A CFD model of autothermal reforming

A numerical model based on computational fluid dynamics (CFD) was developed and validated to simulate the performance of a catalytic monolith reformer for the production of hydrogen that could be used in fuel cell systems. The whole reactor was modeled as porous media for the process of autothermal reforming with n-hexadecane feed. CFD results provided an adequate match to experimental data from literature with respect to temperature and the mole fractions of H₂, CO₂ and CO products. The percentage difference between each experimental measurement of the mole fraction of hydrogen and the corresponding CFD prediction was less than 16.8%. It was found that the thermal conductivity of the solid catalyst substrate affected the temperature profile in the reactor, but its effect on product hydrogen concentration was negligible. The calculated reforming efficiency based on hydrogen decreased by 11.8% as power input was increased from 1.7 to 8.4 kW.     

Spray drying with a two-fluid nozzle to produce fine particles: Atomization,scale-up,and modeling

This article presents experimental and modeling work to complete previously reported work on spray drying. Back-calculated droplet sizes have been verified by measurements with a laser imaging rig. Flow patterns in a cylindrical spray chamber have been simulated by computational fluid dynamics and demonstrated that droplet residence times are much shorter than expected. A droplet tracking population balance model has been implemented in gSOLIDS and shows how drying times vary with droplet diameter. Particle collection by cyclone and bag filter have also been compared experimentally.     

Particulate flow modelling in a spiral separator by using the Eulerian multi-fluid VOF approach

The Euler-Euler model is less effective in capturing the free surface of flow film in the spiral separator,and thus a Eulerian multi-fluid volume of fluid(VOF) model was first proposed to describe the particulate flow in spiral separators. In order to improve the applicability of the model in the high solid concentration system, the Bagnold effect was incorporated into the modelling framework. The capability of the proposed model in terms of predicting the flow film shape in a LD9 spiral separat...     

缸盖水腔CFD分析及连接钻孔优化

以某柴油机缸盖水腔变动情况为研究对象,对调整前后的缸盖水腔进行CFD仿真。针对缸盖下层水腔、排气道水腔的流速分布云图,结合上水孔及连接钻孔的流量分布,分析流动过程及调整后冷却能力减弱的详细原因。在此基础上,通过调整连接钻孔的直径及位置,提出满足冷却能力要求的优化方案,并对优化方案进行仿真验证。     

涡轮桨搅拌槽内流动特性的大涡模拟

利用大涡模拟方法研究了涡轮桨搅拌槽内的流动特性,采用了三种亚格子模式:标准Smagorinsky-Lilly模式(SLM)、Smagorinsky-Lilly动力模式(DSLM)和亚格子动能动力模式(DKEM),并将模拟结果与标准k-ε模型及文献实验数据进行了详细的比较.结果表明:大涡模拟方法可获得搅拌槽内的瞬态流场;对桨叶区时均速度及湍流动能的预测与实验数据相吻合,比标准k-ε模型计算结果有明显改进,三种亚格子模型中DSLM和DKEM模拟结果更好.同时分析了大涡模拟中桨叶端部附近湍流动能估计偏差的原因,发现主要是由于对轴向湍流均方根速度的预测偏差造成的.大涡模拟方法为搅拌槽内非稳态、周期性的湍流流动和湍流特性的研究提供了强有力的工具.     

柴油机喷雾混合的场效应分析方法研究

柴油机燃烧系统的设计及匹配一直是柴油机研究的重点.提出了一种新的柴油机燃烧系统场效应分析方法,针对喷雾混合过程进行微观及宏观仿真分析研究.场效应分析方法从燃油浓度场和速度场对混合过程的影响规律入手,将这两个场量对传质的作用通过场效应角进行量化,从而对燃烧系统的优劣进行定量的评价,指导燃烧系统的设计或优化匹配.以喷雾锥角的匹配为例应用场效应分析方法进行了仿真研究,并在单缸机上进行了试验验证,证明了场效应分析方法的有效性和实用性.     

CFD simulation of large-scale bubble plumes: Comparisons against experiments

Computational fluid dynamics (CFD) simulations have been carried out to simulate a turbulent, bubble plume in a liquid pool. A two-fluid enhanced k-? model has been used, with the extra source terms introduced to account for the interaction between the bubbles and the liquid and transient calculations have been performed to study the plume growth, the acceleration of the liquid due to viscous drag, and the approach to steady-state conditions. In order to obtain correct spreading of the plume observed experimentally, it was observed that interfacial forces like lift and turbulent dispersion plays important role. The sensitivity analysis for drag coefficient and two different turbulent dispersion forces is presented. The development of the flow variables has been compared with the experimental data. From the CFD predictions obtained in the present work, it can be concluded that a two-dimensional (2D) axisymmetric assumption in this case is justified, with 2D model predictions in good agreement with the experimental data and those of a three-dimensional (3D) model, except for the shear stresses and turbulent kinetic energy. In general, quantitative comparison with the experimental data has revealed that, by applying proper models of inter-phase momentum transfer, and performing simulations based on the two-fluid model, satisfactory predictions of mean flow quantities can be obtained for this application away from the injector.