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Numerical study on the hydrodynamics behavior of a central insert microchannel

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Chinese Journal of Chemical Engineering 2023年第1期53卷 361-373页

作者： Yongbo Zhou Yang Jin Jun Li Qinyan Wang Ming Chen Engineering Research Center of Comprehensive Utilization and Clean Processing of Phosphorus Resources School of Chemical EngineeringSichuan UniversityChengdu 610065China

In this work, the computational fluid dynamics method is used to study the liquid hydrodynamics behavior in the microchannel without central insert(MC1) and the central insert microchannel(MC2), respectively. The maximum deviation between simulation and experiment is 24%. The formations of flow patterns are explained based on contours and force analysis where the flow pattern maps are established by two-phase flow rate. The effects of aqueous phase viscosity and two-phase flow rate on the characteristic sizes of each flow pattern are also explored. Specifically, four unconventional flow patterns are found in MC2, namely the unique droplet flow, the unique slug flow, the unique coarse annular flow and the unique film annular flow. Though the insert occupies part of the channel, the pressure difference in the channel is significantly reduced compared with MC1. Moreover, the insert significantly changes the formation velocity range of each flow pattern, greatly broadens the formation range of annular flow and also has an important influence on the characteristic size of the flow pattern. The organic-phase dimensionless axial size(Lo/W) and the dimensionless radial size(Do/W) of the droplet(slug) are negatively related to the aqueous-phase viscosity(μa) and flow rate(ua). The Do/W of the annular is negatively correlated with μaand positively correlated with organic-phase flow rate(uo). This study provides direct numerical evidence that the insert is key to the formation of bicontinuous phase flow pattern, as well as further strengthens our understanding of the flow characteristics and optimization design of insert microchannels.

关键词： Microchannel Process intensification computational fluid dynamics Liquid–liquid flow pattern Central insert

Study on the solid-liquid suspension behavior in a tank stirred by the long-short blades impeller

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Chinese Journal of Chemical Engineering 2022年第7期35卷 79-88页

作者： Zewen Chen Yongjun Wu Jian Wang Peicheng Luo School of Chemistry and Chemical Engineering Southeast UniversityNanjing 211189China Beijing System Engineering Institute Beijing 100034China CAS Key Laboratory Of Energy Regulation Materials Shanghai 200032China

We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades(LSB) impeller by the Euler granular flow model coupled with the standard k–ε turbulence model. After validation of the local solid holdup by experiments,numerical predictions have been successfully used to explain the influences of impeller rotating speed,particle density, particle size, liquid viscosity and initial solid loading on the solid suspension behavior,i.e. smaller particles with lower density are more likely to be suspended evenly in the liquid with higher liquid viscosity. At a low impeller rotating speed(N), increase in N leads to an obvious improvement in the solid distribution homogeneity. Moreover, the proposed LSB impeller has obvious advantages in the uniform distribution of the solid particles compared with single Rushton turbine(RT), dual RT impellers or CBY hydrofoil impeller under the same power consumption.

关键词： Two-phase flow computational fluid dynamics Kinetic theory of granular flow Stirred tank Long-short blades impeller

Evaluation of coarse-grained CFD-DEM models with the validation of PEPT measurements

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Particuology 2023年第11期82卷 48-63页

作者： Hanqiao Che Dominik Werner Jonathan Seville Tzany Kokalova Wheldon Kit Windows-Yule School of Chemical Engineering University of BirminghamB152TTUK School of Physics and Astronomy University of BirminghamBirminghamB152TTUK

computational fluid dynamics coupled with Discrete Element Method (CFD-DEM) is a commonly used numerical method to model gas-solid flow in fluidised beds and other multiphase systems. A significant limitation of CFD-DEM is the feasibility of the realistic simulation of large numbers of particles. Coarse-graining (CG) approaches, through which groups of multiple individual particles are represented by single, larger particles, can substantially reduce the total number of particles while maintaining similar system dynamics. As these three CG models have not previously been compared, there remains some debate, however, about the best practice in the application of CG in CFD-DEM simulations. In this paper, we evaluate the performance of three typical CG methods based on simulations of a bubbling fluidised bed. This is achieved through the use of a numerical validation framework, which makes full use of the high-resolution 3D positron emission particle tracking (PEPT) measurements to rigorously validate the outputs of CFD-DEM simulations conducted using various different coarse-graining models, and various different degrees of coarse-graining. The particle flow behaviours in terms of the particle occupancy field, velocity field, circulation time, and bubble size and velocity, are comprehensively analysed. It is shown that the CG simulation starts to fail when the size ratio between the bed chamber and the particles decreases to approximately 20. It is also observed, somewhat surprisingly, that the specific CG approach applied to interparticle contact parameters does not have a substantial effect on the simulation results for the bubbling bed simulations across a wide range of CG factors.

关键词： Coarse-graining Discrete element method computational fluid dynamics CFD-DEM Positron emission particle tracking(PEPT) Bubbling fluidised bed

Optimization of an axial coarse powder separator for low-density lignite based on the optimal seeking method

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Particuology 2023年第8期79卷 133-142页

作者： Haixia Li Zhiheng Song Anchao Zhang Zhijun Sun Leying Jin School of Mechanical and Power Engineering Henan Polytechnic UniversityJiaozuo454000China

As a major equipment for thermal power plants,the main function of coarse powder separators is to separate particles into size groups according to particle diameter.With the rising coal prices,power plants are using more low-density lignite.Consequently,the original equipment does not operate under normal conditions.Therefore,to return the equipment to normal operating conditions,the isokinetic sampling method,computational fluid dynamics(CFD),and discrete phase model(DPM)based on the Euler-Lagrange method are applied in this research to analyze the effect of baffle shapes,baffle numbers,and centrifugal blades on the equipment performance index,like R90.The shape of the baffle plate was optimized and improved.Preferential method was applied to determine the optimal number of baffles to ensure normal working conditions.Results show that curved baffles can suppress the axial negative gradient field below themselves better than rectangular baffles.The curved baffles selected by the optimal seeking method make full use of the negative axial gradient field and provide the particles entering the separation zone at tangential velocity in advance with the addition of centrifugal blades.Thus,pre-separation can be realized.The R90 is 5 at the separator outlet and 95 at the powder return port,indicating that the output capacity of the separator returned to a reasonable operating performance.

关键词： Lignite particle computational fluid dynamics Separator Optimal seeking method Isokinetic sampling

Cooling load characteristics of indoor spaces conditioned by decoupled radiant cooling unit with low radiant temperature

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Building Simulation 2022年第12期15卷 2067-2079页

作者： Yuying Liang Nan Zhang Huijun Wu Xinhua Xu Jianming Yang Gongsheng Huang Department of Architecture and Civil Engineering City University of Hong KongHong KongChina School of Civil Engineering Guangzhou UniversityGuangzhou 510006China Department of Building Environment&Energy Engineering Huazhong University of Science and TechnologyWuhanChina School of Automation Guangdong Polytechnic Normal UniversityGuangzhou 510665China

Decoupled radiant cooling units(DRCUs)are capable of increasing the cooling capacity without increasing condensation risks even using a much lower cooling temperature than conventional radiant cooling units(CRCUs).However,it is unclear whether DRCUs using low radiant cooling temperature will increase the cooling load of the conditioned indoor spaces.In this study,the cooling load characteristics of a thermal chamber conditioned by a DRCU was investigated through developing a steady-state analysis model suitable for both DRCUs and CRCUs.The total/radiative heat flux,as well as the heat exchange with a thermal manikin and walls were analysed under different surface temperatures of DRCUs.The effect of the emissivity of the thermal chamber’external wall on the cooling load was also investigated.Results indicated that the cooling load under the DRCU was slightly smaller than that under the CRCU when the same operative environment was created.Decreasing the infrared emissivity of the exterior wall’s inner surface could lead to a significant decrease in the cooling load for both the DRCU and CRCU.By decreasing the wall emissivity from 0.9 to 0.1,the total cooling load of the DRCU can be decreased by 8.4%and the heat gain of the exterior wall decreased by 21.6%.This study serves as a reference for developing the analysis model and understanding the load characteristics when DRCUs are used to create the thermal environment for indoor spaces.

关键词： radiant cooling condensation-free computational fluid dynamics cooling load hot and humid climates

Effect of impeller type and scale-up on spatial distribution of shear rate in a stirred tank

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Chinese Journal of Chemical Engineering 2022年第2期35卷 351-363页

作者： Huina Wang Xiaoxia Duan Xin Feng Zai-Sha Mao Chao Yang CAS Key Laboratory of Green Process and Engineering Institute of Process EngineeringChinese Academy of SciencesBeijing 100190China School of Chemical Engineering University of Chinese Academy of SciencesBeijing 100049China

The main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers were presented with particle image velocimetry(PIV)experiments.Not only the average shear rate in the whole tank but also the local value in the vicinity of impeller increases linearly with impeller speed.Furthermore,the shear coefficient(Ks,imp)at the impeller outlet is linearly related to the impeller flow number(Nq)and decreases with the increase of Nq in general at the constant power consumption per unit volume(Pv).During scale-up based on the constant Pv and geometric similarity,CFD results show that the volume-averaged shear rate(cavg)for RDT decreases faster than that of other impellers with the impeller tip velocity(Utip).The novel multi-blade combined(MBC)impeller with the increased height-to-diameter ratio of the stirred tank is able to more effectively improve the distribution uniformity of shear rate at the same Pv after scale-up.These studies provide a data basis for selecting the impeller types and improving the shear rate environment in the large-scale stirred tank.

关键词： Particle image velocimetry Shear rate distribution Constant power consumption per unit volume computational fluid dynamics Scale-up

Investigation on the Natural Modes of A Semi-Closed Floating Tank

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中国海洋工程:英文版 2023年第4期37卷 580-587页

作者： WANG Guo KONG Yao-hua GE Jun-bo MA Yu-xiang SUN Lei State Key Laboratory of Ocean Engineering Shanghai Jiao Tong UniversityShanghai 200240China Marine Design and Research Institute of China Shanghai 200011China State Key Laboratory of Coastal and Offshore Engineering Dalian University of TechnologyDalian 116024China

Vessels with semi-closed tanks(i.e.,well docks)are widely applied in the military operation and maritime engineer-ing.The water is bound by the semi-closed floating tank and forced by both the incident waves and ship’s motions.The free surface oscillations inside the flooded well dock is thus distinctive and very complicated.So far,the natural modes of semi-closed floating tanks have not yet been studied.This paper investigates the characteristics of natural modes of a floating semi-closed tank by combining a mode-resolving model based on mild-slope equations and a hydrodynamic model based on computational fluid dynamics.Results show that the first three natural periods(i.e.,74,23.6,and 14 s)of the tank fall into the band of swell and infragravity waves and they could be triggered under certain circumstance.Multi-period free surface oscillations are observed inside the tank,including the longest natural period(i.e.,74 s),though the incident waves are monochromatic.A possible generation mechanism for the long-period mode is explained on the basis of liquid sloshing and harbor oscillations.Moreover,a long-period component with a period close to the natural mode of well dock is observed in the ship motions,which is generated by the interaction between the waves and ship.

关键词： floating semi-closed tank water free surface oscillations natural period natural mode mild-slope equa-tions computational fluid dynamics

Performance of large-diameter pneumatic down-the-hole (DTH) hammers: A focus on influences of the hammer structure

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Petroleum Science 2023年第4期20卷 2399-2412页

作者： Pin-Lu Cao Hong-Yu Cao Jin-E Cao Cheng-Da Wen Bao-Yi Chen Shan-Shan Yao College of Construction Engineering Jilin UniversityNo.938 Ximinzhu StrChangchunJilin130061China

Pneumatic down-the-hole (DTH) hammer has been extensively used in air drillings through hard and ultra-hard geological formations. Numerical modeling can offer close observation on the working behaviors by visualizing internal pressure status as well as provide reliable performance predictions for large-diameter DTH hammers to which conventional empirical and experimental approaches cannot be applied. In this study, CFD simulations coupled with dynamic meshing are utilized to simulate the air flow and piston movement inside the large-diameter DTH hammers. The numerical modeling scheme is verified against a theoretical model published in literature. Effects of structural parameters on hammer performance, including piston mass, piston upper-end diameter, piston groove diameter, and lengths of intake and exhaust stroke in both front and rear chambers, are analyzed in detail by virtue of sets of numerical simulations. The simulations suggest that changing the intake stroke of front chamber has a negligible influence on hammer performance while increasing the piston groove would lower all the four indicators of hammer performance, including impact energy, impact frequency, maximum stroke, and air consumption rate. Changing the other structural parameters demonstrates mixed effects on the performance indicators. Based on the numerical simulations, a large GQ-400 DTH hammer has been designed for reduced air consumption rate and tested in a field drilling practice. The air drilling test with the designed hammer provided a penetration rate 1.7 times faster than that of conventional mud drilling.

关键词： Pneumatic down-the-hole(DTH)hammer computational fluid dynamics Dynamic mesh Gas turbulent flow Piston impact performance

Structure optimization of the organ-pipe cavitating nozzle and its erosion ability test on hydrate-bearing sediments

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Petroleum Science 2023年第2期20卷 1104-1118页

作者： Xiao-Ya Wu Yi-Qun Zhang Zhen-Qiang Xu Shuai Zhao Gen-Sheng Li Shou-Ceng Tian Ya-Wen Tan Ke-Wen Peng College of Petroleum Engineering China University of Petroleum-BeijingBeijing102249China College of Safety and Ocean Engineering China University of Petroleum-BeijingBeijing102249China State Key Laboratory of Natural Gas Hydrate China University of Petroleum-BeijingBeijing102249China National Engineering Research Center of Gas Hydrate Exploration and Development Guangzhou Marine Geological SurveyGuangzhou510075GuangdongChina Guangdong Provincial Key Laboratory of Distributed Energy Systems Dongguan University of TechnologyDongguan523808GuangdongChina

Cavitating jet is a promising drilling rate improvement technology in both the marine natural gas hydrate (NGH) fluidization exploitation method and the integrated radial jet drilling and completion method. In present study, we aim to improve the efficiency of jet erosion and extracting NGH. With a computational fluid dynamics (CFD) method, the pressure, velocity and cavitation field characteristics of organ-pipe cavitating jet (OPCJ) are analysed. The divergent angle, throat length, and divergent length of OPCJ nozzle are preferred to obtain stronger jet cavitation erosion effect. Laboratory experiments of gas hydrate-bearing sediments (GHBS) erosion by OPCJ and conical jet (CJ) are conducted to compare and validate the jet erosion performance. The impinging models of OPCJ and CJ are constructed to study the impact characteristics. Results show that the preferred values of divergent angle, throat length, and divergent length are 15°, 1d, and 3d, respectively, in present simulation conditions. For GHBS, the OPCJ possesses the advantages of high efficiency and low energy consumption. Moreover, the OPCJ has higher penetration efficiency, while showing equivalent penetration ability compared to CJ. During the impinging process, the OPCJ can induce stronger impact pressure and turbulence effect, and also shows stronger chambering effect and bottom cleaning ability compared to CJ. This study presents the erosion performance of OPCJ and CJ on GHBS, and provides preliminary insights on the potential field applications in NGH exploitation.

关键词： Natural gas hydrate Cavitating jet Structure optimization computational fluid dynamics Experimental study