共查询到18条相似文献,搜索用时 515 毫秒
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运用计算流体力学(CFD)的方法,采用多相流与粒数衡算方程的耦合求解模型,以10 L体积的内循环带有导流筒和挡板的DTB型结晶器为结构,在考虑晶体成长和成核的条件下,模拟了KCl-H2O体系的连续结晶过程。模拟设定1个连续相和5个不同尺寸晶体的分散相,考察了不同进料流速和进料质量浓度下连续结晶过程的流场分布和固体悬浮等情况,进而从流体动力学特征、过饱和度分布和晶体的粒度分布等特征参数来分析其对结晶过程的影响。模拟结果表明,进料流速和进料质量浓度均对过饱和度分布和晶体粒数密度分布具有明显的影响,而对流场分布情况影响不大。 相似文献
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在考虑晶粒成核、生长、聚并和破碎的情况下,采用分组法求解粒数衡算方程,通过耦合粒数衡算与多相流方程,建立了多尺度的结晶模型,模拟了表面刮削式制冰装置内水的动态结晶过程,获得不同温度、刮削速度、制冰时间等外界条件下晶粒数密度分布、云图等信息,分析了外界宏观条件对水的动态结晶过程的影响。结果表明:由于碰撞引起的晶粒聚并和破碎使得晶粒的尺寸分布更为集中和均匀;在过冷温差(流体局部温度与水的相变温度差值)不大于20℃,刮削速度不大于10 r·s-1范围内,降低壁面温度、增加刮削速度可以加速水的结晶与生长。 相似文献
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精馏塔板上气泡尺寸分布是计算精馏塔板效率以及设计和操作精馏塔的关键参数,但对它的预测受到理论不完善、实验测试手段落后及求解计算困难等方面的限制。本文以Kolmogoroff各向同性湍流理论为基础并结合格率理论,利用计算机图形处理技术对气泡的尺寸分布现象进行观察,分析气泡的聚并和破裂机理。通过已建立的气泡破裂和聚并速率模型,得到精馏塔板上气泡粒数衡算方程。针对气泡粒数衡算方程求解的复杂性,本文采用了Monte Carlo模拟技术来简化气泡粒数衡算方程的求解。求解结果与实验数据相吻合并显示气泡尺寸分布为对数正态分布,这与其他研究者的结论相一致。由所求得的气泡尺寸分布可以进一步计算出气泡的Sauter平均直径以及气液相界面积。 相似文献
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Coupled Calculation of Bubble Size Distribution and Flow Fields in Bubble Columns In this paper the use of computational fluid dynamics (CFD) for the calculation of flow fields in bubble columns is explained. The local bubble size distribution is considered with the aid of a simplified balance equation for the average bubble volume in bubbly flow. Models are developed for the rate of bubble break‐up and coalescence based on physical principals. The flow fields in cylindrical bubble columns without internals are calculated using the Euler‐Euler method. The small and large bubble fraction are considered as pseudo‐continuous phases in addition to the liquid phase. The calculated flow fields are characterised by several large scale vortices. The local volume fractions of gas and liquid are very inhomogeneous and highly time dependent. The calculated volume fractions, velocities and bubble size distributions agree well with experimental results for bubble columns up to 0.3 m in diameter. 相似文献
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A CFD model for the simulation of gas‐liquid bubbly flow is developed. In the model, the multi‐phase flow is simulated by an Eulerian‐Eulerian approach using several phase definitions (from 3 to 10). The bubble size distribution is simulated by a solution of the discretized population balance equation with coalescence and break‐up of bubbles. The number of the discretized population balance equations in the model is larger than the number of the phases used in the flow field simulation. A desired accuracy in the simulation can be achieved by choosing a suitable number of phases as a compromise between accuracy and computational cost. With this model, more detailed flow hydrodynamics and bubble size distribution can be obtained. The model was tested with different operating conditions and for different numbers of dispersed phases in a bubble column, and was verified with a bubble size distribution obtained experimentally. 相似文献
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Guangchun Song Yuxing Li Wuchang Wang Kai Jiang Zhengzhuo Shi Shupeng Yao 《中国化学工程学报》2019,27(1):32-43
Dynamic modeling and numerical simulation of hydrate slurry flow behavior are of great importance to offshore hydrate management.For this purpose, a dynamic model of hydrate agglomeration was proposed in this paper.Based on population balance equation, the frame of the dynamic model was established first, which took both hydrate agglomeration and hydrate breakage into consideration.Then, the calculating methods of four key parameters involved in the dynamic model were given according to hydrate agglomeration dynamics.The four key parameters are collision frequency, agglomeration efficiency, breakage frequency and the size distribution of sub particles resulting from particle breakage.After the whole dynamic model was built, it was combined with several traditional solid–liquid flow models and then together solved by the CFD software FLUENT 14.5.Finally, using this method, the influences of flow rate and hydrate volume fraction on hydrate particle size distribution, hydrate volume concentration distribution and pipeline pressure drop were simulated and analyzed. 相似文献
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A. Gäbler 《Chemical engineering science》2006,61(9):3018-3024
A novel parameter study with experimental and numerical investigations of transient drop size distributions was carried out in order to study published model approaches for dispersed systems on the basis of the population balance equation. In terms of breakage and coalescence behaviour the dependency of the drop size distributions on power input, phase fraction, and especially pH was studied with the system toluene-water. With higher pH, coalescence is hindered considerably. As a consequence, the transient evolution of drop size distributions after starting the stirrer is changing and the time for reaching the stationary distribution increases. For the simulation applying the breakage and coalescence models a very efficient solver for the population balance equation (PBE), the program PARSIVAL® is used. The simulation results of transient drop size distributions are in good agreement with the experimental data for various power inputs. The influence of the dispersed phase fraction is not characterized correctly.A proportionality between the Sauter mean diameter and the Weber number d32∼We-0.5 was measured for pH 13 and different phase fractions. The commonly reported exponent -0.6 for systems with low coalescence seems to be not applicable with higher pH and increased dispersed phase fraction. 相似文献
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两相及多相体系的离散相行为与群体平衡模型 总被引:1,自引:1,他引:0
气体、固体和液体共存的两相及多相系统广泛存在于自然界和过程工业领域。两相及多相系统的研究方法有直接模拟法、离散颗粒模拟和双流体模型等.直接模拟法和离散颗粒模拟需要研究离散相的特征及物理过程,而提高双流体模型的精度,也必须注意离散相的分布特征以及微观行为,以确定相间相互作用.群体平衡模型作为一种联系离散相微观行为与宏观表征的方法,已经成为研究离散系统的有效工具。群体平衡模型可以描述不同操作过程离散相实体的微观行为.结合不同的多相系统的特点,对群体平衡模型的物理意义、方程形式和应用进行分析,从计算资源消耗、实现难易程度及其计算精度三方面对群体平街模型求解方法进行了比较,提出了群体平衡模型应用中存在的问题和发展方向. 相似文献
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液滴平均尺寸和液滴尺寸分布是描述不溶液-液分散程度的2个重要参数,决定着两相接触面积的大小,进而决定着相间的传质、传热和化学反应速率。利用CFD方法详细研究了水-油两相在搅拌槽内的分散过程,发现叶轮转速、分散相体积分数和连续相黏度对分散效果有显著影响。当两相组成一定时,增大叶轮转速和连续相黏度均有利于两相的分散。在一定范围内,液滴平均直径与叶轮转速、分散相体积分数均为对数线性关系,相关系数高达0.999。基于个数的液滴尺寸分布在不同转速和连续相黏度条件下出现了双峰分布,而基于体积的液滴尺寸分布则始终为单峰分布。 相似文献
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提升管内气固流动行为的数值模拟 总被引:3,自引:0,他引:3
应用计算流体力学软件Fluent,对空气为连续相、固相为催化裂化反应催化剂的循环流化床提升管内的气固流动行为进行模拟。采用用户自定义函数引入颗粒与壁面的恢复系数和颗粒的镜面反射系数,对颗粒在边壁处的部分滑移运动进行描述。采用不同的计算动力学模型及参数,数值模拟了径向颗粒浓度、轴向床层压降的空间分布,以及用以描述颗粒脉动动能的颗粒温度与固含率的关系,并与文献报道的实验和数值模拟结果进行对比分析。结果表明,选取的颗粒动力学理论模型及参数、颗粒部分滑移边界条件及气固曳力模型,可计算得到合理的颗粒轴向及径向分布,验证了提升管中存在典型的径向环核流动结构和轴向压降分布。进一步分析表明固含率显著影响颗粒温度,当固含率为0.05~0.1,颗粒温度存在转折区。 相似文献