硬球—擬顆�！浨蝰詈夏M及其化工應用
發(fā)布時間：2018-08-17 19:57
【摘要】：納微流動與傳遞過程廣泛存在于化學工程領域,諸如多相介質(zhì)的界面、催化劑顆粒中的多級孔道和微化工系統(tǒng)等。隨著對化工工藝和設備精準設計與調(diào)控要求的不斷提高,認識這些過程的機理變得越發(fā)重要。在納微尺度,對動態(tài)過程的全面實驗研究還存在諸多困難,而傳統(tǒng)的連續(xù)介質(zhì)模擬方法隨著系統(tǒng)特征努森數(shù)的增大逐漸失效。在該尺度下,流體更多地表現(xiàn)出分子的離散性質(zhì),因此各種離散粒子方法的應用近年來受到廣泛重視,但其計算速度與精度之間的矛盾一直沒有很好地解決。為此,本論文通過不同離散粒子方法的耦合建立了一套能夠從微觀水平高效準確地模擬納微尺度或其他高努森數(shù)條件下氣體流動、擴散和反應過程的模型和算法框架。論文的主要內(nèi)容如下：緒論部分分析了軟球、硬球、擬顆粒和直接模擬蒙特卡洛等典型的離散粒子模擬方法及其各自的優(yōu)缺點以及前人在耦合不同模型方面的工作,據(jù)此提出了本論文的研究思路。即：以嚴格的軟球模型(或其組合)模擬稠密或接近界面的復雜過程,而以簡化的硬球模型(或其組合)模擬稀薄和遠離壁面的條件下氣體的流動與擴散過程,而以結合兩者優(yōu)勢的擬顆粒模擬提供其過渡以及硬球并行模擬中局部的近似。第二章首先改進了事件驅動的硬球模擬與時間驅動的擬顆粒模擬的耦合與并行方法,嚴格確定了硬球與擬顆粒物性間的轉換關系,并在管內(nèi)流動和擴散模擬中驗證了其正確性,表明了該耦合能有效克服硬球模擬擴展性差和擬顆粒模擬對稀薄氣體效率低的問題,實現(xiàn)高效準確的大規(guī)模并行模擬。該方法還成功應用于氣體在納微孔道內(nèi)的非平衡擴散以及在復雜多孔介質(zhì)內(nèi)的擴散研究,表明了其在微化工過程和催化劑開發(fā)等方面實際應用的可行性。另外,應用該方法還初步開展了高超聲速流動的模擬,說明了其在航天航空等其他領域的潛在應用價值。第三章從算法改進和并行優(yōu)化兩方面深入研究了軟球模擬方法,創(chuàng)新提出了關于粒子搜索的多殼層鄰居列表算法。該算法通過對粒子跨越各殼層可能性的簡單預估,有效提高了搜索效率。在此基礎上,發(fā)展了針對軟球模擬的多線程和向量化并行、眾核與多核處理器協(xié)同、計算／通信／存取重疊等方法,建立了一套高效的大規(guī)模并行程序�；谏鲜龉ぷ�,第四章最終實現(xiàn)了軟球、硬球和擬顆粒模擬三者的耦合。論文導出了軟球與擬顆粒模型間的參數(shù)轉換關系,提出了采用不同模型的區(qū)域間通用的連接模式,在保持軟球區(qū)域外部有擬顆粒過渡層的條件下,可構建任意復雜的界面。論文還為耦合模擬建立了簡單幾何體和固定粒子等多種邊界條件,提高了方法的實用性。論文還通過經(jīng)典的管流模擬等驗證了該方法的正確性。第五章應用上述耦合模擬方法通過簡單的概念模型研究了氣固界面反應中界面結構對擴散和反應過程的影響。研究發(fā)現(xiàn),在給定的反應條件下,由于擴散和反應過程在不同條件下相互影響的不同方式,界面結構存在最有利于整體反應速率的特定形狀參數(shù)。通過建立更真實與細致的反應物及界面模型,該耦合方法有望提供諸如催化劑孔道結構設計等方面的機理分析與優(yōu)化工具。第六章概括了論文的主要結論和創(chuàng)新點,并展望了后續(xù)工作。
[Abstract]:Nano-micro flow and transfer processes exist widely in chemical engineering, such as the interface of multiphase media, multistage channels in catalyst particles, and micro-chemical systems. With the increasing requirements for precise design and control of chemical processes and equipment, it becomes more and more important to understand the mechanism of these processes. At nano-micro scale, dynamic processes are becoming more and more important. There are still many difficulties in the comprehensive experimental study, but the traditional continuum simulation method gradually fails with the increase of the system characteristic Knudsen number. At this scale, fluids show more discrete properties of molecules, so the application of various discrete particle methods has been widely valued in recent years, but there is a contradiction between the calculation speed and accuracy. The main contents of this paper are as follows: In the introduction part, the soft sphere and the hard sphere are analyzed. Some typical discrete particle simulation methods, such as sphere, quasi-particle and direct simulation Monte Carlo, and their respective advantages and disadvantages, as well as the previous work on coupling different models, are proposed in this paper. That is, the rigid soft sphere model (or its combination) is used to simulate the complex process of dense or close to the interface, while the hard sphere is simplified. The model (or its combination) simulates the gas flow and diffusion processes in thin and far-from-the-wall conditions, and provides the transition and local approximation in the hard-sphere parallel simulation by combining the advantages of both quasi-particle simulation. In Chapter 2, the coupling and parallel methods of event-driven hard-sphere simulation and time-driven quasi-particle simulation are improved. The conversion relationship between hard sphere and pseudo-particulate matter is strictly determined, and its correctness is verified in the simulation of flow and diffusion in pipe. The results show that the coupling can effectively overcome the problems of poor expansibility of hard sphere simulation and low efficiency of pseudo-particulate simulation for rarefied gas, and realize efficient and accurate large-scale parallel simulation. The non-equilibrium diffusion in nano-microporous channels and the diffusion in complex porous media show the feasibility of its practical application in micro-chemical process and catalyst development. In the third chapter, the soft sphere simulation method is deeply studied from two aspects of algorithm improvement and parallel optimization, and the multi-shell neighbor list algorithm about particle search is innovatively put forward.The algorithm effectively improves the search efficiency by simply predicting the possibility of particles crossing each shell.On this basis, the multi-threading and direction of soft sphere simulation are developed. Based on the above work, Chapter 4 finally realizes the coupling of soft-sphere, hard-sphere and quasi-granular simulation. The paper derives the parameter transformation relationship between soft-sphere and quasi-granular model, and proposes to adopt the method. A general connection model between different regions can be used to construct arbitrarily complex interfaces while maintaining the quasi-particle transition layer outside the soft sphere. Simple geometry and fixed particle boundary conditions are also established for the coupling simulation, which improves the practicability of the method. In the fifth chapter, the effect of interface structure on diffusion and reaction process in gas-solid interface reaction is studied by using the coupling simulation method. It is found that the interface structure exists most under given reaction conditions due to the different ways in which diffusion and reaction process interact under different conditions. By establishing a more realistic and detailed model of reactants and interfaces, the coupling method is expected to provide a mechanism analysis and optimization tool, such as the design of catalyst pore structure.
【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】：2016
【分類號】：TQ021
本文編號：2188733
[Abstract]:Nano-micro flow and transfer processes exist widely in chemical engineering, such as the interface of multiphase media, multistage channels in catalyst particles, and micro-chemical systems. With the increasing requirements for precise design and control of chemical processes and equipment, it becomes more and more important to understand the mechanism of these processes. At nano-micro scale, dynamic processes are becoming more and more important. There are still many difficulties in the comprehensive experimental study, but the traditional continuum simulation method gradually fails with the increase of the system characteristic Knudsen number. At this scale, fluids show more discrete properties of molecules, so the application of various discrete particle methods has been widely valued in recent years, but there is a contradiction between the calculation speed and accuracy. The main contents of this paper are as follows: In the introduction part, the soft sphere and the hard sphere are analyzed. Some typical discrete particle simulation methods, such as sphere, quasi-particle and direct simulation Monte Carlo, and their respective advantages and disadvantages, as well as the previous work on coupling different models, are proposed in this paper. That is, the rigid soft sphere model (or its combination) is used to simulate the complex process of dense or close to the interface, while the hard sphere is simplified. The model (or its combination) simulates the gas flow and diffusion processes in thin and far-from-the-wall conditions, and provides the transition and local approximation in the hard-sphere parallel simulation by combining the advantages of both quasi-particle simulation. In Chapter 2, the coupling and parallel methods of event-driven hard-sphere simulation and time-driven quasi-particle simulation are improved. The conversion relationship between hard sphere and pseudo-particulate matter is strictly determined, and its correctness is verified in the simulation of flow and diffusion in pipe. The results show that the coupling can effectively overcome the problems of poor expansibility of hard sphere simulation and low efficiency of pseudo-particulate simulation for rarefied gas, and realize efficient and accurate large-scale parallel simulation. The non-equilibrium diffusion in nano-microporous channels and the diffusion in complex porous media show the feasibility of its practical application in micro-chemical process and catalyst development. In the third chapter, the soft sphere simulation method is deeply studied from two aspects of algorithm improvement and parallel optimization, and the multi-shell neighbor list algorithm about particle search is innovatively put forward.The algorithm effectively improves the search efficiency by simply predicting the possibility of particles crossing each shell.On this basis, the multi-threading and direction of soft sphere simulation are developed. Based on the above work, Chapter 4 finally realizes the coupling of soft-sphere, hard-sphere and quasi-granular simulation. The paper derives the parameter transformation relationship between soft-sphere and quasi-granular model, and proposes to adopt the method. A general connection model between different regions can be used to construct arbitrarily complex interfaces while maintaining the quasi-particle transition layer outside the soft sphere. Simple geometry and fixed particle boundary conditions are also established for the coupling simulation, which improves the practicability of the method. In the fifth chapter, the effect of interface structure on diffusion and reaction process in gas-solid interface reaction is studied by using the coupling simulation method. It is found that the interface structure exists most under given reaction conditions due to the different ways in which diffusion and reaction process interact under different conditions. By establishing a more realistic and detailed model of reactants and interfaces, the coupling method is expected to provide a mechanism analysis and optimization tool, such as the design of catalyst pore structure.
【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】：2016
【分類號】：TQ021
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