计算流体力学在顺流喷雾干燥器模拟中的误差源研究

The paper is focused on identifying error sources in computational fluid dynamics(CFD) predictions of a spray drying process. Seven groups of drying and atomisation parameters were selected for analysis and 13 simulation trials were performed. The theoretical results were compared with experimental data and sensitivity of the simulation results to the analysed factors was determined. The following parameters affecting the accuracy of CFD spray modelling were found: gas turbulence model, particle dispersion, atomising air, initial parameters of atomisation and heat losses to the environment. A major difference in the errors committed during modelling of spray drying process for fine and coarse sprays was observed.     

Droplet-Droplet Interactions in Spray Drying by Using 2D Computational Fluid Dynamics

A 2D axisymmetric model of the spray drying process is presented. The two-phase flow theoretical model is based on a combined Eulerian-Lagrangian approach and takes binary interactions (coalescence or bouncing) between spray droplets into consideration. Validation of the model (incorporated in FLUENT 6.3.26) demonstrated good agreement and consistency with the literature data. The results of transient simulations showed that droplet-droplet interactions displace the region of heat and mass transfer from the central core toward the periphery of the drying chamber. It was also found that insulation of the spray dryer can substantially affect temperature and humidity patterns, whereas its influence on the velocity flow field is less marked.     

CFD 在食品干燥过程及其干燥设备设计中的应用

CFD是通过计算机数值计算和图像显示以定量描述流场的数值解,从而对物理问题进行分析研究。CFD兼有理论性和实践性的双重特点,其主要用途是对流态进行数值仿真模拟计算,能够对流态的温度场、速度场、浓度场等进行有效的指导和预测。本文综述了CFD数值模拟在食品干燥过程中以及干燥设备设计中的应用和发展前景。     

计算流体力学在二沉池改造中的应用

利用计算流体力学对污水处理厂二沉池内流场进行了数值模拟,得到二沉池内流场速率分布规律,进而确定流态临界位置水流速率,并将其作为标准速率。基于此,在二沉池内对挡板结构进行改造。改造后二沉池的模拟计算结果表明,二沉池在保证出水水质的情况下很好地满足了增大处理量的要求。     

规整填料塔内两相流动的三维计算流体力学建模(英文)

Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.     

Three-dimensional Computational Fluid Dynamics Modeling of Two-phase Flow in a Structured Packing Column

Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power-ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model...     

Computational Fluid Dynamics for Multistage Adsorption Dryer Design

Two-dimensional computational fluid dynamics calculations for multistage zeolite drying are performed for two dryer configurations (1) a continuous moving bed zeolite dryer and (2) a discrete bed zeolite dryer. The calculations concern drying of tarragon (Artemisia dracunculus L.) as an herbal product. The results reveal the profiles of water, vapor, and temperature in dryer, adsorber, and regenerator in the flow directions. The thermal efficiency ranges between 80 and 90% and is close to overall model calculations. The performance of continuous moving bed zeolite dryer is the best. Residence time of air, product, and zeolite are in accordance to other drying systems.     

Computational Fluid Dynamics for Multistage Adsorption Dryer Design

Two-dimensional computational fluid dynamics calculations for multistage zeolite drying are performed for two dryer configurations (1) a continuous moving bed zeolite dryer and (2) a discrete bed zeolite dryer. The calculations concern drying of tarragon (Artemisia dracunculus L.) as an herbal product. The results reveal the profiles of water, vapor, and temperature in dryer, adsorber, and regenerator in the flow directions. The thermal efficiency ranges between 80 and 90% and is close to overall model calculations. The performance of continuous moving bed zeolite dryer is the best. Residence time of air, product, and zeolite are in accordance to other drying systems.     

A Parametric Study of the Gas Flow Patterns and Drying Performance of Co-current Spray Dryer: Results of a Computational Fluid Dynamics Study

Abstract

A computational fluid dynamic study was carried out to investigate airflow pattern, temperature, and humidity profile at different levels in the drying chamber. Good agreement was obtained with published experimental data. The effects of operating pressure, heat loss from the chamber wall and inlet air conditions on the gas flow pattern, droplet trajectories, and overall dryer performance also were investigated. Results are presented and discussed in terms of the gas velocity, temperature, and humidity profiles within the chambers. The volumetric evaporation values, heat transfer intensity, and thermal energy consumption per unit evaporation rate were computed and compared for drying of a 42.5% solids solution in a spray chamber 2.215 m in diameter with a cylindrical top section 2.005 m high and a bottom cone 1.725 m high. Wall regions subject to formation of undesirable deposits are also identified.     

Computational Fluid Dynamics versus Experiment: An Investigation on Liquid Weeping of Nye Trays

The weeping phenomenon was investigated using some experimental tests and a numerical model. The tests were performed within a 1.22‐m‐diameter pilot‐scale column including two chimney trays and two Nye test trays with an air‐water system. The rates of weeping were measured in the Nye trays with two heights of the weir and a hole area of 5 %. Moreover, the weeping rates in the outlet and inlet halves of the Nye tray and the total weeping rate were calculated. In the next step, an Eulerian‐Eulerian computational fluid dynamics (CFD) technique was used. The results show good agreement between the attained CFD findings and the experimental data.     

A Parametric Study of the Gas Flow Patterns and Drying Performance of Co-current Spray Dryer: Results of a Computational Fluid Dynamics Study

A computational fluid dynamic study was carried out to investigate airflow pattern, temperature, and humidity profile at different levels in the drying chamber. Good agreement was obtained with published experimental data. The effects of operating pressure, heat loss from the chamber wall and inlet air conditions on the gas flow pattern, droplet trajectories, and overall dryer performance also were investigated. Results are presented and discussed in terms of the gas velocity, temperature, and humidity profiles within the chambers. The volumetric evaporation values, heat transfer intensity, and thermal energy consumption per unit evaporation rate were computed and compared for drying of a 42.5% solids solution in a spray chamber 2.215 m in diameter with a cylindrical top section 2.005 m high and a bottom cone 1.725 m high. Wall regions subject to formation of undesirable deposits are also identified.     

计算流体力学在填充床反应器中的应用进展

在使用计算流体力学(CFD)方法模拟填充床反应器时,为了描述填充床中的气液流动情况,目前主要运用基于体积平均法的双流体数学模型,辅以空隙率分布,填料润湿效率以及轴向扩散等经验关联式来计算填充床中的压降、持液量、停留时间分布等重要参数。近年来填充床反应器CFD数学模型韵几个研究重点是动量交换系数、毛细管压力以及床层空隙率的非均匀分布性。简要介绍了涓流床、固定床、填料塔等填充床反应器及其内部构件研究中CFD软件模拟的应用进展情况和发展趋势。     

The Drying of Sludge in a Cyclone Dryer Using Computational Fluid Dynamics

A control volume-based technique implemented in FLUENT (ANSYS Inc., Canonsburg, PA) computational fluid dynamics (CFD) package was applied along with the kinetic theory of granular flow (KTGF) to simulate the flow pattern and heat and mass transfer processes for sludge material in a large-scale cyclone dryer. The drying characteristics of sludge at the dryer inlet were obtained from a previous study on the drying of sludge in a large-scale pneumatic dryer. User-defined subroutines were added to extend FLUENT's capability to account for mixture properties and to simulate the constant and falling rate drying periods. The convective heat and mass transfer coefficients were modeled using published correlations for Nusselt and Sherwood numbers. Sensitivity analysis was conducted to determine the effect of gas-phase velocity and temperature on the final product outcome. Numerical predictions for the multiphase flow hydrodynamics showed a highly diluted region in the dryer core and a higher concentration of particles close to the wall region, an indication of nonuniform distribution of particles at a cross-sectional area. The numerical predictions for the hydrodynamic profiles qualitatively depicted the flow behavior natural to these designs. The work demonstrated the successful application of CFD in the design stage of a combined pneumatic-cyclone dryer model.     

旋流板内两相流场的CFD模拟与分析

The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The simulation is based on the two-equation RNG κ-ε turbulence model, Eulerian multiphase model, mad a real-shape 3D model with a huge number of meshes. The simulation results include detailed information about velocity, pressure, volume fraction and so on. Some features of the flow field are obtained: liquid is atomized in a thin annular zone; a high velocity air zone prevents water drops at the bottom from flying towards the wall;the pressure varies sharply at the end of blades and so on. The results will be helpful for structure optimization and engineering design.     

Use of Computational Fluid Dynamics to Evaluate Alternative Spray Dryer Chamber Configurations

A computational fluid dynamic simulation study was carried out to compare the gas flow and temperature patterns as well as particle trajectories for a pressure nozzle atomized liquid slurry spray dried in four different chamber geometries. The gas and liquid conditions are held the same for all four chamber geometries. The gas flow is co-current and enters and exits centrally thus maintaining a two-dimensional axi-symmetric flow pattern. It is found that as a result of variations in the gas flow and thermal patterns in the four configurations examined (viz cylinder-on-cone, conical, hour-glass shaped, and lantern-shaped axi-symmetric) the droplet trajectories, residence times, and drying times vary. It was noted that the effective chamber volume occupied by drying particles depends on the chamber design.     

Use of Computational Fluid Dynamics to Evaluate Alternative Spray Dryer Chamber Configurations

Abstract

A computational fluid dynamic simulation study was carried out to compare the gas flow and temperature patterns as well as particle trajectories for a pressure nozzle atomized liquid slurry spray dried in four different chamber geometries. The gas and liquid conditions are held the same for all four chamber geometries. The gas flow is co-current and enters and exits centrally thus maintaining a two-dimensional axi-symmetric flow pattern. It is found that as a result of variations in the gas flow and thermal patterns in the four configurations examined (viz cylinder-on-cone, conical, hour-glass shaped, and lantern-shaped axi-symmetric) the droplet trajectories, residence times, and drying times vary. It was noted that the effective chamber volume occupied by drying particles depends on the chamber design.     

圆环挡板振荡流反应器的计算流体动力学研究

采用并行计算技术和2237267个格栅的非结构化网格模型.成功地进行了具有完整结构的十腔室圆环挡板振荡流反应器的数值模拟研究,获得了进料腔室、标准腔室和出料腔室的流场结构和特征.对标准腔室的计算流场和实验流场图像的对比显示两者吻合良好.模拟结果表明,标准腔室中的主流区和二次流区的径向位置在每个振荡周期中交换一次.而除了底部腔室以外的其余腔室中的二次流区漩涡在整个振荡周期中始终存在.进一步的研究将针对二次流区漩涡的动态行为进行.     

喷雾干燥的研究进展

介绍了国内外喷雾干燥领域的最新研究进展,阐述了喷雾冷冻干燥、超临界喷雾干燥等方面的研究结果,探讨了关于喷雾干燥过程数学模拟的研究方法和结论,总结、归纳并提出了目前国内外较新的关于喷雾干燥的研究课题和方向。     

Measurements of Particle Residence Time Distributions in A Co-Current Spray Dryer

ABSTRACT

Measurements of particle residence time distributions by means of tracer analysis were done in a co-current pilot plant spray dryer operated with a pressure–nozzle. A system is described for injecting tracer into the feedstream just before the nozzle. Tracer concentrations were measured in two product streams: the tower product stream (mean particle size 134 microns) and the cyclone product stream (mean particle size 67 microns). The measurements show a very wide range of residence times: some particles have residence times shorter than 3 seconds, others have residence times longer than 10 minutes. The median of the distribution is 58·5 _s for the tower product stream and 42.2 _s for the cyclone product stream.