The influence of wood microwave drying technology at home and abroad
Because the microwave drying technology of wood can not be compared with the conventional drying technology to lower moisture content, the microwave drying can make the wood parallel to the grain, and the hardness of this technology direction was higher in the 1950s and 1960s. The hardness of dried wood with different final moisture content at home and abroad is not affected by temperature level.
A large number of research results are mainly concentrated on the establishment of microwave drying equipment, the development of drying equipment for wood discoloration and the dielectric properties of wood in microwave electromagnetic field.
In recent years, with the rapid development of various degree detection technologies, microwave technology is becoming more and more mature, microwave equipment A Dedic and other people compared beech and fir drying of the continuous improvement of the technology has made new progress in testing, determine the microwave drying efficiency and low energy consumption advantages, and foreign research progress pointed out that Combining conventional drying with microwave drying and exploring the basic characteristics of wood during microwave drying abroad, using conveyor belts to load wood for drying can improve the physical and chemical properties of dry wood, formulate drying technology, apply testing technology, and S. Vongpradubchai et al. The results show that the new drying method can improve the drying quality of dry wood. Comparing with other drying methods such as modeling and simulation, high efficiency and energy saving, continuous microwave belt drying equipment has been used for wood drying.
M Leiker et al. with short processing time, uniform heating, high energy efficiency and good drying quality studied the adsorption of wood after drying by vacuum microwave drying, microwave drying and regular drying. It was found that the wave power of input micro-AL. Anti et al. through infrared camera technology and CT scanning technology was affected the balance of water content of wood. The main difference between the dry and wet wood during drying is the difference in the field distribution and the presence of wood factors. H Sahin et al. Used microwave with a frequency of 245GHz to study the phenomenon of uneven dryness.
LHansson et al. used microwave imaging techniques to measure the dielectric properties of three broad-leaved wood species, Populus nigra, Alnus alder and Beech. It is found that the dielectric properties of wood in different structural directions are different, and dielectric studies show that the lower the moisture content of wood, the smaller the attenuation constant and dielectric loss factor increase with the increase of moisture content in a certain range. P. Aggarwal et al. took silver birch board as drying object, P Zielonka et al. measured the temperature distribution on the cross section of spruce wood when microwave radiation time, initial moisture content, auxiliary heating and thickness drying were studied at 245 GHz, and determined the influence of Fourier on drying rate and board quality.
The results show that the theoretical calculation model based on the heat loss conduction equation of water dispersion can basically keep the actual drying rate constant, the influence of initial moisture content on it is not significant, and the auxiliary heating temperature distribution can be described qualitatively. In addition, P Zielonka et al. showed that microwave drying at 245 GHz accelerated wood drying. A. Oloyede et al. pointed out that microwave drying reduced the mechanical strength of dried wood by about drying, compared with natural drying and conventional drying, which occurred several millimeters away from the surface of dried wood. The highest temperature appears on the surface of the dry wood.
L Hansson et al 20%~60%. JS. Machado et al. analyzed the microwave scattering of oak wood during drying by finite element modeling. It was found that the longer the microwave radiation time was, the faster the drying rate was. However, the measured values of oak wood were in good agreement. P. Rattanadecho makes the deviation of moisture content larger. Furthermore, the long-term microwave treatment led to the simulation experiment of wood microwave drying with rectangular waveguide tubes, and the compressive strength of the wood was significantly reduced. L Hansson et al. used principal component analysis (PCA) to analyze the distribution of field energy and temperature in drying process. Microwave irradiation method and classical statistical test method were discussed. The effects of irradiation time, working frequency and wood size on drying performance of microwave drying and conventional drying were compared. The differences of elastic modulus and static bending strength of wood after microwave drying were compared.
The results showed that the two drying methods could be used as a guide for wood drying, compared with the basic parameters of microwave drying and the parameters of water extraction rate, tree age and density. SKadem et al. used a comprehensive 3D heat and mass transfer method to calculate the difference in the mechanical strength of wood. Under the experimental conditions, there was no obvious model to study the temperature, moisture content and its works during microwave drying of wood. Based on the variation of temperature sensor and energy absorption characteristics, M Leiker et al. used FEMLAB model to process and analyze the microwave vacuum drying veneer experiment.
Finally, it is pointed out that besides the drying characteristics which are consistent with the experimental conditions, it is helpful to design the drying equipment for wood mechanical properties and optimize the microwave drying process. Compared with conventional drying and microwave drying alone, R Seyfarth et al. proposed that microwave drying and vacuum drying were the least affected