【摘要】：本文針對(duì)一種表面吸氣式長(zhǎng)槳短葉片復(fù)合攪拌器(LSB攪拌槳),采用實(shí)驗(yàn)研究與數(shù)值模擬相結(jié)合的方法,對(duì)該LSB槳在平底攪拌釜內(nèi)的自吸氣過程及氣液分散特性進(jìn)行研究。分別考察了操作條件及攪拌釜結(jié)構(gòu)參數(shù),如液位高度、擋板到釜壁的距離、液體性質(zhì)、反應(yīng)釜的幾何尺寸等,對(duì)臨界攪拌轉(zhuǎn)速(NC)的影響,并對(duì)攪拌釜內(nèi)氣泡大小及其分布進(jìn)行測(cè)量與分析。首先,用觀察法對(duì)臨界攪拌轉(zhuǎn)速進(jìn)行定義,當(dāng)固定釜底間隙(C/T= 0.25),液位高度變化范圍為H/T=0.5-1.8時(shí),長(zhǎng)槳(LBs)為部分浸沒,結(jié)果表明,隨著液位的升高,NC先降低后升高最后趨于定值,且在H/T=1.0左右出現(xiàn)最小值。這是由于在液位較低時(shí),短葉片(SBs)距離液面較近,短葉片對(duì)表面吸氣起著重要作用;在液位較高時(shí),短葉片對(duì)表面吸氣的影響可忽略,長(zhǎng)槳控制著表面吸氣。針對(duì)具有不同尺寸的攪拌釜(T= 200mm,400 mm,600 mm),測(cè)量了不同液位下的NC,將NC與臨界葉端速度進(jìn)行關(guān)聯(lián)(Utip,c=πDLNC),結(jié)果表明,當(dāng)攪拌槳的特征尺寸DL180mm時(shí),utip,c隨著DL的增加而增加,當(dāng)DL達(dá)到180mm后,DL對(duì)Utip,c的影響較小,Utip,c趨于定值(Utip,c= 0.61 m/s)。其次,采用大渦模擬(LES)耦合流體體積法(VOF)對(duì)攪拌釜內(nèi)表面吸氣過程進(jìn)行數(shù)值模擬。分別從液面波動(dòng)、靜壓分布、湍渦分布、速度場(chǎng)分布及吸氣過程對(duì)表面臨界吸氣現(xiàn)象進(jìn)行分析,數(shù)值模擬結(jié)果表明,當(dāng)長(zhǎng)槳在液體表面劃過后,氣液接觸面處的液相軸向平均速度(uz)和軸向脈動(dòng)速度(uz,rms)在徑向范圍(0.4r/R0.5)內(nèi)出現(xiàn)最大值(uz,max≈0.5 m/s,uz,rms,max≈0.0/s),證明了在長(zhǎng)槳背水面形成液體凹陷區(qū),隨后凹陷區(qū)上方的液體回填,將氣體卷吸入液下。最后,建立了照相法測(cè)量氣液兩相流氣泡大小及其分布的方法,對(duì)LSB攪拌釜內(nèi)氣-液分散特性進(jìn)行實(shí)驗(yàn)研究,所得圖像通過自主開發(fā)的圖像處理軟件進(jìn)行處理。分別采用Canny算子與Sobel算子進(jìn)行氣泡識(shí)別與邊緣檢測(cè),發(fā)現(xiàn)采用Canny算子得到的氣泡分布與實(shí)驗(yàn)結(jié)果較為吻合。從實(shí)驗(yàn)結(jié)果來看,當(dāng)LSB攪拌槳的轉(zhuǎn)速N= 100rpm～140rpm時(shí),釜內(nèi)氣泡的直徑約為0.5mm～6mm,且隨著攪拌轉(zhuǎn)速增加,氣泡直徑分布趨于均一。
[Abstract]:In this paper, the self-inspiratory process and gas-liquid dispersion characteristics of the LSB impeller in a flat-bottom agitator are studied by means of experimental study and numerical simulation, aiming at a surface suction type long propeller and short blade composite agitator (LSB agitator). The effects of operating conditions and structural parameters of agitator, such as the height of liquid level, the distance from the baffle to the wall of the reactor, the liquid properties, the geometry of the reactor and so on, on the critical stirring speed (NC) were investigated. The size and distribution of bubbles in agitator were measured and analyzed. First of all, the critical stirring speed is defined by observation method. When the fixed bottom clearance (C / T = 0.25) and the liquid level height range is H/T=0.5-1.8, the (LBs) of the long propeller is partially immersed. The results show that, With the increase of the liquid level, the NC decreases first, then increases to a fixed value, and the minimum value appears around H/T=1.0. This is because when the liquid level is low, the short blade (SBs) is close to the liquid surface, and the short blade plays an important role in the surface suction, while at the higher liquid level, the influence of the short blade on the surface suction is negligible, and the long blade controls the surface suction. For a stirred tank with different sizes (T = 200mm / 400 mm,600 mm), NC, at different liquid levels was measured to correlate NC with critical vane end velocity (Utip,c= 蟺 DLNC), results show that when the characteristic size of the agitator is DL180mm, utip,) C increased with the increase of DL. When DL reached 180mm, DL had little effect on Utip,c, and Utip,c tended to be fixed (Utip,c= 0.61 m / s). Secondly, the large eddy simulation (LES) coupled fluid volume method (VOF) is used to simulate the suction process on the inner surface of the stirred tank. The critical inspiratory phenomena on the surface are analyzed from surface wave, static pressure distribution, turbulent vortex distribution, velocity field distribution and suction process, respectively. The numerical simulation results show that when the propeller is drawn on the liquid surface, The axial average velocity (uz) and the axial pulsation velocity (uz,rms) of the liquid phase at the gas-liquid interface are maximum in the radial range (0.4r/R0.5) (uz,max 鈮，

本文編號(hào)：2326289