基于EMMS結構的多尺度傳質反應模擬
發(fā)布時間：2018-09-11 13:57
【摘要】：氣固循環(huán)流化床反應器是一個流動、傳熱／傳質和反應多尺度時空耦合的復雜系統,其中介尺度流動結構(如團聚物或氣泡)起著關鍵性的作用�；诰鶆蚣僭O,忽略了亞網格介尺度結構影響的傳統雙流體模型(two-fluid model,TFM)對于模擬氣固非均勻流動反應體系是不合適的。需要在合理物理簡化的基礎上建立介尺度模型,才可準確描述流化床中的“三傳一反”行為。介尺度EMMS曳力模型在循環(huán)流化床流動模擬中已經得到了很好的應用,但其網格無關性還需進一步的驗證。同時,介尺度流動結構對于傳質和反應的影響也需進行考察。鑒于此,論文第二章首先研究了不同固相體積分率下的雙周期微元區(qū)域內,應用微元EMMS曳力和均勻曳力預測的滑移速度和傳質系數隨網格分辨率的變化。對于A類顆粒,微元EMMS曳力在不同固相體積分率下都表現出了更好的網格無關性。兩種曳力模型預測的流動結構隨網格細化都捕捉到更合理的非均勻流動結構,造成更大的傳質阻力,使得有效傳質系數下降,并在網格尺寸為10個顆粒直徑時趨于收斂。對于B類顆粒的傳質研究也發(fā)現了類似現象。細網格預測的有效傳質因子和基于EMMS結構的傳質非均勻因子隨固相體積分率的變化趨勢相同且在同一量級上。為了考慮介尺度非均勻結構對于傳質、反應的影響,論文第三章和第四章提出了基于EMMS結構的多流體傳質和反應模型,此模型在局部平衡或網格內沒有非均勻結構的假設時,可以退化為TFM框架下的傳質和反應模型。應用該模型分別在基于團聚物或氣泡的流動結構下分析傳質、反應過程,定義了反應和傳質的非均勻因子,以修正TFM傳質反應模型。論文通過二維和三維構體下的臭氧催化分解反應模擬,對模型進行了初步的驗證,模擬結果與文獻結果相符。反應速率越快,非均勻流動結構對于傳質和反應的影響越大。論文第五章通過虛擬實驗來考察計算中在線調節(jié)機械閥門和改變提升管懸浮段長度對于宏尺度非均勻流動行為的影響。首次實現了帶可調節(jié)機械閥的、三維全循環(huán)的循環(huán)流化床模擬,模擬結果和實驗描述相符。第六章對本論文進行了總結,提出了主要的結論和創(chuàng)新點,并對未來的研究進行了展望。
[Abstract]:Gas-solid circulating fluidized bed reactor (CFB) is a complex system with flow, heat / mass transfer and reaction multi-scale space-time coupling. Its mesoscale flow structure (such as agglomerates or bubbles) plays a key role. Based on the homogeneous hypothesis, the traditional two-fluid model (two-fluid model,TFM), which ignores the influence of mesoscale structure on subgrids, is not suitable for simulating gas-solid nonuniform flow systems. It is necessary to establish mesoscale model on the basis of reasonable physical simplification in order to accurately describe the behavior of "three to one inverse" in fluidized bed. Mesoscale EMMS drag model has been well applied in CFB flow simulation, but its mesh independence needs further verification. At the same time, the effect of mesoscale flow structure on mass transfer and reaction also needs to be investigated. In the second chapter, we first study the variation of slip velocity and mass transfer coefficient with grid resolution in the two-period microelement region with different volume fraction of solid phase, using differential EMMS drag and uniform drag force to predict slippage velocity and mass transfer coefficient. For A particles, the EMMS drag of microelement shows better mesh independence under different solid volume fraction. The flow structures predicted by the two drag models both capture more reasonable non-uniform flow structures with mesh refinement, resulting in greater mass transfer resistance, lower effective mass transfer coefficient, and convergence when the mesh size is 10 particle diameters. A similar phenomenon was found for the mass transfer of B particles. The effective mass transfer factor predicted by fine mesh and the non-uniform mass transfer factor based on EMMS structure have the same trend with solid volume fraction and are of the same order of magnitude. In order to consider the effect of mesoscale nonuniform structure on mass transfer and reaction, a multi-fluid mass transfer and reaction model based on EMMS structure is proposed in chapter 3 and chapter 4 in this paper. It can degenerate into mass transfer and reaction model under TFM framework. The model is used to analyze the mass transfer and reaction process under the flow structure of agglomerates or bubbles, and the heterogeneous factors of reaction and mass transfer are defined to modify the TFM mass transfer reaction model. In this paper, the ozone catalytic decomposition reaction is simulated under two and three dimensional structures, and the model is preliminarily verified. The simulation results are in agreement with the literature results. The faster the reaction rate, the greater the effect of heterogeneous flow structure on mass transfer and reaction. In the fifth chapter, the effect of on-line adjusting mechanical valve and changing the length of hoisting pipe on the macro-scale non-uniform flow behavior is investigated by virtual experiment. For the first time, a three-dimensional circulating fluidized bed simulation with adjustable mechanical valve is realized. The simulation results are in agreement with the experimental results. The sixth chapter summarizes the thesis, puts forward the main conclusions and innovations, and looks forward to the future research.
【學位授予單位】：中國科學院研究生院(過程工程研究所)
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TQ031
[Abstract]:Gas-solid circulating fluidized bed reactor (CFB) is a complex system with flow, heat / mass transfer and reaction multi-scale space-time coupling. Its mesoscale flow structure (such as agglomerates or bubbles) plays a key role. Based on the homogeneous hypothesis, the traditional two-fluid model (two-fluid model,TFM), which ignores the influence of mesoscale structure on subgrids, is not suitable for simulating gas-solid nonuniform flow systems. It is necessary to establish mesoscale model on the basis of reasonable physical simplification in order to accurately describe the behavior of "three to one inverse" in fluidized bed. Mesoscale EMMS drag model has been well applied in CFB flow simulation, but its mesh independence needs further verification. At the same time, the effect of mesoscale flow structure on mass transfer and reaction also needs to be investigated. In the second chapter, we first study the variation of slip velocity and mass transfer coefficient with grid resolution in the two-period microelement region with different volume fraction of solid phase, using differential EMMS drag and uniform drag force to predict slippage velocity and mass transfer coefficient. For A particles, the EMMS drag of microelement shows better mesh independence under different solid volume fraction. The flow structures predicted by the two drag models both capture more reasonable non-uniform flow structures with mesh refinement, resulting in greater mass transfer resistance, lower effective mass transfer coefficient, and convergence when the mesh size is 10 particle diameters. A similar phenomenon was found for the mass transfer of B particles. The effective mass transfer factor predicted by fine mesh and the non-uniform mass transfer factor based on EMMS structure have the same trend with solid volume fraction and are of the same order of magnitude. In order to consider the effect of mesoscale nonuniform structure on mass transfer and reaction, a multi-fluid mass transfer and reaction model based on EMMS structure is proposed in chapter 3 and chapter 4 in this paper. It can degenerate into mass transfer and reaction model under TFM framework. The model is used to analyze the mass transfer and reaction process under the flow structure of agglomerates or bubbles, and the heterogeneous factors of reaction and mass transfer are defined to modify the TFM mass transfer reaction model. In this paper, the ozone catalytic decomposition reaction is simulated under two and three dimensional structures, and the model is preliminarily verified. The simulation results are in agreement with the literature results. The faster the reaction rate, the greater the effect of heterogeneous flow structure on mass transfer and reaction. In the fifth chapter, the effect of on-line adjusting mechanical valve and changing the length of hoisting pipe on the macro-scale non-uniform flow behavior is investigated by virtual experiment. For the first time, a three-dimensional circulating fluidized bed simulation with adjustable mechanical valve is realized. The simulation results are in agreement with the experimental results. The sixth chapter summarizes the thesis, puts forward the main conclusions and innovations, and looks forward to the future research.
【學位授予單位】：中國科學院研究生院(過程工程研究所)
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TQ031
【相似文獻】
相關期刊論文 前10條
1 沈志恒;李巍;陸慧林;張慧芳;周全根;;不同曳力模型對提升管內氣固流動特性的影響[J];石油機械;2011年10期
2 歐陽潔,李靜海,崔俊芝;顆粒軌道模型中相間耦合關系及曳力計算的研究[J];動力工程;2004年06期
3 張晉;陳偉;;基于變尺度格子氣方法的氣固相間曳力模型[J];廣東化工;2012年07期
4 肖海濤,祁海鷹,由長福,徐旭常;循環(huán)流化床氣固曳力模型[J];計算物理;2003年01期
5 甘潔清;趙輝;楊朝合;山紅紅;;雙組分顆粒循環(huán)流化床中顆粒-顆粒曳力的比較[J];化工進展;2010年S1期
6 唐海;余徽;夏素蘭;賀西林;;液滴降落過程表面曳力及其形狀改變規(guī)律[J];化工設計;2007年03期
7 王嘉駿;顧雪萍;楊富軍;馮連芳;;雙流體模型中曳力及恢復系數對氣固流動的影響[J];高�；瘜W工程學報;2006年02期
8 李s，
本文編號：2236881
本文鏈接：http://sikaile.net/kejilunwen/huagong/2236881.html
