Temperature Distribution And Microstructure Changes Of The Poplar Wood During Microwave Processing

In this paper, the poplar wood is studied for the theoretical calculation and experiment test. For the theoretical calculation study, we build the three port feeding circular resonant cavity and the one feeding square resonant cavity based on the finite element analysis. The temperature distribution and penetration depth on different moisture content of wood by microwave have been studied. During the experiment test, the temperature distribution of different moisture content of wood has been studied using the microwave device of one feeding and two feeding resonant cavity. Meanwhile, we also study the interior structure of wood and compare change after microwave processing.The results indicate that:(1) Wood dimension, microwave frequency, heating time and moisture content have significant effects on the temperature distribution of the wood during microwave drying progress. When the radius of the wood is 0.8 times that of the circular cavity, the drying effect is optimal. Through the calculation, the length of the wood also affects the temperature variation coefficient which is less than 40.5% and energy efficiency which is more than 90% when the length is more than the height of waveguide. Meanwhile, at the same situation, the moisture content of wood is higher, the temperature distribution is more uniform. (2) Using the one port feeding resonant cavity microwave device, the moisture content of wood is lesser, the temperature distribution is more uniform. When the microwave device is the two port feeding resonant cavity, the moisture content of wood is higher, the temperature distribution is more uniform. Under the same situation, heating is more even using the two port feeding resonant cavity than one port. (3)Compared with the untreated wood, the interior structure of wood after microwave processing is destroyed seriously. The catheter suffer deformation and rupture, and the pit of wood is open. The structure of wood form a loose transverse and longitudinal interlinked network structure. It will speed up the migration of moisture content in wood and increase the permeability of wood. (4) The penetration depth is different with the moisture content wood. The moisture content of wood is higher, the depth is lesser.In conclusion, during the microwave heating process, the feeding model and wood size have significant effects on the temperature distribution of the wood. The uniformity of heating will improve enormously when the multi-port feeding and suitable heating time are used to the different moisture content.