Study On Dehumidification Drying Characteristic And Microstructure Charactterization Of Three Kinds Of Precious Wood

In order to explore the best drying process of precious wood, in this paper, the three kinds of precious sawn timber iron,ambila,monzo as the research object, using heat pump dehumidification drying of these three kinds of timber and analysis of woods drying characteristics and microstructure. Research focuses on the analysis of three kinds of sawn timber drying process of drying characteristics, such as drying curve, moisture content, moisture content deviation, stress, dry shrinkage etc. With the means of CT non-destructive scanning technology establishes a mathematical model of sawn timber moisture content and CT value, and used the model analyzes the three kinds of sawn timber layer moisture content. On this basis, using microscope and scanning electron microscopy observed the micro-structure of the three kinds of sawn timber, determine the relationship between microstructure and dried sawn timber grades. The results showed that:(1) Physical properties of the three kinds of sawn timber and heat pump system selection1) Physical propertiesThe three kinds of sawn timber,iron,s density and dry shrinkage coefficient is the sma-llest, basic density is 0.62g/cm3,tangential shrinkage coefficient is 0.54%,ambila,s basic d-ensity is 0.84g/cm3,tangential shrinkage coefficient is 0.47%,monzo,s density is the largest ,its basic density is 0.94g/cm3,air dry density is 1.14g/cm3.2) Heat pump system selectionCompressor 1HP;evaporator with heat pump 6.8m2;dehumidification evaporator 5.3 m2;condensator 8.3 m2.(2) Primary drying schedule and characteristics during the drying process of three kinds of sawn timber1) Primary drying schedule of three kinds of sawn timber as shown in table 13 to 15.2) Characteristics during the drying processThrough the analysis of three kinds of sawn timber drying process of drying characteristics, such as drying curve, moisture content, moisture content deviation, stress, dry shrinkage etc.the results showed that:The thickness of sawn timber moisture content difference becomes larger.the more prone to drying stress,the timber is more prone to shrinkage deformation.when the sawn timber moisture content near the fiber saturation point or below the fiber saturation point, will appear dry shrinkage deformation.3) The relationship of moisture content and the CT value during the drying processUsing non-destructive CT scanning technology to detect three kinds of sawn timber CT values during different drying stage, and linear fitting moisture content and CT value of each stage.lt is concluded that the three kinds of sawn timber iron,ambila,monzo linear regression equation of CT value and moisture content respectively:y=0.1965x+66.942,R2= 0.9888;y=0.1498x+18.907,R2=0.9903;y=0.0710x-15.442,R2=0.9876.Using moisture cont-ent distribution is further verified the fitting equation,shows that with this method,by using X ray non-destructive scanning method to measure the moisture content distribution of dr-ying process is feasible.(3) Drying grade and drying scheduleThree kinds of sawn timber drying quality level to be assessed,among them, the iron moisture content and stress indicators have reached the national second material standard, visible defects indicators have reached the national first material standard;ambila moisture content and stress indicators have reached the national second material standard, visible defects indicators have reached the national first material standard;monzo moisture content and stress indicators have reached the national second material standard, visible defects indicators have reached the national second material standard.At the same time that deawn the drying schedule of 20mm thick the three kinds of sawn timber iron, ambila, monzo (Table 31-33),To provide a theoretical basis and technical parameters for three kinds of sawn timber drying process.(4)Microstructure charactterizationThrough the comparative analysis of microscopic structure of the three kinds of sawn timber,the distribution of parenchyma cells and ray cells are small influence on wood drying process. Iron vessel containing a small amount of tylosis, ambila contains larger of parenchyma cells, part of the cells occurred shrinkage after drying process, there are a large number of tylosis within monzo cell cavity, block the moisture movement in the channel,so monzo is the hardest dried wood,and prone to drying defects, Iron is relatively easy to be dried.