【作者】 翟之平；

【导师】 王春光；

【作者基本信息】 内蒙古农业大学 ， 农业机械化工程， 2008， 博士

【摘要】 叶片式抛送装置由于具有结构简单、工作可靠、容易调整维修、输送能力强以及制造成本低等优点,因此应用范围非常广泛。叶片式抛送装置存在的主要问题是抛送功耗大,抛送效率低且容易堵塞。论文针对目前国内外对物料抛送机理研究中存在的不足,通过理论分析、计算机仿真模拟以及试验研究对物料的抛送机理进行了研究。在此基础上,对叶片式抛送装置的结构及运动参数进行了优化。(1)采用计算流体力学软件FLUENT对不同参数叶片式抛送装置的气流流场进行了三维数值模拟,获得了气流流场的基本特征。通过与气流流场试验研究结果比较表明,利用FLUENT对叶片式抛送装置气流流场进行模拟分析的结果是正确的。研究发现,气流流场的分布影响物料的抛送和所消耗功率,且抛送叶轮转速越高,出料直管处的气流速度越大,平均抛送距离越远。在此基础上,对抛送叶轮的叶片数、叶片倾角以及圆形外壳出口处的圆弧半径进行了优化。优化结果为:4叶片、圆形外壳、后倾10°叶片更有利于抛送,且出口处圆弧半径不宜太大。(2)采用理论分析、虚拟样机技术与高速摄像技术相结合的方法对物料沿抛送叶片的运动规律进行研究,获得了对物料抛送及所消耗功率起决定作用的物料抛出角和物料离开抛送叶片时速度的变化规律及影响因素,并得到物料的最佳抛出角范围为80o ~130o。建立了物料沿抛送叶片运动的ADAMS模型,为了综合考虑物料间的相互作用以及气流对物料的作用引入当量摩擦系数,通过与高速摄像试验数据进行回归分析计算得到当量摩擦系数的值,进而对ADAMS模型进行了修正。(3)通过高速摄像研究表明,在抛送叶片带动物料运动过程中,部分物料沿叶片滑移到叶片末端后离开叶片;另一部分物料沿叶片滑移了一段后就离开了叶片,在惯性及抛送叶轮内气流的作用下,沿圆形外壳出料口向出料直管运动,其中部分物料运动到出料口之前与下一叶片相遇,又被此叶片撞击、带动,直至运动到出料口。(4)为了降低抛送功耗,提高抛送效率,采用试验研究、理论分析与虚拟样机技术相结合的方法对所消耗功率进行了研究,对抛送叶轮的结构及运动参数进行了优化分析。建立了叶片式抛送装置所消耗功率、比功耗以及抛送效率表达式,并利用所修正的ADAMS模型对抛送叶轮结构及运动参数进行了优化。通过与试验结果进行比较分析,说明所修正的ADAMS模型及利用虚拟样机技术所进行的优化分析是可信的。结果表明:当叶轮外径为700mm,转速从650r/min增加到1050r/min(叶片末端线速度从25 m/s增加到40m/s),功耗及比功耗增加2~3倍;叶片前倾角从前倾5°增大到25°,比功耗增加5.5%~63.5%;叶片后倾角从后倾5°增大到25°,比功耗增加3.5%~12.7%,增加幅度较小;叶片为径向叶片且转速为650r/min时比功耗最小;径向叶片各转速的抛送效率范围为65%~69.5%,其中转速为950r/min时抛送效率最高。(5)为了获得物料流经出料直管及偏转弯管的运动规律,结合试验研究建立了物料流经出料直管的动力学模型,并在引用物料流经偏转弯管动力模型的基础上,利用MATLAB对其进行数值求解。为进一步优化出料直管及偏转弯管的结构参数奠定了基础。(6)对物料运动速度和相应位置的气流速度进行比较,发现从离开叶片到进入出料直管阶段,物料向上速度大于相应气流速度,物料主要靠叶片抛扔获得的能量来运动;进入出料直管后,物料向上速度小于相应气流速度,主要靠惯性和气流协助来输送物料。总之,物料主要靠叶片抛扔和气流辅助输送来抛送。(7)叶片后倾角为10°时比径向叶片的功耗增加了6.12%,而抛送距离增加了16.16%。实际生产中当不要求远距离抛送时,宜选径向叶片;当需远距离抛送时宜选后倾角为10°的叶片。(8)成功研制了叶片式抛送装置试验台,为研究抛送机理提供了试验设备。更多还原

【Abstract】 Impeller blowers are used widely to convey materials because of their simplicity, reliability, ease of maintenance and adjustment, high capacity and low manufacturing cost. However, they also have some negative problems such as excessive power consumption, inefficiency and even clogging in the process of blowing the materials. Given the existing deficiency of the throwing/blowing theory, the throwing/blowing mechanism of an impeller blower was studied through experiments, theory analysis and computer numerical simulation, and the parameter optimization of the impeller blower was finished in this paper.(1) The 3-D air flow in an impeller blower with different parameters was simulated and analyzed using CFD (computational fluid dynamics) software FLUENT, and the basic characteristics about the air field were gained. Comparing simulation results with experimental ones showed that the mathematical model was able to accurately simulate the actual air velocities. Moreover, Study results showed that the air flow pattern would affect the blowing efficiency and power consumption, and the higher the rotational speed of the impeller was, the higher the air flow velocity at a plane of the vertical pipe was, and the farther the straw-threw distance was. Furthermore, some main geometrical parameters, such as the numbers of the paddles, the mounting angle of the paddle, the shape of housing and the arc radius of its outlet etc, were optimized.(2) The movement laws of the chopped straws along paddles have been studied by means of theory analysis, virtual prototype and high speed photograph technology. The straw-threw angle at its optimal range was from 80 degree to 130 degree, and the velocity-changing laws that the straws left the paddles were obtained. The ADAMS simulation model of the chopped straws along paddles was established by the virtual prototype technology. Meanwhile, the movement trajectory of the chopped straws was photographed. Then the regression analysis on the data was carried out to determine the value of friction coefficient, and the ADAMS model was modified based on the value of friction coefficient.(3) From high speed photograph, we found that some straws moved along a paddle till the end of paddle; others left the paddle during their movement and moved towards outlet with the help of the air flow inside the impeller, some of them collided with another paddle which took them to the outlet.(4) To reduce the power consumption and improve the throwing/blowing efficiency, the power consumption was studied by experimenting, theoretical analyzing and virtual simulating. The mathematical equations for the power consumption, efficiency and specific power consumption of the impeller blower were set up. Moreover, the geometrical and kinematic parameters of the impeller were optimized based on modified ADAMS model. As was shown from the experiment results, the modified ADMAS model and the optimization results using virtual prototype technology were reliable. The results showed that the power and specific power consumption increased by 2-3 times as the rotation speed was increased from 650 to 1050r/min of the impeller (700mm in diameter). At the same time, the specific power consumption increased by 5.5%-63.5% when the forward angle of the paddle was increased from 5°to 25°; and it increased by 3.5%-12.7% when the backward angle of the paddle was increased from 5°to 25°. When paddles were radial arrangement and rotational speed was 650 rpm the specific power consumption was minimum.The throwing/blowing efficiency range for the radial paddle was 65%~69.5% at different rotational speeds and it reached the maximum at 950 rpm.(5) To gain basic kinematic characteristics of the chopped straws inside the vertical pipe and spout, the dynamic model of chopped straws moving upward in the vertical pipe has been established, and the dynamic equations were solved with MATLAB. It provided a reference for further optimizing the geometrical parameters of the vertical pipe and spout.(6) By comparing the straws velocity and air velocity at same position, it was shown that the upward velocity was bigger than the air velocity in the process of leaving the paddles and getting into the vertical pipe, and the energy of throwing straws comes from rotating paddles; After it got into the vertical pipe, the air velocity was bigger than the straw velocity, the straws were conveyed by means of inertia and air flow, the straws were conveyed mainly by means of the paddle throwing and the air blowing.(7) The study results showed that with paddles slanted 10°backward the impeller blower increased the specific power requirement by 6.12% and the throwing distance by 16.16% respectively compared to the impeller blower with radial paddles. Therefore, when required the long distance throwing, it was suitable to select the paddles with 10°backward, if throwing distance was not required, the radial paddles should be selected in the real production.(8) The experiment equipment of an impeller-blower were developed by ourselves.更多还原