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The two‐phase flow pattern for air‐water mixtures inside a 6.9 mm U‐tube is reported to have curvature ratios of 3?7.1. At a lower total mass flux of 50 kg/m2·s and a quality of 0.1, or at a larger curvature ratio of 7.1, no influence on the flow patterns is seen. However, if the curvature ratio is reduced to 3, the flow pattern in the recovery region just after the return bend is temporally turned from stratified flow into annular flow. For a quality larger than 0.4, the annular flow pattern prevails in the entire tube. For G = 400 kg/m2·s and x < 0.01, the size of the plug in the downstream is usually larger than that in the upstream due to the coalesce in the return bend. This coalescence phenomenon continues to further increase the total mass flux at the lower quality region. For a total mass flux above 500 kg/m2·s, the bubbly flow pattern in the upstream region may become intermittent. 相似文献
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The gas/solid flow characteristics in a circulating fluidized bed with two different inlet configurations were investigated by numerical simulation based on an Eulerian approach. In order to describe the interaction between the gas phase and the solid phase and the influence of the solid phase on the gas turbulence, a source term formulation with a more reasonable physical meaning was introduced. The simulation results were validated by the experimental data; then, the model was employed to examine the effect of the inlet configuration on the gas and solid feeding. The simulation results showed that, using the side feeding system, the distributions of solid flow and concentration were highly variable both over the column cross‐section and along the column height. However, such variations can be improved by using the elbow inlet system where the gas and solid are fed from the bottom. 相似文献
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Sumana Ghosh Gargi Das Prasanta Kumar Das 《Chemical Engineering Research and Design》2011,89(11):2244-2253
The present work reports a computational fluid dynamic analysis of core annular flow through return bends. Core annular flow of lubricating oil and water has been simulated using FLUENT 6.3.26. A satisfactory trend matching is observed between numerically obtained phase distribution and experiments. A comprehensive study has been made to generate the profiles of velocity, pressure, and volume fraction over a wide range of oil and water velocities. It has been observed that the oil core may foul the bend wall under certain operating conditions. Through computational simulations the operating zone safe from the risk of fouling has also been identified. 相似文献
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提出了一个概念合理、预测性能好的两通道模型，描述垂直向上气固流动系统的环／核内循环流动结构。基于气固相互作用最少及质量、动量守恒原理，确定了气固两相流动状态、计算结果（如预测核心区半径、核心区及环形区内空隙率、气体速度、颗粒速度及其轴向分布等）合理，且与实验结果有良好的一致性。该模型还可以用于预测在两通道内的曳力系数，气、固返混以及两区间质量交换速率等，对反应器设计具有一定参考价值。 相似文献
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为克服管壁取样测量气液两相流体流量方法中环状流不均匀稳定的缺点,在旋流叶片下游采用整流元件将旋流形成的环状流整改成液膜厚度均匀稳定的环状流型,增强取样的代表性,并在整流器下游增设了两个取样位置,以确定装置最佳取样位置。分析表明,在取样位置1处形成的环状流比较均匀稳定;随着流量的增大,均匀环状流稳定流动的时间延长。本实验装置存在最小正常工作范围：气相折算速度为30.50 m/s,液相折算速度为0.08 m/s。当流量超过这一特定值时,流型整改效果良好。 相似文献
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Hui Lu Hai‐Feng Liu Wei‐Feng Li Jian‐Liang Xu 《American Institute of Chemical Engineers》2013,59(6):1882-1893
An annular granular jet surrounding an air jet at its core is studied experimentally using high‐speed digital photography. The experimental results show that particle bubbles in a periodic manner are formed whether the central air is swirling or not. This flow feature is induced by the intense interaction between the central air jet and the annular granular jet, and it is important for the dispersion of particles by the air jet in the near field. The interaction between the two phases is mainly intensified by higher superficial air jet velocity and the addition of swirl to the central air jet. The bubbling frequency, bubble size, bubble shape, and bubble growth rate are investigated by analyzing a large number of images. In addition, the dispersion angle of granular jet is found to be mainly governed by the radial growth rate of the bubble. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1882–1893, 2013 相似文献
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S. S. Pandiella L. A. Garcí a M. Dí az C. Webb 《Chemical Engineering Communications》1999,173(1):197-214
When using a Computational Fluid Dynamics (CFD) code for the simulation of a two phase system, special attention must be given to the solution procedure. Fluid dynamics in CFD codes are obtained by iterative computations, and criteria must be established to decide the number of iterations needed to obtain a convergent solution under certain defined conditions. In this work, the predicted liquid and gas flow patterns obtained in the simulation of hydrodynamics in bubble columns are analysed throughout the computational process, and the effects of some parameters affecting the computation are studied (dimension of the grid, working conditions, scale-up, relaxation used in the calculations, free surface performance). It was found that each of these parameters affects considerably the solution procedure (though in a different manner) and therefore no general criteria can be established to decide the number of sweeps necessary for a certain simulation. It is concluded that every simulation should be analysed individually each time the conditions are changed. This analysis clearly helps to understand the reliability of CFD predictions in complex systems. 相似文献
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During two‐phase electrolysis for hydrogen production, according with alkaline–water electrolysis process, there are bubbles which are created at electrodes which imply a great hydrodynamic acceleration in the normal earth gravity field and then a quite important electrical properties and electrochemical processes disturbance, for both transport and reaction. This disturbance can lead to the modification of the local current density and to anode effects for example. In this work, a model experimental set‐up is studied. The vertical pine electrode of small electro active surface area is surrounded with a large surface counter electrode. The hydrogen production is performed at the working electrode and effort is focused here upon the global electrochemical cell electrical performances. The polarization curves intensity vs. applied voltage are experimentally measured and presented for different factors such as: the electro active species concentration, nature and counter electrode diameter factors. © 2010 American Institute of Chemical Engineers AIChE J, 2010 相似文献
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Andhros G. Silva Deovaldo de Moraes Saleh Al Arni Carlo Solisio Attilio Converti Ricardo P. S. Oliveira Ardson S. Vianna 《化学工程与技术》2021,44(1):104-113
One of the difficulties related to oil exploration is transporting heavy oil since its high viscosity causes high‐pressure drop and energy consumption. In order to save energy, the core annular flow (CAF) can be applied where a two‐phase annular flow occurs, with peripheral water flowing offering a reduction in energy expenditure. The multiphase flow was studied experimentally in a simple purpose‐built unit. To theoretically handle the CAF, computational fluid dynamics simulations were done with the commercial package Ansys Fluent. The flow was considered turbulent, isothermal, incompressible, and 3D, and both stationary and transient cases were evaluated. The volume‐of‐fluid model was adopted for the multiphase system, and water/oil interface and turbulence phenomena were well predicted. 相似文献
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底吹气连铸中间包内气液两相流的数值模拟 总被引：5，自引：0，他引：5
以宝钢集团梅山钢厂1台连铸中间包为原型,进行底吹气中间包水模型研究. 实测结果表明,底吹气在中间包内形成\"鼓泡流\"形式的流动结构;\"鼓泡流\"的形成一方面能够破坏中间包内\"层流\"形式的短路流动,增强混合,另一方面能在中间包内形成\"气幕挡墙\",有利于夹杂物去除. 针对中间包内气-液两相\"鼓泡流\"特征,建立了底吹气中间包内气-液两相欧拉多流体模型,模型中考虑了气泡的存在对湍流增强的影响,考虑了相间滑移、气泡浮力及湍流分散力. 采用所建立的模型对底吹气中间包内气液两相流动和混合特性进行了模拟和分析,结果与水模型实测结果一致. 相似文献
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Gijs Ooms Mathieu J. B. M. Pourquie Jerry Westerweel 《American Institute of Chemical Engineers》2015,61(7):2319-2328
A numerical study has been made of laminar core‐annular through a torus. It is a follow‐up of the study by Picardo and Pushpavanam, AIChE J. 2013;59(12):4871–4886, who obtained an analytical solution for the case that the core is concentric and circular. In our study, we investigated the possibility of eccentric core‐annular flow and the deformation of the core‐annular interface. We found that a stable eccentric core position is possible, which is shifted in the direction of the inner or outer side of the torus depending on the balance of the normal stresses at the core‐annular interface. When these stresses are too far off from those for concentric and circular core‐annular flow, fouling of the wall occurs. We compared the results of core‐annular flow in a torus with those for a 90° pipe bend and found that the flow pattern in the torus is representative for the flow pattern in the bend. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2319–2328, 2015 相似文献
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A three‐dimensional oil‐water turbulent flow and oil separation process in a double‐cone liquid‐liquid hydrocyclone (LLHC) is numerically simulated using FLUENT software. The Euler‐Euler approach and Reynolds‐stress model are combined and adopted in this simulation to handle the challenging situation of anisotropic turbulent two‐phase flow with a higher volumetric ratio (over 10%) in the dispersed phase. It is visualized well in the simulation how separation, aggregation and shift of oil and water proceed in the LLHC. The oil separation efficiency is determined based on flow field and phase concentration distribution. The simulation is verified by comparing predicted and measured separation efficiency in the LLHC. 相似文献
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Our recently presented multi‐scale computational fluid dynamics (CFD) approach has proven to be able to capture the choking phenomena in a circulating fluidized bed (CFB). However, how to transfer this capability to assist industrial operation remains to be explored. To this end, this paper presents further simulation results over the intrinsic flow regime diagram and the operating diagram for gas–solid risers, showing the variation of flow regimes with gas velocity and solids flux as well as riser height. It is confirmed that the choking in CFB risers, characterized by the saturation carrying capacity and the coexistence of both dense and dilute flows, holds clear‐cut definition in hydrodynamics. In physics, both the choking, non‐choking transitions, and the critical point in‐between are intrinsic nature of gas–solid riser flows; they initiate as functions of gas velocity and solids flux. In engineering operation, however, their appearances vary with the riser height used. As a result, the intrinsic flow regime diagram can be defined by the combination of gas velocity and solids flux, although it is hard to obtain in practice owing to the limitation of riser height. The operating diagram of a CFB should be, accordingly, height‐dependent in practice, demanding the riser height as a parameter besides commonly believed gas velocity and solids flux. 相似文献
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