层析成像技术在多相流检测中的应用

介绍了流动层析成像技术的一般概念。综述了Ｘ射线、γ射线、中子射线、超声波和电容等５大类流动层析成像技术的发展现状，最后论述了该项技术的发展趋势和工业应用前景。     

电阻层析成像技术测量两相流气相流量

提出利用双截面电阻层析成像(ERT)系统,并采用相关方法进行两相流气相流量的测量。介绍像素相关与基于边界电压特征值相关两种相关方法,并进行单气泡模拟实验。实验结果表明用这两种相关方法进行两相流的气相流量测量是可行的。     

应用电容层析成像对多相流的动态可视化(英文)

Identifying the flow patterns is vital for understanding the complicated physical mechanisms in multiphase flows.For this purpose,electrical capacitance tomography(ECT) technique is considered as a promising visualization method for the flow pattern identification,in which image reconstruction algorithms play an important role.In this paper,a generalized dynamic reconstruction model,which integrates ECT measurement information and physical evolution information of the objects of interest,was presented.A generalized objective functional that simultaneously considers the spatial constraints,temporal constraints and dynamic evolution information of the objects of interest was proposed.Numerical simulations and experiments were implemented to evaluate the feasibility and efficiency of the proposed algorithm.For the cases considered in this paper,the proposed algorithm can well reconstruct the flow patterns,and the quality of the reconstructed images is improved,which indicates that the proposed algorithm is competent to reconstruct the flow patterns in the visualization of multiphase flows.     

采用电阻层析成像技术测量气液加压鼓泡塔局部气泡参数

在内径0.3 m,高6.6 m的加压气液鼓泡塔反应器中,采用电阻层析成像技术(ERT)研究了空气-水体系中气泡群平均上升速度、局部气含率及其径向分布。在表观气速0.119~0.312 m s 1,压力0.5~2.0 MPa,考察了表观气速、压力对气泡群上升速度、局部气含率及其径向分布的影响。实验结果表明,鼓泡塔中局部气含率随着表观气速与压力的增大而增大,其径向分布呈现出中心高边壁低的分布特征,但整个截面的分布并非严格对称,在r/R=0~0.3,气含率变化较小,且极大值出现在该范围内;气泡群的局部上升速度随着表观气速的增大而增大,但是随着压力的增大而减小。     

气固多相双通道同轴射流湍流场的数值模拟(1)

以气体湍流运动方程组、ｋε双方程湍流模型及颗粒群运动的轨道模型为基础,气体湍流场的计算采用ＳＩＭＰＬＥ数值计算方法,颗粒群的运动方程采用ＲｕｎｇｅＫｕｔａ方法求解,开发研制出相应的通用计算软件,可以理论模拟预测工程气固流动中的气体湍流场的速度分布、颗粒运动速度场及颗粒的空间运动轨迹等。     

气固多相双通道同轴射流湍流场的数值模拟(2)

运用气固多相流数值模拟软件对双通道同轴气固射流湍流场进行了数值模拟研究,预测结果与ＬＤＶ激光测速仪测得的固体颗粒速度分布值进行了比较,结果表明,吻合较好,该软件为气固多相流工程设备的快速、经济的开发研究提供了相应的辅助工具,同时,也是理论研究气固多相化学反应流的基础。     

基于声发射技术的垂直管气液两相流动检测方法

声发射(AE)作为一种无损检测手段,用于气液两相流的测量具有非侵入式、测量不破坏被测管道及流场分布,信号强、灵敏度高等优点。利用声发射技术在河北大学垂直管气液两相流管道上进行了大量实验,运用现代信息数据处理方法对气液两相流垂直管道流型特征参数进行了提取。分析结果表明利用声发射手段提取出的流型特征参数可以反映出典型流型下的动力学特征。垂直管道中,泡状流、弹状流、环状流以及过渡状态下的乳沫状流在时域和频域信号中有着明显区别,小波能量和小波包分解后的信息熵的值也存在较大的差异性,从另一角度验证了在不同流型下两相流体在管道内部不同的运动状态,利用模式识别的思想,对垂直管4种典型流型进行了流型识别,取得了较好的效果,研究结果表明声发射技术可以作为一种技术手段用于气液两相流流动的检测。     

基于声发射技术的垂直管气液两相流动检测方法

声发射（AE）作为一种无损检测手段,用于气液两相流的测量具有非侵入式、测量不破坏被测管道及流场分布,信号强、灵敏度高等优点。利用声发射技术在河北大学垂直管气液两相流管道上进行了大量实验,运用现代信息数据处理方法对气液两相流垂直管道流型特征参数进行了提取。分析结果表明利用声发射手段提取出的流型特征参数可以反映出典型流型下的动力学特征。垂直管道中,泡状流、弹状流、环状流以及过渡状态下的乳沫状流在时域和频域信号中有着明显区别,小波能量和小波包分解后的信息熵的值也存在较大的差异性,从另一角度验证了在不同流型下两相流体在管道内部不同的运动状态,利用模式识别的思想,对垂直管4种典型流型进行了流型识别,取得了较好的效果,研究结果表明声发射技术可以作为一种技术手段用于气液两相流流动的检测。     

固-液/气-液多相耦合热控技术应用研究进展

相变热控技术具有设备性能可靠、质量轻、耗能低等优点,在工业和学术界受到广泛关注。利用固-液相变恒温吸热和气-液相变超高导热特性,可实现多相耦合的高效储热传热过程。本文针对固-液/气-液多相耦合热控技术提出多相耦合概念,以典型相变材料和热管耦合系统为切入点,首先介绍相变及多相耦合的工作原理,归纳了两者之间的典型耦合方式：相变材料分别置于热管蒸发段、冷凝段、绝热段,或热管整体嵌入相变材料作为导热骨架;然后着重评述了目前国内外多相耦合热控技术用于电子器件冷却和电池热管理领域的研究进展,并对其他领域（如蓄热/冷）的应用现状进行总结;最后从材料改性、器件耦合、系统协同等角度提出当前面临的问题和未来发展方向。     

计算机层析成像技术及其在化工多相流测量中的应用

介绍了射线、电容、电阻和超声波4种计算机层析成像技术的测量原理和在化工多相流测量中的应用,并讨论了它们的发展现状及存在的一些问题。     

Examination of swirling flow using electrical resistance tomography

Swirling flow within pipeline systems has significant industrial applications such as the suspension of particles at lower pumping power, improved particle mixing and the reduced erosion of pipeline bends due to slurries. However, the detection and analysis of swirling solids using technologies such as laser Doppler anemometry is expensive and of limited value in opaque fluids. In this paper, a novel and cheaper electrical resistance tomography (ERT) system is used to examine swirling flow of plastic beads and quartzite over four planes in a horizontal pipeline system. The resulting images are further rendered into three dimensions whereby the swirling bulk-solid motion is clearly evident. This new technology and the resultant 3D visualisations have potential to enable improved analysis of swirling flow as well as to identify areas of erosion in pipeline systems. Through this, greater understanding of multiphase systems should be attained, providing information to advance modelling of fluid behaviour.     

Electrical resistance tomography (ERT) for flow and velocity profile measurement of a single phase liquid in a horizontal pipe

Electrical resistance tomography (ERT) is a novel, simple, and robust method of process imaging which uses non-invasive sensors located on the periphery of vessels to reconstruct a cross-sectional image of the vessel interior. This method of imaging when conducted on two adjacent planes on a pipe provides the ability to extract flow information. Previous studies have investigated this application on multi-phase flows in which the secondary phase provided the required pulse conductivity variation. In these studies the velocity profile and flow regime were identified using the common cross-correlation technique.     

Electrical Resistance Tomography (ERT) applications to Chemical Engineering

Electrical Resistance Tomography (ERT) has the capability of offering time-evolving multidimensional comprehensive process knowledge, enrichment of fundamental process understanding and enhancement of the design and operation of process equipment by measuring the conductivity distribution within a process-plant of interest. This paper reviews the wide variety of previous work on ERT applications to Chemical Engineering. The applications are categorized based on the unit operations ERT has been applied to, the media under investigation, the purpose of ERT measurements and also other technologies used in conjunction with ERT. The aim of this taxonomy is to provide the reader with a general understanding of the current situation of ERT related research and proven applications in the Chemical Engineering field and to facilitate the recognition of research gaps for future investigation. Based on this detailed taxonomy and review the potential application of ERT to the milk powder processing industry was identified. Some results of the application of ERT to milk mixing/holding tanks and milk flow pipelines for the purpose of concentration and composition measurements, detection of abnormalities and faults, and multidimensional flow and velocity profile measurements have also been presented as a case study of using this taxonomy.     

CFD数值模拟技术在液滴微流控多相流特性研究的应用进展

高集成化的微流控系统具有界面面积大、传递距离短、混合速度快等优势,已被广泛应用于许多科学领域。然而,微通道内多相流间的相互作用及动力学行为受多方面的影响,仅依靠试验观测技术和理论预测方法难以全面了解多相流传质传热过程、获取流场特性参数、揭示多相流相互作用规律。当下CFD数值模拟技术的快速发展为预测和分析微流控通道内的多相流问题提供了更为直观、有效、准确的帮助。本文对数值模拟技术在液滴微流控多相流特性研究的应用进展进行全面综述,涵盖液滴微流控装置结构及演变、液滴微流控模拟方法及优化以及微通道内多相流作用过程及原理。     

Application of electrical resistance tomography on liquid-solid two-phase flow characterization in an LSCFB riser

The application of liquid-solid circulating fluidized beds (LSCFB) is steadily increasing in the chemical, biochemical and other industries. Electrical resistance tomography (ERT) as an imaging technique was employed for the study of flow parameters such as phase holdup, velocity distribution of individual phases in LSCFB. ERT is a non-invasive technique based on conductivity measurement of the continuous phase, which also provides color-coded cross-sectional view of phases with a frequency of up to 250 images per second. The local conductivity measured by a number of electrodes located at the periphery of the plane was then further converted into a local phase concentration distribution based on Maxwell's relation. Local solids holdup also measured by using optical fibre probe to compare and verify the result obtained by ERT. By cross-correlation between the data obtained from a pair of planes of ERT, one upstream and one downstream, the phase propagation velocity was determined. Water was used as the continuous and conductive phase and glass beads and lava rocks (LR) of 500 μm sizes were used as the solid and non-conductive phase in this investigation. Radial non-uniformity of phase holdups was observed at different superficial liquid velocities. Solids holdup was higher in regions close to the wall and low in the central area. Such non-uniformity in phase holdup decreased with increasing liquid velocity. Both solids holdup and radial non-uniformity increased with superficial solids velocity. The solids propagation velocity increased in the central region under different superficial liquid velocities. Good agreement was observed between the data obtained from the two methods.     

Dynamic and local gas holdup studies in external loop recirculating airlift reactor with two rolls of fiberglass packing using electrical resistance tomography

BACKGROUND: Airlift bioreactors have been used extensively in biotechnology industries in recent years in a variety of arrangements and applications. The insertion of packing inside the bioreactors has the potential to provide high productivity within a compact size through utilizing immobilized species. RESULTS: A novel recirculating external loop airlift bioreactor that has two rolls of fiberglass packing and a gas distributor in between was designed and built. Electrical resistance tomography (ERT) images showed that the gas holdup increased after installing the packing and the gas distributor. Gas holdup in the riser increased with decreasing static liquid height in the bioreactor. This decreased the liquid superficial velocity, which contributed to a higher gas holdup in the bioreactor. Results also showed that riser gas holdup varied slightly with different sparger configurations. Higher gas holdup increases the oxygen mass transfer rate by increasing the residence time and interfacial mass transfer area. CONCLUSION: ERT results showed that fiberglass packing with an installed gas distributor in bioreactors can achieve higher gas holdup at higher superficial gas velocity. This can contribute to improved conversion in bioreactors with packing through utilizing higher biomass concentrations and higher oxygen concentration. © 2012 Society of Chemical Industry     

Study of the swirling flow field induced by guide vanes using electrical resistance tomography and numerical simulations

In this work, the swirling flow field induced by guide vanes was studied using electrical resistance tomography (ERT) and numerical simulations. The results show that the two-phase water and oil mixture moves in the same axial direction for this type of flow field, which is very unlike the flow behavior of a traditional hydrocyclone with a tangential inlet. In the pipe behind the guide vanes, the smallest axial velocity and tangential velocity are located at the center of the pipe. From the pipe center to the pipe wall, both pressure and velocity increase gradually. Downstream of guide vanes, the maximal oil volume fraction is observed at the center of the pipe. From the center of the pipe to the inner wall, the oil volume fraction gradually decreases. Moreover, ERT can precisely show the oil distribution in the pipe section. These studies prove the possibility of efficient oil and water mixture separation by guide vanes, and the results may be very important for guiding the optimal design of vane-type pipe separators.     

多相/多组分LBM模型及其在微流体领域的应用

多相/多组分流体在化工领域中广泛应用,通常伴随有组分传递、相变、界面的产生与运动、化学反应等复杂的物理、化学过程,建立描述相应复杂体系的理论模型和模拟方法面临着极大的挑战。格子Boltzmann方法（lattice Boltzmann method,LBM）是近年来备受关注的一种介观模拟方法;多相/多组分格子Boltzmann模型具有易于追踪多相动态界面、壁面性质设定简单等优点,从物理模型到计算精度和速度都有很大的优势,尤其适合于模拟微化工系统下的多相多组分流动问题。以格子Boltzmann方法为基础,重点介绍了气液及液液体系多相/多组分LBM模型的研究进展以及其在微流体系统中的应用。     

Dimensional similitude for scale-up of hydrodynamics in a gas-liquid-(solid) EL-ALR

This study tests the scaling approach for gas-liquid-(solid) external loop airlift reactor (EL-ALR) hydrodynamics based upon geometric and dynamic similitude with a limited number (6) of dimensionless groups. A sixth dimensionless group for sparger characteristic (Scp) is developed. Scp is a convenient parameter to characterize fluid flow performance of EL-ALR and a large cold-flow 0.86 m diameter column. To our knowledge, there is more ambiguity concerning its definition for EL-ALR and a large cold-flow 0.86 m diameter column especially when different sparger structures are used. In this study, reliability of the modified Reynolds and Scp are proposed for such an EL-ALR and a large cold-flow 0.86 m diameter column used different sparger structures. The Scp is based on the pitch and angle between hole normal vector and horizontal line as the characteristic parameters. Experiments were carried out in two systems in which all six dimensionless groups were matched: a 55 wt% aqueous glycerol solution with ceramic catalyst particles in an industrially operated large cold-flow 0.86 m diameter column (system 1) and silicone oil with cylindrical aluminum particles in Taishan Scholar Lab (TSL) EL-ALR with a riser (0.47 m diameter and 2.5 m height) and two downcomers (0.08 m diameter and 2.5 m height) (system 2) with air as the gas in both cases. The micro-conductivity probe and the 3D Laser Doppler Anemometer (LDA) techniques were, respectively, implemented to measure local gas holdup (α_Gr) and Peclet number (Pe) in the riser over a wide range of operation conditions. Although Peclet number was slightly different for the two systems, trends were similar. Gas holdups were always slightly higher for system 1. The dimensionless transition velocities from dispersed to coalesced flow were similar. Differences between the two systems are significant, but generally less than 15%, so the dimensionless similitude approach gives a reasonable basis for estimating global hydrodynamic parameters under the present operating conditions. The differences between the two systems are attributed to the complex coalescence behavior of liquid mixtures and the different sparger structures chosen, suggesting that additional dimensionless groups are needed to fully characterize the local dynamic bed behavior. This agreement proves that the proposed modified dimensionless numbers can be well adapted for engineering purposes and used to compare the flow performance between the two systems.     

Radial nonuniformity index (RNI) in fluidized beds and other multiphase flow systems

The radial nonuniformity index (RNI) is a new non‐dimensional index recently devised to quantify the extent of radial variations of flow parameters in fluidized beds and other multiphase flow systems. The index, defined as the ratio of the standard deviation of the given flow parameter in the radial direction to the maximum practically possible standard deviation of that particular parameter, is shown to be an excellent measure of the radial flow structure. This index allows the use of a single value to summarize the radial variation of a given flow parameter. The higher the value of the RNI the less uniform is the flow, and vice versa. Using this technique, radial distributions of local solids concentration and particle velocities from different circulating fluidized bed systems (gas‐solid and liquid‐solid, upflow and downflow) were examined. It has been found that the RNI can be confidently related to the flow conditions in the circulating fluidized beds, and more insight understanding has been achieved.