where the sample picks up moisture and swells. Even though equilibrium is not fully attained, either through desorption or adsorption, a hysteresis effect is apparent, as the MC is less in adsorption than desorption. The same data can be plotted as a shrinkage versus MC curve as shown in Figure 63. Note that the data defines a very accurate curve during the test period as the adsorption/desorption shrinkage closely follows the same curve (low MC tail of the graph). This lack of hysteresis evident in shrinkage versus MC curves compared to the hysteresis evident in the shrinkage and MC versus time curves is consistent with published data (Perré, 2007b). Observation of the curve distinguishes two different phases: the removal of free water with minimal shrinkage starting above the fibre saturation point, and a noticeable shrinkage phase, denoting the removal of bound water with a linear relationship with MC. 75 30 60 Total shrinkage MC Tangential Dew point temperature Radial 45 30 15 20 10 00 0 10 20 30 40 Time (h) Figure 62. Typical experimental data (MC, tangential and radial shrinkage, and dew point temperature versus time) collected with a Eucalyptus pilularis micro- sample. Figure 63. Typical experimental data expressed as shrinkage (radial and tangential) versus MC with a Eucalyptus pilularis micro-sample 102 Evaluation of super–heated steam vacuum drying viability and development of a predictive drying model for Australian hardwood species – Final report Shrinkage intersection point Moisture content (%) Longitudinal T angential Radial Temperature (°C), shrinkage (%)PDF Image | Evaluation of super-heated steam vacuum drying
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