本文選題：非均一顆粒　切入點(diǎn)：氣固流動　出處：《清華大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：非均一顆粒在氣固流化床中的流動行為是流態(tài)化工程領(lǐng)域研究的熱點(diǎn)之一,也是數(shù)值模擬研究的難點(diǎn)。本文針對非均一顆粒的濃相氣固流動建立數(shù)值模型,研究顆粒的流動、擴(kuò)散和分層行為,并從微觀上剖析這類多相流動的氣固動力學(xué)特征和顆粒的運(yùn)動機(jī)制。這類流動涉及氣相、介質(zhì)顆粒和具有不同屬性的外加顆粒。鑒于該過程的復(fù)雜性,建模首先從只包含氣相和介質(zhì)顆粒的基礎(chǔ)氣固流動入手,分析對比現(xiàn)有的數(shù)值方法在模擬濃相氣固流動上的特征,研究其應(yīng)用于多相氣固流動的可行性。研究表明,目前的數(shù)值模擬方法可以在宏觀上準(zhǔn)確描述氣相、介質(zhì)顆粒的濃相氣固流態(tài)化過程,但同時考慮具有不同屬性的外加顆粒比較困難。因此,本文提出采用一種新的模型——TFM-DEM混合模型,來描述外加顆粒和介質(zhì)顆粒之間具有較大的密度和粒度差異的多元濃相氣固流動系統(tǒng)的流動行為。其中,采用TFM模型描述氣相和介質(zhì)顆粒的基礎(chǔ)氣固流動,而外加顆粒用DEM方法描述。通過實(shí)驗(yàn)研究了外加顆粒在濃相流化床中的分層行為,并驗(yàn)證了TFM-DEM混合模型的準(zhǔn)確性。以此為基礎(chǔ),采用TFM-DEM混合模型模擬研究了非均一顆粒在濃相流化床內(nèi)的流動行為,考察外加顆粒密度和粒度、以及一系列操作參數(shù)對顆粒流動行為的影響規(guī)律。研究得到的主要結(jié)論有:(1)外加顆粒在氣相-介質(zhì)顆粒濃相流化床內(nèi)按密度差異發(fā)生分層現(xiàn)象,但隨著外加顆粒粒度減小,外加顆粒的密度分層程度逐漸變差。當(dāng)外加顆粒粒度小至3 mm時,平均顆粒密度在1.9~2.2 g/cm3之間分布,此時流態(tài)化分選效果不佳。(2)通過顆粒受力分析發(fā)現(xiàn),外加顆粒懸浮主要依賴于床層靜壓梯度力,該靜壓梯度力大于輕組分顆粒的重力而小于重質(zhì)組分顆粒的重力,此差異推動了輕重顆粒的分離和分層。外加顆粒受到的介質(zhì)顆粒相曳力是它們無規(guī)則流動和混合主要動因。隨著外加顆粒粒度減小,氣相曳力和介質(zhì)顆粒相曳力所占的比例增加,受這些曳力的影響,細(xì)顆粒的流動軌跡與介質(zhì)相流動接近,因此分離很困難。(3)操作參數(shù)影響外加顆粒的分層質(zhì)量,其中介質(zhì)顆粒特性和流化風(fēng)速改變了床內(nèi)的流態(tài)化行為。床內(nèi)氣泡運(yùn)動和介質(zhì)顆粒的返混是造成外加顆�；旌系闹饕�,它們比床層密度變化對分層結(jié)果的影響更大。床內(nèi)的外加顆粒量和床高對外加顆粒的分層行為有類似的影響,提高床內(nèi)外加顆粒的數(shù)密度,可以改善外加顆粒的群體分層行為。
[Abstract]:The flow behavior of heterogeneous particles in a gas-solid fluidized bed is one of the hotspots in fluidization engineering and a difficult point in numerical simulation. In this paper, a numerical model of dense gas-solid flow of heterogeneous particles is established to study the flow of particles. Diffusion and stratification behavior, and microcosmic analysis of the gas-solid dynamics and the motion mechanism of such multiphase flows. These flows involve gaseous phase, medium particles and additional particles with different properties. Given the complexity of the process, The modeling begins with the basic gas-solid flow with only gaseous phase and medium particle, analyzes and compares the characteristics of the existing numerical methods in simulating the gas-solid flow of the dense phase, and studies the feasibility of its application to the multiphase gas-solid flow. The present numerical simulation method can accurately describe the gas-solid fluidization process of gas phase and medium particle macroscopically, but it is difficult to consider the addition particles with different properties at the same time. In this paper, a new model, TFM-Dem mixed model, is proposed to describe the flow behavior of a multicomponent dense phase gas-solid flow system with large density and particle size difference between the applied particles and the medium particles. The TFM model is used to describe the basic gas-solid flow of gas phase and medium particles, while the DEM method is used to describe the applied particles. The delamination behavior of the added particles in a dense phase fluidized bed is studied experimentally. The accuracy of TFM-DEM mixing model was verified. Based on this, the flow behavior of heterogeneous particles in a dense phase fluidized bed was simulated by TFM-DEM mixing model, and the particle density and particle size were investigated. The main conclusions of the study are as follows: (1) the separation of added particles in the gas-medium particle dense phase fluidized bed occurs according to the density difference, but with the decrease of the particle size, When the particle size is small to 3 mm, the average particle density is distributed in the range of 1.92g / cm ~ 3, and the fluidized separation effect is not good. The suspension of applied particles mainly depends on the static pressure gradient force of the bed, which is larger than the gravity of the light component particle but less than the gravity of the heavy component particle. This difference promotes the separation and stratification of heavy and heavy particles. The drag force of the medium particles subjected to the applied particles is the main cause of their irregular flow and mixing. The proportion of gas phase drag force and medium particle drag force increases. Due to these drag forces, the flow path of fine particle is close to that of medium phase flow, so it is very difficult to separate. The characteristics of medium particles and fluidization wind speed change the fluidization behavior in the bed. The bubble movement in the bed and the back mixing of the medium particles are the main reasons for the external particle mixing. The effect of the change of bed density on the stratification results is greater than that of the bed density, and the amount of particles in the bed and the bed height have similar effects on the stratification behavior of the added particles. Increasing the number density of the particles added inside and outside the bed can improve the population stratification behavior of the added particles.
【學(xué)位授予單位】：清華大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TQ051.13

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