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动力学 4

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Simulation of bubble column reactors using CFD coupled with a population balance model

Tiefeng WANG

《化学科学与工程前沿（英文）》 2011年第5卷第2期页码 162-172 doi: 10.1007/s11705-009-0267-5

摘要： Bubble columns are widely used in chemical and biochemical processes due to their excellent mass and heat transfer characteristics and simple construction. However, their fundamental hydrodynamic behaviors, which are essential for reactor scale-up and design, are still not fully understood. To develop design tools for engineering purposes, much research has been carried out in the area of computational fluid dynamics (CFD) modeling and simulation of gas-liquid flows. Due to the importance of the bubble behavior, the bubble size distribution must be considered in the CFD models. The population balance model (PBM) is an effective approach to predict the bubble size distribution, and great efforts have been made in recent years to couple the PBM into CFD simulations. This article gives a selective review of the modeling and simulation of bubble column reactors using CFD coupled with PBM. Bubble breakup and coalescence models due to different mechanisms are discussed. It is shown that the CFD-PBM coupled model with proper bubble breakup and coalescence models and interphase force formulations has the ability of predicting the complex hydrodynamics in different flow regimes and, thus, provides a unified description of both the homogeneous and heterogeneous regimes. Further study is needed to improve the models of bubble coalescence and breakup, turbulence modification in high gas holdup, and interphase forces of bubble swarms.

关键词： bubble column computational fluid dynamics bubble breakup and coalescence population balance model bubble size distribution

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Numerical simulation of micro scale flowing and boiling

Wen WANG, Rui ZHUAN,

《能源前沿（英文）》 2009年第3卷第4期页码 396-401 doi: 10.1007/s11708-009-0049-2

摘要： Numerical simulations of flowing and boiling in micro channels are presented, including the modeling of bubble dynamics of nucleate boiling, and a description of the interface of two phases with the volume-of-fluid (VOF). The two calculated cases are compared with related experimental data in literature. Some simulated results are found corresponding well to the experimental data. The simulated results also show the details of 3-dimensional heat transfer and the flow in micro channels, which are helpful to the investigation of the mechanism of two-phase heat transfer and flow in micro channels.

关键词： volume-of-fluid (VOF) micro channel nucleate boiling bubble dynamics simulation

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Nucleate boiling in two types of vertical narrow channels

Lei GUO, Shusheng ZHANG, Lin CHENG

《能源前沿（英文）》 2011年第5卷第3期页码 250-256 doi: 10.1007/s11708-010-0128-4

摘要： To explore the mechanism of boiling bubble dynamics in narrow channels, we investigate 2-mm wide I- and Z-shaped channels. The influence of wall contact angle on bubble generation and growth is studied using numerical simulation. The relationships between different channel shapes and the pressure drop are also examined, taking into account the effects of gravity, surface tension, and wall adhesion. The wall contact angle imposes considerable influence over the morphology of bubbles. The smaller the wall contact angle, the rounder the bubbles, and the less time the bubbles take to depart from the wall. Otherwise, the bubbles experience more difficulty in departure. Variations in the contact angle also affect the heat transfer coefficient. The greater the wall contact angle, the larger the bubble-covered area. Therefore, wall thermal resistance increases, bubble nucleation is suppressed, and the heat transfer coefficient is lowered. The role of surface tension in boiling heat transfer is considerably more important than that of gravity in narrow channels. The generation of bubbles dramatically disturbs the boundary layer, and the bubble bottom micro-layer can enhance heat transfer. The heat transfer coefficient of Z-shaped channels is larger than that of the I-shaped type, and the pressure drop of the former is clearly higher.

关键词： nucleate boiling narrow channel numerical simulation bubble dynamics

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Experimental study on bubble behavior and CFD simulation of large-scale slurry bubble column reactor

Haoyi SUN, Tao LI, Weiyong YING, Dingye FANG

《化学科学与工程前沿（英文）》 2010年第4卷第4期页码 515-522 doi: 10.1007/s11705-010-0516-7

摘要： Slurry bubble column reactors (SBCR) is a three-phase fluidized reactor with outstanding advantages compared with other reactors and is difficult to scale-up due to lack of information on hydrodynamics and mass transfer over a wide range of operating conditions of commercial interest. In this paper, an experiment was conducted to investigate the bubble behavior in SBCR with a height of 5600 mm and an interior diameter of 480 mm. Bubble rise velocity, bubble diameter, and gas holdup in different radial and axial positions are measured in SBCR using four-channel conductivity probe. Tap water, air, and glass beads (mean diameter 75–150 μm) are used as liquid, gas, and solid phases, respectively. It shows that hydrodynamic parameters have good regularity in SBCR. Moreover, a commercial computational fluid dynamics (CFD) package, Fluent, was used to simulate the process in SBCR. The simulations were carried out using axi-symmetric 2-D grids. Data obtained from experiment and CFD simulation are compared, and results show that the tendency of simulation is almost uniform with the experiment, which can help to obtain further understanding about multiphase flow process and establish a model about the synthesis of alcohol ether fuel in SBCR.

关键词： SBCR four-channel conductivity probe hydrodynamics CFD

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Experimental study on the stratum applicability and mechanisms of bubble–slurry for earth pressure balance

《结构与土木工程前沿（英文）》页码 1387-1399 doi: 10.1007/s11709-023-0005-y

摘要： Soil conditioning is essential for addressing the stratum applicability problem of earth pressure balance (EPB) shields. Under high water pressures, EPB shields spew water and soil when excavating coarse-grained strata. Typically, foam combined with polymers and slurry is used to solve spewing. However, in current techniques, slurry, foam, and the other agents are mixed with soil separately, their synergistic effect is seldom realized. In this study, an anionic surfactant was used to foam in bentonite slurry to form bubble–slurry to maximize the synergy between bubbles and slurry. The slump, volume stability, and permeability test of bubble–slurry-conditioned sand was conducted to examine the conditioning effect, and the stratum applicability of bubble–slurry was determined from the perspective of permeability. It was found that the conditioning effect of bubble–slurry in coarse gravel soil was excellent and could expand the applicability of EPB shields. The main stabilization mechanism of bubble–slurry is that bentonite particles provide a space barrier for bubbles. And three seepage modes of bubble–slurry-conditioned sand were innovatively defined, and the occurrence conditions of the three seepage modes were analyzed according to the permeability coefficient of sand, initial dynamic shear force of bubble–slurry, and hydraulic gradient.

关键词： EPB shield bubble–slurry soil conditioning stability permeability

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钢筒内衬爆炸水井设计中的几个动力学问题研究

顾文彬,陈学平,刘建青

《中国工程科学》 2013年第15卷第10期页码 71-79

摘要：

以3 kg 2，4，6-三硝基甲苯（TNT）炸药在内径和深度均为11 m的内衬钢筒混凝土围堰爆炸水井中的爆炸为研究对象，数值模拟研究了筒壁厚度、混凝土围堰厚度对钢筒受力与变形的影响，以及水井内设置气泡帷幕对提高设施安全性等爆炸水井设计中关注的几个动力学问题。结果表明：水井内水中爆炸冲击波参数与P. Cole公式计算结果基本吻合；钢筒内壁不利的受力与形变部位都出现在装药中心水平线以下的筒体部位，直到壁厚达到50 mm时距筒底1.60 m处等效塑性应变仍可达到0.001 6，不满足强度理论判断条件；取钢筒厚度为20 mm，外加0.5 m厚混凝土围堰时，内衬钢筒爆炸水井符合安全性强度设计要求；在水井底部设置半径为4.9 m、厚度为0.05 m气泡帷幕时，可使筒壁处的冲击波压力峰值降低40.6 %；对于壁厚为20 mm的钢筒，采用气泡帷幕衰减冲击波措施时，混凝土围堰厚度达到0.35 m就能满足安全性设计要求。上述结论可为内衬钢筒爆炸水井结构设计和安全性评估提供方法及依据。

关键词：内衬钢筒爆炸水井设计动力学分析应力应变响应数值模拟研究气泡帷幕混凝土围堰

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The role of single deformed bubble on porous foam tray with submerged orifices on the mass transfer enhancement

《化学科学与工程前沿（英文）》 2023年第17卷第12期页码 2127-2143 doi: 10.1007/s11705-023-2363-3

摘要： Foam trays with porous submerged orifices endow bubbles uniformly distributed, which are considered attractive column internals to enhance the gas-liquid mass transfer process. However, its irregular orifice and complex gas-liquid flow make it lack pore-scale investigations concerning the transfer mechanism of dynamic bubbling. In this work, the actual porous structure of the foam tray is obtained based on micro computed tomography technology. The shape, dynamic, and mass transfer of rising bubbles at porous orifices are investigated using the volume of fluid and continue surface force model. The results demonstrate that the liquid encroaching on the gas channels causes the increasing orifices velocity, which makes the trailing bubble easily detach from the midst of the leading bubble and causes pairing coalescence. Additionally, we found that the central breakup regimes significantly improve the gas-liquid interface area and mass transfer efficiency. This discovery exemplifies the mechanism of mass transfer intensification for foam trays and serves to promote its further development.

关键词： bubble formation porous submerged orifices process intensification foam tray

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Synchronous observation of rising soluble bubble through quiescent solution

Yifu ZHANG , Shuai TIAN , Weizhong LI , Yongchen SONG ,

《能源前沿（英文）》 2009年第3卷第3期页码 307-312 doi: 10.1007/s11708-009-0028-7

摘要： An experimental method using computer image processing technology (CIPT) was proposed to observe and investigate the velocity, deformation, heat and mass transfer, etc. of a rising soluble gas (CO) bubble through a quiescent hot water. A model was set up to describe the behavior of the bubble in a visual experimental system in which a high-speed camera rose instantaneously with the movement of the bubble. A series of trajectory videos about the bubble were recorded by a computer linked to the camera. The trajectory, volume changes and rate of mass transfer of the bubble were obtained by the CIPT. It is found that the single bubble follows a rolling trajectory at the initial stage when there is mass transfer. With the volume decreasing, the disturbed behavior of the bubble becomes tempered. When the rising velocity of the bubble reaches the maximum, the velocity is nearly at a constant. The experimental and analysis results show that this method is useful for the research on the mass transfer and the movement of rising bubbles in liquid.

关键词： soluble bubble mass transfer synchronous observation computer image processing

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Study on direct alcohol/ether fuel synthesis process in bubble column slurry reactor

Zhen CHEN, Haitao ZHANG, Weiyong YING, Dingye FANG

《化学科学与工程前沿（英文）》 2010年第4卷第4期页码 461-471 doi: 10.1007/s11705-010-0517-6

摘要： The recent studies of direct alcohol/ether synthesis process in slurry reactors were reviewed, and the research work in our laboratory was carried out in this paper. a global kinetics model for direct dimethyl ether (DME) synthesis from syngas over a novel Cu-Zn-Al-Zr slurry catalyst was established according to the total of 25 experimental data, and a steady-state one-dimensional mathematical model was further developed in bubble column slurry reactor (BCSR), which was assumed that the bubble phase was plug flow, and the liquid phase was fully mixed flow. The numerical simulations of reactor design of 100000 t/a dimethyl ether pilot plant indicate that higher pressure and lower temperature were favorable to the increase of CO conversion, selectivity of dimethyl ether, product yield and height of slurry bed. The optimal operating conditions for DME synthesis process were obtained: reaction temperature at 240°C, reactor pressure at 5 MPa and reactor diameter of 2.5 m.

关键词： syngas alcohol/ether fuel slurry catalyst bubble column slurry reactor global kinetics mathematical model

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Investigation of bubble diameter and flow regime between water and dilute aqueous ethanol solutions in

Baharak SAJJADI, Mostafa Keshavarz MORAVEJI, Reza DAVARNEJAD

《化学科学与工程前沿（英文）》 2011年第5卷第2期页码 194-202 doi: 10.1007/s11705-010-1019-2

摘要： In this study, the effect of ethanol addition into pure water and its concentration on bubble diameter, gas hold-up and flow regimes were investigated in an airlift reactor. Air and water with ethanol (concentration ranging from 0%–1%, v/v) were as dispersed and continuous phases, respectively. Superficial gas velocity was considered as an effective parameter. Bubble size distribution was measured by photography and picture analysis at various concentrations of ethanol and various velocities of gas. Alcohol concentration enhancement caused bubble diameter to decrease. Furthermore, the bubbles diameter in pure water was nearly 4 times higher than that of ethanol with concentration of 1% (v/v) and also was 3.4 times higher than that of ethanol with concentration of 0.25% (v/v) at the highest aeration gas velocity inlet. For ethanol solutions in lower superficial gas velocity, a homogenous flow regime was observed. This trend continued to inlet gas velocity of about 0.4 cm/s. The transition flow regime occurred after this datum although in pure water, a homogenous flow regime was observed up to a superficial gas velocity of 0.7 cm/s. The gas hold-up in dilute ethanol solutions were more than (around 2 times) that of pure water and increased with increasing concentration of ethanol in those solutions.

关键词： airlift rector bubble diameter gas hold-up flow regime ethanol

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Feasibility of bubble surface modification for natural organic matter removal from river water using

Yulong Shi, Jiaxuan Yang, Jun Ma, Congwei Luo

《环境科学与工程前沿（英文）》 2017年第11卷第6期 doi: 10.1007/s11783-017-0954-2

摘要： A novel, functionalized bubble surface can be obtained in dissolved air flotation (DAF) by dosing chemicals in the saturator. In this study, different cationic chemicals were used as bubble surface modifiers, and their effects on natural organic matter (NOM) removal from river water were investigated. NOM in the samples was fractionated based on molecular weight and hydrophobicity. The disinfection byproduct formation potentials of each fraction and their removal efficiencies were also evaluated. The results showed that chitosan was the most promising bubble modifier compared with a surfactant and a synthetic polymer. Tiny bubbles in the DAF pump system facilitated the adsorption of chitosan onto microbubble surfaces. The hydrophobic NOM fraction was preferentially removed by chitosan-modified bubbles. Decreasing the recycle water pH from 7.0 to 5.5 improved the removal of hydrophilic NOM with low molecular weight. Likewise, hydrophilic organic compounds gave high dihaloacetic acid yields in raw water. An enhanced reduction of haloacetic acid precursors was obtained with recycle water at pH values of 5.5 and 4.0. The experimental results indicate that NOM fractions may interact with bubbles through different mechanisms. Positive bubble modification provides an alternative approach for DAF to enhance NOM removal.

关键词： Bubble surface modification Chitosan Disinfection by-product Dissolved air flotation Organic fraction

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Computational fluid dynamics simulation of aerosol transport and deposition

Yingjie TANG, Bing GUO

《环境科学与工程前沿（英文）》 2011年第5卷第3期页码 362-377 doi: 10.1007/s11783-011-0365-8

摘要： In this article computational fluid dynamics (CFD) simulation of aerosol transport and deposition, i.e. the transport and deposition of particles in an aerosol, is reviewed. The review gives a brief account of the basics of aerosol mechanics, followed by a description of the general CFD approach for flow field simulation, turbulence modeling, wall treatments and simulation of particle motion and deposition. Then examples from the literature are presented, including CFD simulation of particle deposition in human respiratory tract and particle deposition in aerosol devices. CFD simulation of particle transport and deposition may provide information that is difficult to obtain through physical experiments, and it may help reduce the number of experiments needed for device design. Due to the difficulty of describing turbulent flow and particle-eddy interaction, turbulent dispersion of particles remains one of the greatest challenges for CFD simulation. However, it is possible to take a balanced approach toward quantitative description of aerosol dispersion using CFD simulation in conjunction with empirical relations.

关键词： computational fluid dynamics (CFD) aerosol transport deposition

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Development of electrorheological chip and conducting polymer-based sensor

Xianzhou ZHANG, Weihua LI, Weijia WEN, Yanzhe WU, Gordon WALLACE,

《机械工程前沿（英文）》 2009年第4卷第4期页码 393-396 doi: 10.1007/s11465-009-0043-8

摘要： This paper presents the development of an integrated sensor using two types of smart materials: electrorheological (ER) fluids and conducting polymers (CPs). The developed ER chip worked as an actuator, and it was driven by different voltages and control frequencies. When the four electrodes are controlled synchronously, the diaphragm acts as a vibrator whose frequency can be adjusted in accordance with the frequency of the electrical signals. The response signals of the CP sensor were recorded, and its properties were analyzed. Experimental results show that the amplitude decreases monotonically when the frequency increases, owing to the time delay in the pressure buildup in the ER chip. However, the displacement fluctuation of the diaphragm below 20Hz can be detected clearly even if the value is very low. When the vibration frequency is larger than 20Hz, the CP sensor can hardly detect the displacement fluctuation. Thus, the upper limit frequency that the CP sensor can detect is about 20Hz. The practical applications of this microdevice are also discussed.

关键词： electrorheological (ER) fluids conducting polymer (CP) polydimethylsioxane (PDMS) driving frequency amplitude bubble counter

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Recent developments in passive interconnected vehicle suspension

Wade A. SMITH, Nong ZHANG,

《机械工程前沿（英文）》 2010年第5卷第1期页码 1-18 doi: 10.1007/s11465-009-0092-z

摘要： This paper presents an overall review on the historical concept development and research advancement of passive hydraulically interconnected suspension (HIS) systems. It starts with an introduction to passive HIS systems and their various incarnations developed over many decades. Next, a description is provided of a recently proposed multidisciplinary approach for the frequency-domain analysis of vehicles fitted with an HIS. The experimental validation and applications of the method to both free and forced vibration analysis are discussed based on a simplified, roll-plane half-car model. A finite-element-method-based approddach for modelling the transient dynamics of an HIS vehicle is also briefly outlined. In addition, recent work on the investigation of NVH associated with HIS-equipped vehicles is mentioned. Discussion is then provided on future work to the further understanding of HIS and its applications. The paper concludes that interconnected suspension schemes can provide much greater flexibility to independently specify modal stiffness and damping parameters – a characteristic unique among passive suspensions. It points out that there is a need for system optimisation, and there are troublesome NVH issues that require solutions. It suggests that further research attention and effort be paid to NVH issues and system level optimisation to gain a greater understanding of HIS and to broaden its applications.

关键词： interconnected suspensions rollover prevention vehicle dynamics ride comfort multibody system dynamics hydraulic system dynamics

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Nonlinear dynamics of a wind turbine tower

A. GESUALDO, A. IANNUZZO, F. PENTA, M. MONACO

《机械工程前沿（英文）》 2019年第14卷第3期页码 342-350 doi: 10.1007/s11465-019-0524-3

摘要： The recent proliferation of wind turbines has revealed problems in their vulnerability under different site conditions, as evidenced by recent collapses of wind towers after severe actions. Analyses of structures subjected to variable actions can be conducted through several methods with different accuracy levels. Nonlinear dynamics is the most reliable among such methods. This study develops a numerical procedure to obtain approximate solutions for rigid-plastic responses of structures subjected to base harmonic pulses. The procedure’s model is applied to a wind turbine tower subjected to inertial forces generated by harmonic ground acceleration, and failure is assumed to depend on the formation of shear hinges. The proposed approach provides an efficient representation of the post-elastic behavior of the structure, has a low computational cost and high effectiveness, and uses a limited number of mechanical parameters.

关键词： nonlinear dynamics plastic shear failure modal approximation time history