【摘要】：顆粒物料在生產(chǎn)操作和生活活動(dòng)中隨處可見,而且是經(jīng)濟(jì)建設(shè)過程中不可或缺的材料。顆粒物料的存儲(chǔ)、運(yùn)輸及使用等操作過程經(jīng)常見到顆粒物料自由下落的現(xiàn)象,自由下落的顆粒物料會(huì)逃逸到空氣中,造成局部甚至大面積的環(huán)境污染。粉塵進(jìn)入空氣會(huì)引發(fā)一系列的環(huán)境問題,在生產(chǎn)過程中產(chǎn)生的顆粒危害工作人員的身體健康、破壞生產(chǎn)設(shè)備、影響產(chǎn)品質(zhì)量,顆粒物積累到一定濃度還可能引發(fā)塵爆;大量的顆粒物進(jìn)入環(huán)境空氣中造成大范圍的污染,近些年我國(guó)北方城市頻頻出現(xiàn)的霧霾天氣就與顆粒物大量進(jìn)入空氣有關(guān)。顆粒物料自由下落后與壁面接觸反彈過程會(huì)引起二次揚(yáng)塵,使顆粒揚(yáng)塵的污染面積變大;下落物料對(duì)堆料形成的沖擊也會(huì)引起二次揚(yáng)塵。本論文在前人對(duì)氣固兩相流動(dòng)研究的基礎(chǔ)上,通過對(duì)氣固兩相流動(dòng)運(yùn)動(dòng)規(guī)律的分析,掌握顆粒物料在空氣中的運(yùn)動(dòng)規(guī)律,為控制顆粒物料自由下落引起的揚(yáng)塵奠定基礎(chǔ),并對(duì)顆粒反彈和堆積過程進(jìn)行數(shù)值模擬研究。本學(xué)位論文對(duì)圓球形、均一粒徑的顆粒物料下落過程、反彈遷移過程和堆積過程的研究主要采用數(shù)值模擬的方法,利用基于有限元方法的流體計(jì)算軟件COMSOL Multiphysics 5.0。針對(duì)物料下落的不同過程采用不同的物理模塊來(lái)進(jìn)行計(jì)算,主要用到湍流模塊、流體流動(dòng)粒子追蹤模塊以及動(dòng)網(wǎng)格模塊。在模擬研究中,引入基于曳力方程的流體與顆粒之間的相互作用力,在標(biāo)準(zhǔn)_(k-e)湍流模型中采用歐拉—拉格朗日方法研究,實(shí)現(xiàn)了流體相與顆粒相兩相間的雙向耦合,并通過對(duì)流體速度變化和顆粒速度變化的分析驗(yàn)證了本文雙向耦合模擬氣固兩相流動(dòng)的正確性;本文是運(yùn)用克努森余弦定律和蒙特卡洛方法,進(jìn)行了考慮顆粒與壁面碰撞后動(dòng)量損失的隨機(jī)反彈遷移過程的模擬;在對(duì)顆粒堆積過程的研究中提出通過網(wǎng)格變形來(lái)反映顆粒堆積的過程,在該方法中通過引入累加器作為中間變量將與下壁面接觸顆粒的量轉(zhuǎn)化為網(wǎng)格變形的量,最終通過網(wǎng)格的變形的形態(tài)反映顆粒堆積后的形態(tài);同時(shí)觀察了顆粒堆積后對(duì)流場(chǎng)流動(dòng)的影響情況。模擬結(jié)果表明:顆粒粒徑越大、下落高度越高、密度越大對(duì)流體的擾動(dòng)也越大,同時(shí)顆粒群中的顆粒受到流體的影響比單顆粒大而且更加復(fù)雜,并不是顆粒數(shù)目簡(jiǎn)單相加的結(jié)果;顆粒反彈過程的模擬實(shí)現(xiàn)了考慮動(dòng)量損失以及反彈后方向的隨機(jī)的情況。雖然通過網(wǎng)格變形來(lái)反映顆粒的堆積取得了理想的結(jié)果,但與真實(shí)的顆粒堆積過程相比仍有差異。通過對(duì)比分析顆粒堆積與不堆積的流場(chǎng)速度變化情況,得出在研究顆粒二次揚(yáng)塵問題時(shí)不可忽略顆粒堆積的影響。
[Abstract]:Granular materials can be found everywhere in production operation and daily activities, and they are indispensable materials in economic construction. In the process of storage, transportation and use of granular materials, the phenomenon of free drop of particle materials is often observed. The free falling particles will escape into the air, resulting in local or even large-scale environmental pollution. Dust entering the air will cause a series of environmental problems, the particles produced in the production process harm the health of workers, damage production equipment, affect the quality of products, particulate matter accumulation to a certain concentration may also lead to dust explosion; A large number of particles enter the ambient air and cause a wide range of pollution. In recent years, the frequent occurrence of haze weather in the northern cities of China is related to the large amount of particulate matter entering the air. The secondary dust will be caused by the contact with the wall after free falling of the particle material, and the pollution area of the particle dust will become larger, and the impact of the falling material on the formation of the pile material will also cause the secondary dust. On the basis of previous researches on gas-solid two-phase flow, through the analysis of gas-solid two-phase flow law, this paper grasps the movement law of particle material in air, and lays a foundation for controlling the dust caused by the free falling of particle material. The process of particle rebound and accumulation is studied numerically. In this dissertation, numerical simulation is used to study the falling process, rebound migration process and stacking process of spherical and homogeneous particles, and the fluid calculation software COMSOL Multiphysics 5.0 based on finite element method is used. Different physical modules are used to calculate the different processes of material falling, including turbulence module, fluid flow particle tracing module and moving mesh module. In the simulation study, the interaction force between fluid and particle is introduced based on the drag equation, and the Euler-Lagrange method is used in the standard _ (k-e) turbulence model to realize the bidirectional coupling between the fluid phase and the particle phase. The bidirectional coupling simulation of gas-solid two-phase flow is verified by the analysis of fluid velocity and particle velocity. In this paper, using Knudsen's cosine law and Monte Carlo method, the stochastic rebound migration process considering momentum loss after particle collision with wall is simulated. In the study of particle stacking process, the mesh deformation is proposed to reflect the particle stacking process. In this method, the amount of particles in contact with the lower wall is transformed into the mesh deformation by introducing an accumulator as an intermediate variable. Finally, the shape of the deformation of the mesh reflects the shape of the particles after the accumulation; At the same time, the influence of the flow in the flow field after the accumulation of particles was observed. The simulation results show that the larger the particle size, the higher the falling height, and the greater the density, the greater the disturbance to the fluid, and the more complex the influence of the particles in the particle group is than that of the single particle. It is not the result of simple addition of particle number; The simulation results show that the momentum loss and the direction after the rebound are considered randomly. Although the ideal results can be obtained by using mesh deformation to reflect the accumulation of particles, there is still a difference compared with the real process of particle stacking. By comparing and analyzing the velocity variation of particle accumulation and non-accumulation, it is concluded that the influence of particle accumulation should not be ignored in the study of particle secondary hoisting.
【學(xué)位授予單位】：西安建筑科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：X513

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本文編號(hào)：2361047