Mathematical model of heat and moisture transfer in alder birch wood during the thermo-vacuum treatment and its application in the quantitative control of the wood color

High-temperature heat treatment (HTHT) is an effective method for improving the wood dimensional stability and biological durability at present. However, the quantitative control of the wood color during the HTHT has been a more difficult problem for a long time. To solve the problem of quantitative control of wood color under the thermo-vacuum treatment (TVT) process, the mathematical model of heat and moisture transfer in alder birch wood (Betula alnoides) during the TVT process was built, and its application in the quantitative control of the wood color was also studied. (1) The experimental values and the model values of heat and moisture transfer in wood were found to be in good agreement. (2) The changes of wood temperature and moisture content (MC) were influenced obviously by the heat treatment temperature, the initial MC, and the thickness of specimen as well. The higher the heat treatment temperature was, the more rapid was the rise in the wood temperature and the drop in MC. The higher the initial MC of the wood was and the thicker the wood got, the slower the rise in wood temperature and the drop in MC. (3) Based on the mathematical model of heat and moisture transfer during the TVT process and the wood color index difference regression equations in the function of the temperature and time, the quantitative control of alder birch wood color during the TVT process was achieved. Therefore, it is feasible that heat and mass transfer principle applied during the TVT process guided the wood color quantitative control.     

Effect of microwave heating on compressive strength of beech wood (Fagus sylvatica L.) parallel to grain

This article deals with the changes of strength of beech wood (Fagus sylvatica L.) when compression load is applied parallel to grain and the wood is heated using microwave (MW) energy for a time period determined by two variants of drying. The elasticity modulus and compressive strength parallel to grain were measured using a universal testing machine in accordance with a relevant technical standard. Regression equations describing the dependence of compressive strength on wood density were determined for both variants of heating with a given load. Furthermore, a three-factor analysis of variance was performed to verify the significance of possible factors influencing changes of wood strength and elasticity. Possible hypotheses of changes caused by MW heating and the significance of discovered factors are also discussed. The results showed reduction of average values of wood compressive strength parallel to grain. The values were reduced by 35% in variant 1 and by 41% in variant 2 as opposed to wood to which no MW energy was applied. The difference in strength between the variants was nearly 9%.