The application of microwave technology is mainly based on its electromagnetic properties. In the application of ultra-high frequency, it can transmit more media, so it is widely used in the communication industry. However, microwave with frequencies of 915MHz and 2450MHz can also be used for industrial heating. By polarizing water molecules, water can be quickly separated, and drying rate of industrial materials can be improved. In wood processing, microwave heating technology has been gradually introduced, which not only improves economic benefits, but also realizes the production process of environmental protection.
Present Situation of Wood Drying Technology in China
Since the reform and opening up, China's wood drying industry has developed rapidly and has become a perfect industry system.With the increasing use of wood, the wood drying market is more prosperous, which brings a good opportunity for the rapid development of wood drying industry in China. At present, China's wood drying industry has the following characteristics.
1. The drying consciousness of wood processing enterprises is enhanced. Simple air-drying or smoking-drying of wood can not guarantee the quality of wood products, which has been the consensus of wood processing enterprises. Therefore, the investment of enterprises in drying equipment has increased significantly.
2. The main drying methods are conventional drying, dehumidification drying, solar drying, vacuum drying, high frequency drying, microwave drying, furnace gas drying and other drying methods coexist in a diversified pattern. Usually, wood drying monopoly enterprises mostly adopt large capacity conventional drying. The self-use drying chambers of wood processing enterprises vary in the choice of drying methods and the capacity of drying chambers, depending on the species, quantity, quality requirements and geographical location of the wood they dry.
3. The situation of centralized processing and centralized drying has taken shape initially. Because of the limitation of transportation cost and port city capacity, wood processing enterprises have settled in port cities or established raw material processing bases. This objectively formed a wood city of centralized processing and drying.
There are two ways to use microwave wood products drying equipment for wood drying, that is, to use microwave to quickly dry wood and to balance its moisture content by using the dielectric properties of wood. Microwave drying can prevent overdrying and make veneers softer. After drying, due to splitting or damage reduction, microwave drying veneers are less than hot air drying veneers. Microwave drying of wood may be used in the second stage of two-stage drying, that is, in the stage of low moisture content drying, which can give full play to its drying advantages and reduce energy consumption appropriately. The principle of microwave drying wood is that wet wood is used as dielectric, under the action of microwave electromagnetic field, water molecule polarization in wood is caused. At the same time, because of the frequent alternation of electromagnetic field, water molecule is high-speed.
According to the principle of microwave drying equipment heating, we can know that, unlike the traditional heating method, the heat diffusion of microwave heating is from inside to outside, not from outside to inside. The advantage of this heating method is that the heating process has no great relationship with the thickness of wood. In the internal vaporization process, the volume of heating will heat through along the thickness of wood at the same time, and the heat of heating will be transmitted. The gradient is consistent with the gradient of water content, and can dry wood in a short time. The traditional heating method, the exterior heating temperature is higher than the internal vaporization temperature, which not only causes the loss of heat, but also affects the use effect of the wood center because of the incomplete drying.
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