Press Drying Technology And Properties Of Heat Transmission And Mass Transfer Of Bamboo Timber Of Dendrocalamus Giganteus

In this dissertation, press drying technology and properties of heat transmission and mass transfer of bamboo timber of Dendrocalamus giganteus were studied during press drying process.Following the relevant theory and research approaches of drying behaviors and permeability of wood, the systemic research on the drying behaviors and permeability of bamboo timber of Dendrocalamus gigangteus was firstly carried out, and drying behaviors and penneability of bamboo timber were firstly measured and analyzed. The results indicated that the pretreatment methods and the structure of bamboo have significant effects on the drying behaviors. The shrinkage rate of the knotless section of bamboo timber is bigger in the radial direction than that in the tangential direction and the longitudinal direction .The shrinkage rate in the tangential direction differed from that in the radial direction, but no splits occurred on the bamboo timber during drying process.The fluid permeability of bamboo timber is higher in the longitudinal direction than that in the tangential direction and in the radial direction; the fluid permeability could be improved by pretreating the sample and by decreasing the moisture content of sample as well.Research on drying technology of bamboo timber was accomplished via hot pressing method for the first time. The results showed that the drying rate could be raised and the drying efficiency could be improved by water-soak pretreatment, the platen temperature had distinct effect on the drying technology and the drying quality of bamboo timber. The optimum parameters of hot-pressing drying method, which were developed synthetically, were as follows: soaking for 3h in water with a temperature of 60℃, a platen temperature of 150℃, a pressure of 0.2 MPa with a breath interval of 5 minutes.The moisture movement was mainly controlled by both temperature gradient and moisture gradient The higher the drying temperature was, the bigger the moisture diffusion coefficient would be at every drying stage. The moisture diffusion coefficient was increased at the early stage of drying when the moisture content was high and was up to the maximum value when the moisture content of the sample drew near to fiber saturation point, and then decreased gradually with decreasing of the moisture content.The intuitionistic numerical mathematical model of heat transmission and water transfers was firstly established. The verification experiment of the model indicated that the model could approximately reflected the law of heat transmission and water transfers during the dryingprocess.The samples dried via hot pressing method had better dimension stability, mechanical properties and bonding ability than those of samples air-dried. After drying with hot press, the surface density of bamboo was increased and vertical density distribution tended to be even.