非球形颗粒典型流化床气固两相流数值模拟及实验研究
发布时间：2018-07-31 19:40
【摘要】：气固两相颗粒系统广泛存在于自然界和工业过程中。而在当前针对流化床内气固两相流动的研究中,通常基于球形颗粒的假设。尽管这样能够降低研究难度,但是不可避免的引入了误差,尤其是造成了颗粒运动及脉动的各向异性特性缺失,导致了气固两相颗粒系统内颗粒动力学特性的不同。在近期逐渐开展起来的非球形颗粒系统研究也主要应用离散单元模型(Discrete Element Method,DEM)中的软球模型,使用硬球模型的研究还未见报道,相关机理与模型研究仍需进一步的探索。本文基于非球形颗粒间动量和能量守恒原理,应用DEM硬球模型研究了非球形颗粒稠密气固两相流动中的颗粒行为。以组合颗粒模型为基础,采用四元数理论描述非球形颗粒的运动。对于颗粒碰撞搜寻算法,提出了几何代数两步搜寻方法,大大减少了非球形颗粒搜寻算法的计算需求,并保证了计算精度。基于Routh的图解法,结合Poisson恢复系数假设和Coulumb定律,建立了适用于非球形颗粒的三维碰撞模型。基于PIV技术搭建了喷动床实验台,开展了非球形颗粒流态化行为的实验研究,并应用本文建立的非球形颗粒DEM硬球模型进行了相同操作条件下喷动床内颗粒行为的数值模拟研究。与球形颗粒相比,非球形颗粒喷动床内颗粒的运动更为剧烈,颗粒的扬析现象更为明显,床内气泡的边界较为模糊,并且气泡内包含较多分散颗粒。对比数值模拟与实验测量结果,可以看出应用非球形颗粒硬球模型得到的结果与实验结果吻合较好,速度分布趋势基本相同。应用建立的非球形颗粒离散颗粒硬球模型,对鼓泡流化床内气固两相流体动力学特性进行了数值模拟研究。鼓泡流化床内首先进行了球形颗粒动力特性的数值模拟研究,并得到了非常规重力加速度条件下颗粒的鼓泡行为。随后,对比了非球形颗粒和球形颗粒的速度、颗粒分离情况、气泡行为和颗粒的脉动运动等,获得了不同弹性恢复系数和重力加速度条件下非球形颗粒的动力学特性。对单组份鼓泡流化床,非球形颗粒系统的气固分布周期性规律较为复杂,并且在系统内气泡的边界并不清晰,内部存在大量分散的颗粒,气泡的脉动运动趋势不明显,而颗粒的微观脉动运动与气泡的行为有着密切的联系。对于双组份鼓泡流化床,非球形颗粒双组份鼓泡流化床中颗粒的混合较为均匀,其中气泡的脉动运动要强于球形颗粒系统。应用建立的非球形颗粒离散颗粒硬球模型,对喷动流化床内气固两相流体动力学特性进行了数值模拟研究。应用区域相关的颗粒行为分析方法,获得了非球形颗粒与球形颗粒喷动流化床流态化特性在空间上的关联。研究表明球形颗粒喷动流化床中的分区方式是以床内中部为中心,不同的流化区域呈环形分布。而在非球形颗粒系统中,其分区呈现分层的形式。不同的分区特性表明球形颗粒与非球形颗粒的流态化行为存在较大的差异。应用建立的非球形颗粒离散颗粒硬球模型,对喷动流化床内气固两相流体动力学特性进行了数值模拟研究。开展了非球形颗粒和球形颗粒系统内颗粒聚团微观脉动特性的研究,提出了广义的聚团颗粒温度的概念,用于考察颗粒系统中聚团的脉动运动。对球形颗粒系统,不同曳力模型下的聚团颗粒温度分布差别较大。大颗粒的分布更集中,小颗粒分布更分散。对非球形颗粒系统,提升管中的颗粒位置分布较为均匀,聚团的微观脉动运动也相对较弱。与球形颗粒系统类似,小颗粒的广义聚团颗粒温度比大颗粒的数值更大,说明了小颗粒及其颗粒聚团的脉动运动更剧烈。
[Abstract]:Gas-solid particle systems are widely used in natural and industrial processes. In the current study of gas-solid two-phase flow in a fluidized bed, the assumption of spherical particles is usually based on the assumption that it can reduce the difficulty of the study, but the error is inevitably introduced, especially the anisotropy of the particle motion and the pulsation. The loss is different in the particle dynamics in the gas-solid particle system. The research on the soft sphere model in the discrete element model (Discrete Element Method, DEM) is also mainly used in the recent development of the non spherical particle system. The research on the hard ball model has not been reported, and the related mechanism and model research still need to be further studied. In this paper, based on the principle of momentum and energy conservation among non spherical particles, the particle behavior in dense gas-solid two-phase flow of non spherical particles is studied by using the DEM hard ball model. Based on the combined particle model, the motion of non spherical particles is described by the four element number theory. Two steps of geometric algebra are proposed for the search algorithm of particle collision. In search method, the calculation requirement of non spherical particle search algorithm is greatly reduced and the calculation accuracy is guaranteed. Based on the graphical method of Routh, a three-dimensional collision model suitable for non spherical particles is established by combining the Poisson recovery coefficient hypothesis and the Coulumb law. A spouted bed experiment platform is built based on PIV technology, and the non spherical particle fluidized bed is carried out. For the experimental study, the numerical simulation of particle behavior in a spouted bed under the same operating conditions was carried out by using the non spherical particle DEM hard ball model established in this paper. Compared with the spherical particle, the motion of the particles in the non spherical particle spouted bed is more intense, the particle's uplift phenomenon is more obvious, the boundary of the bubble in the bed is more blurred. There are more dispersed particles in the bubble. Comparing the numerical simulation and the experimental results, it can be seen that the results obtained by the non spherical particle hard ball model are in good agreement with the experimental results, and the velocity distribution trend is basically the same. The application of the established non spherical particle discrete particle hard ball model to the gas-solid two-phase fluid dynamics in the bubbling fluidized bed The numerical simulation of the characteristics was carried out. The numerical simulation of the dynamic characteristics of the spherical particles was first carried out in a bubbling fluidized bed, and the bubbling behavior of the particles under the unconventional gravity acceleration was obtained. Then, the velocity of the non spherical and spherical particles, the particle separation, the bubble behavior and the pulsating motion of the particles were obtained. The dynamic characteristics of non spherical particles under the conditions of different elastic recovery coefficient and gravity acceleration are obtained. The periodic regularity of gas solid distribution in a single component bubbling fluidized bed is complicated, and the boundary of bubbles is not clear in the system, and there are a large number of dispersed particles in the interior of the system, and the fluctuating movement trend of the bubbles is not obvious. The microcosmic pulsation movement of the particles is closely related to the behavior of the bubbles. For the double component bubbling fluidized bed, the particle mixing in the bubbling fluidized bed with non spherical particles is more uniform, and the pulsation motion of the bubble is stronger than the spherical particle system. The application of the established non spherical particle discrete particle hard ball model to the spouted flow The aerodynamic characteristics of the gas-solid two-phase fluid in the bed are numerically simulated. The spatial correlation of the fluidization characteristics of the non spherical particles and the spherical particles in the spout fluidized bed is obtained by the method of region related particle behavior analysis. The study shows that the partition mode of the spherical particle spouted fluidized bed is centered in the middle of the bed. In the non spherical particle system, the zone presents a stratified form in the non spherical particle system. The different characteristics of the zoning show that there is a great difference in the fluidization behavior between the spherical particles and the non spherical particles. The application of the established non spherical particle discrete particle hard ball model is used to improve the gas-solid two-phase fluid dynamics in the spouted fluidized bed. The study on the microcosmic pulsation characteristics of the particles in the non spherical and spherical particles system has been carried out. The concept of the generalized cluster particle temperature is proposed to investigate the pulsating motion of the cluster in the particle system. The temperature distribution of the particles in the spherical particle system is different from that of the different drag models. The distribution of particles is more concentrated and the distribution of small particles is more dispersed. In the non spherical particle system, the distribution of particles in the riser is more uniform and the micropulsation motion of the cluster is relatively weak. Similar to the spherical particle system, the temperature of the small particles in the generalized agglomeration particles is larger than that of the large particles, indicating the pulsation of the small particles and their particles. Exercise is more intense.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O359
本文编号：2156626
[Abstract]:Gas-solid particle systems are widely used in natural and industrial processes. In the current study of gas-solid two-phase flow in a fluidized bed, the assumption of spherical particles is usually based on the assumption that it can reduce the difficulty of the study, but the error is inevitably introduced, especially the anisotropy of the particle motion and the pulsation. The loss is different in the particle dynamics in the gas-solid particle system. The research on the soft sphere model in the discrete element model (Discrete Element Method, DEM) is also mainly used in the recent development of the non spherical particle system. The research on the hard ball model has not been reported, and the related mechanism and model research still need to be further studied. In this paper, based on the principle of momentum and energy conservation among non spherical particles, the particle behavior in dense gas-solid two-phase flow of non spherical particles is studied by using the DEM hard ball model. Based on the combined particle model, the motion of non spherical particles is described by the four element number theory. Two steps of geometric algebra are proposed for the search algorithm of particle collision. In search method, the calculation requirement of non spherical particle search algorithm is greatly reduced and the calculation accuracy is guaranteed. Based on the graphical method of Routh, a three-dimensional collision model suitable for non spherical particles is established by combining the Poisson recovery coefficient hypothesis and the Coulumb law. A spouted bed experiment platform is built based on PIV technology, and the non spherical particle fluidized bed is carried out. For the experimental study, the numerical simulation of particle behavior in a spouted bed under the same operating conditions was carried out by using the non spherical particle DEM hard ball model established in this paper. Compared with the spherical particle, the motion of the particles in the non spherical particle spouted bed is more intense, the particle's uplift phenomenon is more obvious, the boundary of the bubble in the bed is more blurred. There are more dispersed particles in the bubble. Comparing the numerical simulation and the experimental results, it can be seen that the results obtained by the non spherical particle hard ball model are in good agreement with the experimental results, and the velocity distribution trend is basically the same. The application of the established non spherical particle discrete particle hard ball model to the gas-solid two-phase fluid dynamics in the bubbling fluidized bed The numerical simulation of the characteristics was carried out. The numerical simulation of the dynamic characteristics of the spherical particles was first carried out in a bubbling fluidized bed, and the bubbling behavior of the particles under the unconventional gravity acceleration was obtained. Then, the velocity of the non spherical and spherical particles, the particle separation, the bubble behavior and the pulsating motion of the particles were obtained. The dynamic characteristics of non spherical particles under the conditions of different elastic recovery coefficient and gravity acceleration are obtained. The periodic regularity of gas solid distribution in a single component bubbling fluidized bed is complicated, and the boundary of bubbles is not clear in the system, and there are a large number of dispersed particles in the interior of the system, and the fluctuating movement trend of the bubbles is not obvious. The microcosmic pulsation movement of the particles is closely related to the behavior of the bubbles. For the double component bubbling fluidized bed, the particle mixing in the bubbling fluidized bed with non spherical particles is more uniform, and the pulsation motion of the bubble is stronger than the spherical particle system. The application of the established non spherical particle discrete particle hard ball model to the spouted flow The aerodynamic characteristics of the gas-solid two-phase fluid in the bed are numerically simulated. The spatial correlation of the fluidization characteristics of the non spherical particles and the spherical particles in the spout fluidized bed is obtained by the method of region related particle behavior analysis. The study shows that the partition mode of the spherical particle spouted fluidized bed is centered in the middle of the bed. In the non spherical particle system, the zone presents a stratified form in the non spherical particle system. The different characteristics of the zoning show that there is a great difference in the fluidization behavior between the spherical particles and the non spherical particles. The application of the established non spherical particle discrete particle hard ball model is used to improve the gas-solid two-phase fluid dynamics in the spouted fluidized bed. The study on the microcosmic pulsation characteristics of the particles in the non spherical and spherical particles system has been carried out. The concept of the generalized cluster particle temperature is proposed to investigate the pulsating motion of the cluster in the particle system. The temperature distribution of the particles in the spherical particle system is different from that of the different drag models. The distribution of particles is more concentrated and the distribution of small particles is more dispersed. In the non spherical particle system, the distribution of particles in the riser is more uniform and the micropulsation motion of the cluster is relatively weak. Similar to the spherical particle system, the temperature of the small particles in the generalized agglomeration particles is larger than that of the large particles, indicating the pulsation of the small particles and their particles. Exercise is more intense.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O359
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