本文選題：攪拌槽　切入點：組合槳　出處：《南京理工大學》2015年碩士論文　論文類型：學位論文

【摘要】：本文選用聚醚多元醇(PPG)作為研究介質(zhì),采用數(shù)值模擬方法從宏觀和介觀兩個尺度對多層組合槳反應器進入了深入研究。并且初步探究攪拌槽內(nèi)存在的一種大尺度、低頻率的宏觀不穩(wěn)定現(xiàn)象,重點考察了攪拌轉(zhuǎn)速、槳葉類型、離底高度等因素對聚醚多元醇體系宏觀不穩(wěn)定頻率的影響,為反應器的優(yōu)化設(shè)計提供參考。1.對組合槳1(下層六葉半橢圓管渦輪槳+中層四寬葉翼型上提槳+上層四寬葉翼型上提槳)和組合槳2(下層六葉半橢圓管渦輪槳+中層六斜葉圓盤渦輪槳+上層六斜葉開啟式槳))攪拌釜內(nèi)液相PPG流場進行了計算流體力學(CFD)研究。結(jié)果表明,組合槳1中槳和上槳流體形成一個整體軸向循環(huán)有利于混合,組合槳2速度與湍流動能小于組合槳1。組合槳1更適用于聚醚多元醇體系的工業(yè)生產(chǎn)中。2.采用群平衡模型(PBM)與CFD相耦合的方法,研究多層組合槳攪拌槽內(nèi)空氣-PPG兩相混合的氣液傳質(zhì)特性,探究不同網(wǎng)格劃分對局部氣含率、氣泡直徑大小、傳質(zhì)系數(shù)的影響,結(jié)果表明,液相宏觀流場分布受到網(wǎng)格劃分影響,局部氣含率與氣泡直徑呈現(xiàn)雙峰分布,Grid 2總體氣含率模擬結(jié)果與實驗結(jié)果吻合較好。說明Grid 2網(wǎng)格劃分適用于聚醚多元醇-空氣體系的氣液混合,為進一步計算提供了參考。3.攪拌槽內(nèi)的流體的流動是非穩(wěn)態(tài)的,采用信號處理方法對攪拌槽內(nèi)宏觀不穩(wěn)定現(xiàn)象進行壓力信號分析,功率譜估計可以有效的分析低頻信號。結(jié)果表明,對于單層與雙層槳,宏觀不穩(wěn)定性頻率頻率主要分布在0.3-0.5Hz范圍內(nèi)。轉(zhuǎn)速增加,攪拌槽內(nèi)流體整體脈動增強,監(jiān)測點的位置對于宏觀不穩(wěn)定頻率近似無關(guān)。研究結(jié)果有助于了解流體混沌混合現(xiàn)象,避免攪拌槽內(nèi)機械勞損。
[Abstract]:In this paper, polyether polyol (PPG) was chosen as the research medium, and the numerical simulation method was used to study the multilayer combined paddle reactor from macroscopic and mesoscopic scales. The effects of stirring speed, blade type and bottom height on the macroscopic instability frequency of polyether polyol system were investigated. Reference for the optimal design of the reactor. 1. Combined propeller 1 (upper lift propeller with upper four wide blade airfoils of lower six-blade half elliptical tube turbine impeller) and combined propeller 2 (lower six-leaf semi-elliptical tube turbine propeller). The liquid phase PPG flow field of the upper hexagonal blade open propeller in the middle hexagonal disk turbine impeller has been studied by computational fluid dynamics (CFD). The results show that, An integral axial cycle of the fluid between the propeller and the upper propeller in the combined propeller 1 is favorable for mixing. The velocity and turbulent kinetic energy of combined propeller 2 are smaller than that of combined propeller 1.Combinatorial propeller 1 is more suitable for industrial production of polyether polyol system. The gas-liquid mass transfer characteristics of air-PPG two-phase mixing in a multi-layer combined propeller stirred tank are studied. The effects of different mesh generation on local gas holdup, bubble diameter and mass transfer coefficient are investigated. The distribution of macroscopic flow field in liquid phase is affected by meshing. The local gas holdup and bubble diameter show a bimodal distribution. The simulation results of total gas holdup are in good agreement with the experimental results. It shows that Grid _ 2 mesh is suitable for gas-liquid mixing of polyether polyol and air system. This paper provides a reference for further calculation. 3. The flow of fluid in stirred tank is unsteady. The pressure signal of macroscopic instability in agitating tank is analyzed by signal processing method. The power spectrum estimation can effectively analyze the low frequency signals. The results show that the frequency of macroscopic instability is mainly distributed in the range of 0.3-0.5Hz for single-layer and double-layer propellers, and the whole pulsation of the fluid in the stirred tank increases with the increase of the rotational speed. The location of the monitoring point is almost independent of the macroscopic unstable frequency. The results are helpful to understand the chaotic mixing phenomenon of the fluid and to avoid the mechanical strain in the mixing tank.
【學位授予單位】：南京理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ051.72

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本文編號：1580249