基于离散元法的螺旋进料器物料流动特性分析

Analysis on Flow Features for Screw Feeder Based on Discrete Element Model

针对附属于给定机型颗粒成型机上的螺旋进料器,对玉米秸秆粉料在进料器内的流动特性进行了模拟分析。利用离散元分析软件EDEM,创建了螺旋进料器部件的几何模型,并对玉米秸秆粉料颗粒接触模型和颗粒生成方法进行了研究,通过离散元模拟获得了现有工况下螺旋进料器工作时的粉料流动状态。采用HERTZ-MINDLIN无滑移接触模型,取重力加速度为9.81m·s^(-2),设置接触参数并生成了秸秆颗粒25000个进行仿真模拟。结果表明:在T=13.80~14.30s阶段为一典型的出料波动周期。出料过程中粉料呈浪涌流动状态的不连续脉动流;进一步分别针对颗粒密度、粒径大小、壁面摩擦因数、螺距、螺旋叶片内径参数进行了流态和速度的影响因素分析。颗粒密度分别取40,80,120kg·m^(-3)时,出料所需时间分别为21.37,17.68,15.01s;粒径分别取为2,1.8,1.6mm时,出料所需时间分别为17.68,18.06,19.37s;壁面静摩擦因数分别取为0.58,0.48,0.38时,出料所需时间分别为17.68,16.03,15.84s;螺旋叶片内径分别取为50,60,70mm时,在整个模拟时长20s内出料的平均流量分别为16.73,12.61,8.96g·s^(-1)。其中颗粒密度越大,粒径越大,则出料速度越快,但对粉料流态无明显影响;壁面摩擦因数越小、螺距越大、螺旋叶片内径越小,则出料口流速越快,流场分布越宽,落料范围越大,流态越剧烈。本研究可为适用于生物质颗粒成型机的螺旋进料器的设计和改进提供参考。

To investigate the flow of milled corn stover inside the screw feeder, which was attached to a specific pelletizer, the EDEM package was employed for its convenience in discrete element analysis, the geometric model of screw feeder was built,and the contact model among corn particles was given in this paper. The approaches for generating particles were also discussed,then the flow features of biomass material in screw feeder were acquired with DEM simulation. HERTZ-MINDLIN no-slide contact model was engaged, acceleration of gravity was set as 9.81m·s^-2, 25,000 straw particles were generated and simulated in given contact parameter. The results showed that the discontinuous biomass material flow fluctuated frequently. A typical outlet feeding wave was captured in T =13.80-14.30 s. The further analysis of flow state and velocity was conducted, the factors of particle density, particle size, wall friction coefficient and screw pitch as well as screw reamer inner diameter were analyzed individually. Particle density was 40, 80, 120kg·m^-3, elapsed time of feeding was 21.37 s, 17.68 s and 15.01 s, respectively; particle size was 2mm, 1.8mm and 1.6mm; elapsed time was 17.68 s, 18.06 s and 19.37 s respectively; wall friction coefficient was 0.58,0.48 and 0.38; elapsed time was 17.68 s,16.03 s and 15.84 s respectively; screw reamer inner diameter was 50 mm, 60 mm and70mm; average flow rate of feeding was 16.73g·s^-1, 12.61g·s^-1and 8.96g·s^-1in the 20 s simulation time. It turned out that the outlet velocity would be faster for the larger particle density and size, whereas the little impact was observed on powder flow.The smaller wall friction coefficient and screw reamer inner diameter, the larger screw pitch, would lead to faster outlet velocity and the wider falling area, and the flow appeared more violent. This work could provide some reference for the design and improvement of screw feeder with application to biomass pelletizer.