本文關(guān)鍵詞： CFD 三維模型 破碎 微觀混合 RPB　出處：《北京化工大學》2016年博士論文　論文類型：學位論文

【摘要】：旋轉(zhuǎn)填充床反應器(Rotating Packed Bed,RPB)具有極強的過程強化性能和微觀混合性能,由于受到其內(nèi)部復雜填料結(jié)構(gòu)及觀測手段的限制,關(guān)于RPB的流體力學特征和混合行為的基礎研究相對較少。本文通過對RPB反應器內(nèi)部填料進行合理簡化,建立了三維RPB模型,分別在Design Modeler和Meshing-ICEM內(nèi)創(chuàng)建幾何模型和進行網(wǎng)格劃分,采用流體計算軟件ANSYSY (FLUENT)對液相在RPB內(nèi)的流體流動破碎過程和混合過程進行模擬研究。應用Realizable k-ε模型、VOF模型以及Sliding Meshes模型來計算反應器內(nèi)流體流動和氣-液兩相邊界。三維模擬結(jié)果可以清晰地顯示液體在整個反應器空間內(nèi)的分布及存在形態(tài)(孔流、液膜流動和液滴)。液體被旋轉(zhuǎn)填充床內(nèi)填料切割的過程,既有分散的過程,也有聚并的過程。填料轉(zhuǎn)速對液相顆粒大小及存在形態(tài)具有明顯影響,而進口速度對旋轉(zhuǎn)填充床空腔內(nèi)的液相顆粒大小影響不大。轉(zhuǎn)速、進液速度的增加和氣液接觸角的降低有利于提高液體的比表面積,進而有利于傳質(zhì)。液體停留時間隨著轉(zhuǎn)速和氣液接觸角的升高而降低。與二維模擬相比,三維模擬對液滴尺寸、液體速度和停留時間的描述更接近實際情況,模擬的液體尺寸和液體速度值更接近實驗值。由于VOF模型受網(wǎng)格大小制約,對于捕捉小尺寸液滴特別是小于最小網(wǎng)格數(shù)尺寸的液滴具有一定的缺陷,受計算機計算能力的限制,模擬得到的RPB內(nèi)子液滴尺寸分布具有一定的誤差。本文利用實驗和模擬結(jié)合的方法,通過實驗獲得液滴破碎信息,即得到不同尺寸液滴在絲網(wǎng)破碎的可能性、生成子液滴尺寸、撞擊位置對破碎的影響、聚集子液滴尺寸信息,把破碎信息編寫入Population Balance(PBM)方程中,得到了 RPB內(nèi)更合理的子液滴尺寸分布圖。這種方法同時可減小網(wǎng)格數(shù)降低計算時間,對于大尺寸反應器的模擬計算具有借鑒作用。另外,基于RPB內(nèi)流體流動的CFD模型,在穩(wěn)定流場內(nèi)添加液-液化學反應,模擬研究RPB的微觀混合效率。考察了氫離子轉(zhuǎn)化率、產(chǎn)物(H3BO3)、副產(chǎn)物(I2和I3-)以及離集指數(shù)在填料區(qū)徑向上的濃度分布。模擬結(jié)果表明:液-液反應過程和微觀混合過程主要是在距進口 10毫米以內(nèi)的區(qū)域(端效應區(qū))內(nèi)進行;各組分在RPB內(nèi)的分布、反應進程及微觀混合細節(jié)都能通過模擬結(jié)果得到清晰地顯示;轉(zhuǎn)速的增加能明顯強化RPB內(nèi)的微觀混合效應,這與前人實驗結(jié)果趨勢一致,且離集指數(shù)在相同填料徑向位置上與實驗值相差不大。本文運用CFD理論基礎建立了的簡化后的RPB模型,模擬研究了 RPB內(nèi)流體的流動、破碎特征以及微觀混合效率,這對RPB反應器的操作、放大以及優(yōu)化都能夠提供一定的指導和理論依據(jù)。
[Abstract]:Rotating Packed BedRPBs have strong process-strengthening and micro-mixing properties, due to the limitation of complex packing structure and observation methods. There are few basic studies on the hydrodynamic characteristics and mixing behavior of RPB. In this paper, the three-dimensional RPB model is established by reasonably simplifying the inner packing of RPB reactor, and the geometric model and meshing are created in Design Modeler and Meshing-ICEM, respectively. The fluid flow breakage and mixing process of liquid phase in RPB were simulated by ANSYSY fluent. The Realizable k- 蔚 model and Sliding Meshes model were used to calculate the fluid flow and gas-liquid two-phase boundary in the reactor. Boundary. Three-dimensional simulation results can clearly show the distribution and form of liquid in the whole reactor space (pore flow, Liquid film flow and droplet flow. The process of liquid cutting in a rotating packed bed involves both dispersion and aggregation. The filling speed has a significant effect on the size and morphology of liquid particles. However, the inlet velocity has little effect on the size of liquid particles in the cavity of rotating packed bed. The increase of rotational speed, the increase of liquid velocity and the decrease of gas-liquid contact angle can improve the specific surface area of liquid. The liquid residence time decreases with the increase of rotational speed and gas-liquid contact angle. Compared with the two-dimensional simulation, the three-dimensional simulation describes the droplet size, liquid velocity and residence time more closely to the actual situation. The simulated liquid size and liquid velocity value are closer to the experimental values. Because the VOF model is restricted by the mesh size, it has some defects in capturing small size droplets, especially those smaller than the minimum mesh size, and is limited by the computer computing ability. There is a certain error in the size distribution of the sub-droplet in the simulated RPB. In this paper, the breakage information of the droplet is obtained by using the method of combining experiment with simulation, that is, the possibility of the droplet breaking in the wire mesh with different sizes is obtained, and the size of the sub-droplet is generated. The effect of impact position on the breakage, the size information of the aggregator droplet is compiled into the Population balance Population equation, and a more reasonable distribution map of the sub-droplet size in the RPB is obtained. This method can also reduce the mesh number and reduce the calculation time. In addition, based on the CFD model of fluid flow in RPB, the micro-mixing efficiency of RPB was simulated by adding liquid-liquid chemical reaction in the steady flow field, and the conversion of hydrogen ions was investigated. The concentration distribution of H3BO3, by-products I2 and I3-) and the separation index in the radial packing region. The simulation results show that the liquid-liquid reaction process and the microscopic mixing process are mainly carried out in the region (end effect zone) less than 10 mm from the inlet. The distribution of each component in RPB, reaction process and microscopic mixing details can be clearly displayed by simulation results, and the increase of rotational speed can obviously strengthen the microscopic mixing effect in RPB, which is consistent with the previous experimental results. In this paper, the simplified RPB model based on CFD theory is used to simulate the flow, fracture characteristics and microscopic mixing efficiency of the fluid in RPB. This can provide some guidance and theoretical basis for the operation, amplification and optimization of RPB reactor.
【學位授予單位】：北京化工大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TQ021.4

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