氣固下行床能量最小多尺度（EMMS）模型
發(fā)布時間：2018-10-18 06:43
【摘要】：氣固下行床是典型的非線性、非平衡系統(tǒng),呈現(xiàn)出時空多尺度結(jié)構(gòu)。與快速流化床類似,氣固下行床中也存在顆粒團聚現(xiàn)象。由于能量最小多尺度(EMMS)理論考慮了系統(tǒng)中的多尺度非均勻結(jié)構(gòu),能較好地描述氣固兩相流中非均勻流動結(jié)構(gòu)特征,因而在循環(huán)流化床中得到了廣泛的應(yīng)用和發(fā)展。本文擬將EMMS理論進一步擴展應(yīng)用于氣固下行床中,以建立并流和逆流下行床的軸向一維模型來探究其流體力學(xué)參數(shù)的軸向分布特征。將氣固并流下行床多尺度分解為稀相、密相和相互作用相,并用稀密兩相及相間的10個流動結(jié)構(gòu)參數(shù)來描述,并進一步建立多尺度質(zhì)量和動量守恒方程。根據(jù)氣固兩相流競爭性協(xié)調(diào)原理,建立了氣固并流任意軸向不同發(fā)展階段的截面穩(wěn)定性條件,并用統(tǒng)一的數(shù)學(xué)形式進行了表達。通過用局部穩(wěn)定性條件來優(yōu)化團聚物數(shù)密度的方法確定聚團尺寸,不需要引入團聚物經(jīng)驗關(guān)聯(lián)式就可對并流下行床軸向一維模型進行數(shù)值求解。對模型計算結(jié)果的定性分析以及和實驗數(shù)據(jù)的定量比較均表明該模型能成功的描述并流下行床軸向宏觀流體動力學(xué)特征,并可望適用于從細顆粒到粗顆粒的不同氣固系統(tǒng)。考慮氣固逆流與并流下行床中氣固兩相流動機制以及顆粒團聚機理的異同,采用與建立并流下行床軸向一維模型相同的方法,依次對氣固逆流下行床系統(tǒng)進行多尺度分解,建立相應(yīng)的本構(gòu)方程,分析截面穩(wěn)定性條件,并利用團聚物數(shù)密度優(yōu)化的方法進行數(shù)值求解。但逆流下行床一維模型的計算結(jié)果受經(jīng)驗性參數(shù)壁面摩擦力的影響較大,因此在模型使用過程中需要對此參數(shù)進行合理估計,以保證模型預(yù)測的準(zhǔn)確性。氣固并流和逆流下行床EMMS模型由于考慮了氣固兩相流中的多尺度相互作用,因而具有一定的普適性。該研究豐富了基于EMMS的復(fù)雜氣固系統(tǒng)全循環(huán)穩(wěn)態(tài)建模理論,從而為實現(xiàn)以工業(yè)過程的實時模擬為特征的化工虛擬過程奠定基礎(chǔ)。
[Abstract]:Gas-solid downcomer is a typical nonlinear, non-equilibrium system with a multi-scale structure in time and space. Similar to the fast fluidized bed, particle agglomeration also exists in the gas-solid downflow bed. Because the energy minimization multi-scale (EMMS) theory considers the multi-scale non-uniform structure in the system and can describe the non-uniform flow structure of gas-solid two-phase flow, it has been widely used and developed in circulating fluidized bed (CFB). In this paper, the EMMS theory is further extended to the gas-solid downflow bed, in order to establish the axial one-dimensional model of the parallel flow and countercurrent downflow to study the axial distribution characteristics of its hydrodynamic parameters. In this paper, the gas / solid flow downstream bed is decomposed into rarefied phase, dense phase and interaction phase, and the multi-scale mass and momentum conservation equations are further established by using 10 flow structure parameters of dilute dense two-phase and interphase flow. According to the principle of competitive coordination of gas-solid two-phase flow, the cross-section stability conditions of gas-solid flow in different development stages in arbitrary axial direction are established and expressed in a unified mathematical form. By using the local stability condition to optimize the number density of agglomerates to determine the size of the agglomerates, the axial one-dimensional model of the shunt downlink bed can be solved numerically without introducing an empirical correlation of the aggregates. The qualitative analysis of the model results and the quantitative comparison with the experimental data show that the model can successfully describe the axial macrohydrodynamic characteristics of parallel flow downflow beds and is expected to be suitable for different gas-solid systems from fine particles to coarse particles. Considering the similarities and differences of gas-solid two-phase flow mechanism and particle agglomeration mechanism between gas-solid countercurrent and co-current downflow, the multi-scale decomposition of gas-solid countercurrent downflow system is carried out by using the same method as establishing one dimensional axial model of co-current downflow. The corresponding constitutive equation was established and the stability condition of the section was analyzed. The numerical solution was carried out by using the method of optimization of aggregate number density. However, the results of one-dimensional countercurrent downflow model are greatly affected by the empirical parameter wall friction, so it is necessary to estimate this parameter reasonably in order to ensure the accuracy of the model prediction. The EMMS model of gas-solid parallel flow and countercurrent downflow has a certain universality because of the consideration of the multi-scale interaction in gas-solid two-phase flow. The research enriches the modeling theory of complete cycle steady state of complex gas-solid system based on EMMS, thus laying a foundation for realizing the chemical virtual process characterized by real-time simulation of industrial process.
【學(xué)位授予單位】：中國石油大學(xué)(華東)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TQ051.1
本文編號：2278315
[Abstract]:Gas-solid downcomer is a typical nonlinear, non-equilibrium system with a multi-scale structure in time and space. Similar to the fast fluidized bed, particle agglomeration also exists in the gas-solid downflow bed. Because the energy minimization multi-scale (EMMS) theory considers the multi-scale non-uniform structure in the system and can describe the non-uniform flow structure of gas-solid two-phase flow, it has been widely used and developed in circulating fluidized bed (CFB). In this paper, the EMMS theory is further extended to the gas-solid downflow bed, in order to establish the axial one-dimensional model of the parallel flow and countercurrent downflow to study the axial distribution characteristics of its hydrodynamic parameters. In this paper, the gas / solid flow downstream bed is decomposed into rarefied phase, dense phase and interaction phase, and the multi-scale mass and momentum conservation equations are further established by using 10 flow structure parameters of dilute dense two-phase and interphase flow. According to the principle of competitive coordination of gas-solid two-phase flow, the cross-section stability conditions of gas-solid flow in different development stages in arbitrary axial direction are established and expressed in a unified mathematical form. By using the local stability condition to optimize the number density of agglomerates to determine the size of the agglomerates, the axial one-dimensional model of the shunt downlink bed can be solved numerically without introducing an empirical correlation of the aggregates. The qualitative analysis of the model results and the quantitative comparison with the experimental data show that the model can successfully describe the axial macrohydrodynamic characteristics of parallel flow downflow beds and is expected to be suitable for different gas-solid systems from fine particles to coarse particles. Considering the similarities and differences of gas-solid two-phase flow mechanism and particle agglomeration mechanism between gas-solid countercurrent and co-current downflow, the multi-scale decomposition of gas-solid countercurrent downflow system is carried out by using the same method as establishing one dimensional axial model of co-current downflow. The corresponding constitutive equation was established and the stability condition of the section was analyzed. The numerical solution was carried out by using the method of optimization of aggregate number density. However, the results of one-dimensional countercurrent downflow model are greatly affected by the empirical parameter wall friction, so it is necessary to estimate this parameter reasonably in order to ensure the accuracy of the model prediction. The EMMS model of gas-solid parallel flow and countercurrent downflow has a certain universality because of the consideration of the multi-scale interaction in gas-solid two-phase flow. The research enriches the modeling theory of complete cycle steady state of complex gas-solid system based on EMMS, thus laying a foundation for realizing the chemical virtual process characterized by real-time simulation of industrial process.
【學(xué)位授予單位】：中國石油大學(xué)(華東)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TQ051.1
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