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T able 32. V acuum Trial MC change points (%) Heat-up Green - 70 70 - 60 60 - 50 50 - 40 40 - 30 30 - 25 25 - 20 20 - 15 15 - final Equalise (48 hrs) drying schedules - Eucalyptus pilularis BBT4 WBD (°C) 2.1 2.4 2.4 2.4 3.2 4.4 7.7 9.5 14.0 13.0 5.4 BBT1 BBT2 BBT3 DBT (°C) WBD (°C) EMC (%) DBT (°C) WBD (°C) EMC (%) DBT (°C) WBD (°C) EMC (%) 44 2.1 18.0 44 3.0 15.0 44 3.4 14.0 45 4.0 13.0 45 4.4 13.0 45 5.2 12.0 48 6.7 10.0 53 9.5 9.0 60 14.0 6.7 67 13.0 6.9 44 2.1 18.0 44 2.6 16.0 44 3.2 15.0 45 3.8 14.0 45 4.4 13.0 45 5.2 12.0 48 7.7 10.0 53 9.5 9.0 60 14.0 6.7 67 13.0 6.9 44 2.1 18.0 44 2.8 16.0 44 2.8 16.0 45 2.8 16.0 45 3.4 15.0 45 4.6 13.0 48 7.7 10.0 53 9.5 9.0 60 14.0 6.7 67 13.0 6.9 70 6.5 11.0 67 5.4 12.0 67 5.4 12.0 DBT (°C) 44 44 44 45 45 45 48 53 60 67 67 EMC (%) 18.0 17.0 17.0 17.0 15.5 13.5 10.0 9.0 6.7 6.9 12.0 Moisture content The initial MC results are shown (Table 33). For each trial, initial MC populations were not normally distributed, likely because of high MC outliers (Figure 32). Multiple pairwise comparisons produced no significant differences between sample population trials BBT1 and BBT2, and BBT1 and BBT3. All other pairwise comparisons produced significant differences. 110 BBT1 100 90 80 70 60 50 40 30 20 BBT2 BBT3 BBT4 Table 33. Initial MC results – E. pilularis Trial Average Maximum Minimum Standard deviation Initial MC (%) BBT1 BBT2 BBT3 BBT4 53.8 54.6 51.3 44.2 85.6 96.9 103.0 85.8 33.8 30.1 36.3 23.4 9.0 11.7 11.6 11.8 Figure 32. Scattergram of initial MC – E. pilularis For trials BBT2 and BBT3, we recorded significant differences between the final cross-sectional MC population means of end-matched conventional and vacuum trials (Figure 23 and Table 20). No significant difference was recorded for the BBT1 trials. In accordance with both AS/NZS 4787:2001 and AS 2796:1999 BBT2 and BBT3 conventional trials did not achieve acceptable grade quality in terms of average final cross-sectional MC because of over-drying. All other trials achieved acceptable grade quality. It can be observed that by increasing the equalisation EMC from 11% to 12% between the first BBT1 vacuum trial and subsequent vacuum trials, the spread (standard deviation) of final cross-sectional MC was reduced. Personal communications with Hurford Hardwood management (Engwirda, 2009), reveal tougher limitations are imposed on final cross- sectional MC variation for E. pilularis than those specified by AS 2796:1999 (Standards Australia 1999) and AS/NZS 4787:2001 (Standards Australia 1999). This is particularly true for strip flooring where a final cross–sectional variation of ± 1% is imposed for a target final MC of 10.5%. With respect to these specifications, the variation of final cross–sectional MC for all trials except for the BBT1 conventional trial is unacceptable. 69 Evaluation of super–heated steam vacuum drying viability and development of a predictive drying model for Australian hardwood species – Final report Initial MC (%)PDF Image | Evaluation of super-heated steam vacuum drying
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