粉體熔融式凝聚機制與成長狀態; Granular Growth Mechanisms and Behaviors in Melt Agglomeration

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题名:	粉體熔融式凝聚機制與成長狀態;Granular Growth Mechanisms and Behaviors in Melt Agglomeration
作者:	鄭翔仁;Hsiang-Jen Cheng
贡献者:	機械工程研究所
关键词:	高剪力混合槽;成長形態;凝聚機制;黏著劑;成核;掃描式電子顯微鏡;潤濕特性;接觸角量測儀;異質性分布;同質性分布;scanning electron microscope;wetting property;heterogeneous dispersion;homogeneous dispersion;binder;granulation mechanism;growth behavior;high-shear mixer;nucleation;particle image velocimetry
日期:	2011-06-07
上传时间:	2012-01-05 12:27:33 (UTC+8)
摘要:	本論文以實驗的方式探討粉體物質添加黏著劑，受到水平與垂直雙葉片高剪力攪拌時，內部粉體的凝聚行為。探討主題包含凝聚機制、粉體速度場分布、成品外型、表面結構以及成長形態。首先建構濕式粉體凝聚設備--高剪力混合槽，用以操作所有基礎之凝聚現象。在碳酸鈣粉體低初始粒徑(32-75 μm)以及主葉片低轉速(300rpm)搭配下，粒徑分布隨操作時間呈現不同機制特性，包含成核、緊實或合併等現象，並進一步分析黏著劑黏度與含量的影響。其二以原凝聚設備，在碳酸鈣粉體高初始粒徑(75-150 μm)以及主葉片高轉速(500-700rpm)搭配下，配合影像處理技術和顆粒追蹤方法，觀察混合槽內混亂流場情況，並利用掃描式電子顯微鏡和成長機制的特性，深入探討不同粉體物質填充量對外型、結構和粒徑分布的影響。其三另外建構接觸角量測儀，用以觀察三種不同粉體物質:碳酸鈣、硫酸鈣和碳酸鈉在相同初始粒徑(75-150 μm)下，所受高溫黏著劑潤濕特性，進而應用潤濕特性觀察放入混合槽內凝聚狀態。由研究中發現粉體對黏著劑液體較慢潤濕的異質性分布現象，易促使誘入至高速凝聚大粒徑；而潤濕能力強之同質性分布現象則易導致零星的成核現象與小粒徑顆粒體。 The experimental methods were employed to investigate the granulation behavior of powder materials and binder liquid under the impeller and chopper mixing force. The main research topics include the granulation mechanisms, the velocity field of granules, the morphology of pellet, and the growth behaviors. The agglomeration equipment— a high-shear mixer was designed and prepared at first. The raw materials included calcium carbonate powders with an average particle size of 32-75 μm and been operated on low impeller speed (300 rpm). Three major agglomeration mechanisms are discussed in this study: nucleation, consolidation and coalescence. The influence of binder viscosity and content are further presented. The second research involved the effects of different initial volume fill ratios of the granulator on granular agglomeration. Calcium carbonate powders, with mean granule sizes of 75-150 μm were used as the raw material. Experiments of fill ratios are conducted for three conditions of parameters, (i) PEG 6000 and impeller speed at 500 rpm, (ii) PEG 6000 and impeller speed at 700 rpm, and (iii) PEG 4000 and impeller speed at 500 rpm. The range in granule size at the end of agglomeration increased as initial fill ratio increased. Low Vacuum Scanning Electron Microscope (LV-SEM) images of the surface structure of the granules are shown and the pellet shapes are also presented by the aspect ratio during the nucleation and final stages. On the other hand, the particle image velocimetry (PIV) experiments were also conducted by recording the moving granules during the mixing period with a high-speed Complementary Metal-Oxide-Semiconductor (CMOS) camera. The third research was to investigate the effects of the different surface properties of powders on granular agglomeration. Three different powders, with mean granule sizes of 75-150 μm were used as the raw material: calcium carbonate, calcium sulfate, and sodium carbonate. The wetting properties of the raw materials were measured with a contact angle instrument. The results indicate that the speed at which the droplets sink into the powder bed and the contact angle of binder droplets on the powder surface play important roles in determining the progress of the agglomeration process. Several types of agglomeration were found: a slurry state, only nucleation, snowballing, and induction growth behavior. The heterogeneity and homogeneity of the dispersion brought about by the coalescence, layering and slow-wetting behaviors were analyzed. A heterogeneous dispersion leads to induction behavior and subsequent growth, but a homogeneous dispersion leads to little or no nucleation and non-enlargement of size.
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