Veterinary and Agricultural Sciences Collected Works - Theses

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    Microwave drying and conditioning of Pinus radiata D. Don sawn timber
    Abdul Latif, Nur Hannani ( 2014)
    Microwave (MW) processing technology is used for the conditioning of wood to specific moisture contents (MC), generally 12%. MW drying differs from conventional drying in the way MW energy interacts with wood moisture and its superior penetration. Wood moisture content can be quite variable towards the end of drying. MW processing reduces the within charge moisture variation. The objective of this study is to model energy requirements as a function of starting wood moisture content and wood species. The methodology involves investigating the influence of microwave conditioning technology in reducing wood drying time and also wood drying degrade, due to moisture leveling, assisting stress relaxation and avoiding case hardening of Pinus radiata by using laboratory scale and pilot scale microwave technology. For laboratory scale experiments, research methodology involved oven-drying boards for a range of hours (to get a range of moisture contents) and then conditioning boards with MW energy until the final weight of each board achieved the equivalent of 12% MC. It was found that there is a strong correlation between moisture content after oven drying and the number of microwave passes needed to achieving a final board of 12% moisture content. Drying quality assessment after microwave processing revealed that checking had occurred and there were some limitations in evaluating warping on samples due to the limitation of specimen size. Pilot scale microwave drying was then conducted to scale up and validate laboratory scale microwave research and further evaluate the effectiveness of dynamic microwave processing in optimizing drying with minimal defects. A comparison of sapwood only, mixed sapwood & heartwood and heartwood only was determined. From this study, it was shown that microwave drying time was fastest for heartwood samples and that microwave energy consumption was about 206 kW/h. The moisture content distribution in boards was also uniform and residual stress tests found that almost 90% of boards were free of case hardening. It can be concluded that the application of microwave conditioning is an efficient method of drying timber. Drying times are fast and there are minimal drying defects.