Research On Characteristics Of Wood Microwave Drying

This thesis, using Masson pine as experiment material, systematically studied the factors that had effects on the utilization efficiency of microwave (MV) energy and the wood drying rate, as well as concluded the laws of variations in temperature of wood and its inner vapor pressure during the process of MV drying. To provide scientific basis and theoretical support for the application of MV drying, this thesis theoretically analyzed, during the process of MV drying, the transport mechanism of heat quantity and water content through wood, and set up caloric transport model, verifying this model on the basis of experiment. The main conclusions and original points can be showed as the following:1. This thesis initially compared the wood drying rate and utilization efficiency of MV when input MV energy continuously and intermittently. When input MV energy intermittently, the water content of wood varied with gradient as the drying time continued. The longer the intermittent time was, the more obvious the gradient trend was. The water content of wood significantly reduced as MV radiated and gradually reduced as MV radiation ceased. The average drying rate with continuous radiation by MV energy was higher than with intermittent radiation. However, microwave energy utilization efficiency with intermittent radiation was higher than with continuous radiation. The average drying rate and microwave energy utilization efficiency above the fiber-saturation point(FSP) was higher than below the FSP no matter what radiation pattern was used. Different patterns of intermittent radiation had different effects on microwave energy utilization efficiency.Using proper pattern of intermittent radiation to dry wood could obviously improve utilization efficiency of MV.2. The thesis initially studied the character of variation in temperature and vapor pressure through wood in the process of drying wood by intermittent radiation of MV. The temperature through wood varied periodically when input MV energy periodically. Generally, during this process, the variation trend of temperature showing fluctuating could be divided into three stages: high-speed-temperature stage; constant- temperature stage; later stage of rising temperature. Under the same power of MV radiation, the wood's temperature with intermittent radiation was lower than with continuous radiation. Proper intermittent radiation of MV could effectively avoid wood's carbonization in later drying stage.