Population balance modelling of protein precipitates exhibiting turbulent flow through a circular pipe

The breakage of liquid-liquid, solid-liquid and solid-gas dispersions occurs in many industrial processes during the transport of particulate materials. In this work, breakage of whey protein precipitates passing through a capillary pipe is examined and an experimentally derived breakage frequency is applied to construct a suitable population balance model to characterize the breakage process. It has been shown that the breakage frequency of precipitate particles is highly dependent on their shear history and on the turbulent energy dissipation rate in the pipe. The population balance equation (PBE) uses a volume density based discrete method which is adapted from mass density based discretization. In addition to comparing the model with experimental data, predicted results at different velocities are presented. It was found that the population balance breakage model provides satisfactory results in terms of predicting particle size distributions for such processes.     

Liquid flow and phase holdup—measurement and CFD modeling for two-and three-phase bubble columns

Bubble columns are an important class of contacting devices in chemical industry and biotechnology. Their simple setup makes them ideal reactors for two- and three-phase operations such as fermentations or heterogeneous catalysis. Still, design and operation of these reactors is subject to widely empirical scale-up strategies. With recent advances in the development of measurement techniques, a more detailed approach to the development of optimized reactors for specific operations should become possible. This report is based on detailed measurements of local dispersed phase holdups in a pilot plant-sized bubble column operated at high superficial gas velocities and solid holdups. It deals with the influence of superficial gas velocity, solid loading and sparger geometry on measured and computed liquid flow velocities and holdup distributions. Liquid velocity measurements have been performed using the electrodiffusion method, modeling calculations have been carried out using the computational fluid dynamics (CFD) code CFX-4.3. Measurement results presented here give an insight into the development of liquid circulation and fluctuating velocity distribution depending on superficial gas velocity, solid loading and sparger geometry. CFD results implementing a multi-fluid model with k-ε turbulence and special momentum exchange terms for direct gas-solid interactions show that, even on standard PC workstations, this kind of computations can deliver qualitatively reasonable agreement with measurements.     

Simulation and experiment of flow field in axial-flow hydrocyclone

Axial-flow hydrocyclone is a new type of hydrocyclone which is proposed on the basis of tangential hydrocyclone. Its key part is rotating and accelerating component - the guided vane. The structural particularity made it necessary to pay attention to the internal flow field of axial-flow hydrocyclone. In view of the progress of CFD technique and mature of calculation condition, numerical simulations were carried on single-phase flow in axial-flow hydrocyclone by using Fluent software and Reynolds Stress Model. The initial conditions were that fluid medium was water and the overflow rate was 15%. The pressure and velocities fields were analyzed in the whole hydrocyclone and the specific effects of guided vane were studied. At the same time, through the verification of LDV experiment, the simulated values of water phase matched well with the experimental values.     

Numerical modelling of the carrier gas phase in a laboratory-scale coal classifier model

The pneumatic transport of fine ideally combustible coal dust to the burner furnace is an important process in coal fired power plants. The strongly swirling air phase responsible for the particle separation and transport in a coal pulverising mill was characterised experimentally and numerically. Measurements of the swirl velocity component were taken in a scaled laboratory model of the device and compared to CFD model. In particular, an evaluation of the turbulence models used to describe the flow was performed. The modified isotropic k-epsilon turbulence models (RNG k-ε and Realizable k-ε) were compared to the anisotropic Reynolds stress model (RSM) and their ability to predict the bulk flow structure present in the classifier was assessed. The experiments showed that the swirling flow structure, responsible for coarse-fine particle classification, has several flow regimes which are governed by the areas it is bounded by. The numerical model predictions generally corroborate the results. However, a distinction in performance between the three models can be made based on accuracy, solution generation time and numerical stability. The RSM model predicted both the trends and magnitude the most accurately when compared to the isotropic models. However, the Realizable k-epsilon model, with its relatively low solution generation time, shows potential when using CFD as a classifier design optimization tool. The investigation has given some insight on single phase classifier flow and suggests a design improvement based on the results.     

不同湍流模型对铅-铋凝固模拟的影响研究

为了研究不同湍流模型及湍流普朗特数（Pr_t）模型对模拟铅-铋凝固行为的影响,利用FLUENT对铅-铋管内流动凝固行为进行模拟研究。研究结果表明,尽管剪切应力传输（k-ω SST）模型、k-ε模型与雷诺应力（RSM）模型在模拟铅-铋传热时的差异可以忽略,但在相变过程中对温度场与压力场的模拟存在显著差异,应慎重选取湍流模型。另外对不同Pr_t模型对铅-铋的凝固行为模拟的研究表明,不同Pr_t模型对铅-铋的凝固行为模拟无明显差异。     

折流板液滴分离的OpenFOAM模拟及验证

为预测折流板中的气液两相流行为,使用OpenFOAM基于Euler-Lagrangian方法以液滴为离散相、气流为连续相模拟了折流板中离散相与连续相双向耦合的流动。其中离散相受曳力作用,连续相分别使用了标准k-ε模型与k-ω SST模型进行模拟。本文介绍了网格的划分,对于OpenFOAM生成的Lagrangian粒子坐标的后处理以及基于OpenFOAM编写的折流板汽水分离效率程序。计算得到不同湍流模型在不同网格下的连续相流场、连续相速度场以及汽水分离效率与实验数据的对比。结果表明,无论是连续相还是离散相,湍流模型相较于网格对于结果的影响更大,k-ω SST模型计算结果更加准确,模型对于大尺寸直径的液滴分离效率预测准确,但是对于小直径液滴的分离效率预测不够准确。