| The demand of wood is more than the supply in China, which is a country with insufficient forest resources. Drying is the largest energy consumption in the process of wood processing, which taking up 40%-70% of the total energy consumption. How to improve the utilization rate, reduce the energy consumption and improve the quality of wood products has become an important issue in the research of wood science workers. Hot air drying kiln is the most widely used drying equipment in our wood processing enterprises. The cycling characteristics of air flow, especially the uniformity in the drying kiln is one of the most important factors affecting the drying quality, and also the main technical index to measure the performance of drying equipment. Therefore, it is significant to improve the performance of the wood drying equipment by improving the uniformity of air velocity in the drying kiln.First of all, according to the problem of the air flow disturbance, the air flow field distribution is not uniform, the jet is unable to control, one drying kiln can’t meet the drying of different tree species existing in conventional top-fan hot-air drying kiln, this study innovative designs the mobile adjustable jet device which composed of adjustable guide air cover and mobile automatic adjustment device; We can change the jet direction and air velocity by adjusting the baffle tongue position at adjustable guide air cover; at mobile automatic adjustment device, the driving motor drives the roller to rotate, this can achieve automatic regulation of fan support framework moving along the X direction; In this way, the flow range sent by the fan matches the distance between the fan and the vertical duct. With the combination of two sets of devices, the air flow can smoothly flow into the vertical air duct, to eliminate the air flow impacting, the vortex and other adverse factors, so that the horizontal air velocity through the plate stacking tends to uniform.Then,as the wood drying is a complicated and strongly coupled nonlinear dynamic sys tem, this paper uses Computational Fluid Dynamics(CFD) software SCT/Tetra to numerical simulation calculate the before and after optimization designed air flow field in the drying kiln, and analyze the characteristics of the air velocity in the drying kiln. Firstly, the conventional drying kiln and the after-optimization designed drying kiln have been simulated numerically when T40-II 5A type axial flow fan, blade angle 25 o, rated power 7450m3/h. By the comparative analysis of the velocity contours and monitoring point dates, the uniformity of air flow field distribution is increased by 72%. Secondly, when T40-II 5A type axial flow fan, blade angle 35 o, rated power 9090m3/h, in order to find the optimal matching distance between the air flow range sent by the fan and the vertical duct, and that between the fan and the vertical duct, we set five different fan air supply position along the X direction in the after optimization designed air drying kiln, and the drying kiln air flow field of the five different conditions has been simulated numerically. By the comparative analysis of velocity contours and monitoring point dates, the distance between the air flow range sent by the fan and the fan to the vertical duct matches best when the fan is set at point B, and it is the most uniform air flow field in the after-optimization designed air drying kiln.At last, Numerical simulation calculate the before and after optimization designed air flow field in the drying kiln, which not only verify the rationality of the design of mobile adjustable jet device, but also provide a reliable reference value for the design and process parameters of wood drying equipment in the future. |
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