Table of Content

25 September 2019, Volume 47 Issue 9

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Power & Electrical Engineering

Effect of Two Electrodes on Flow Boiling Heat Transfer of R141b in Microchannels



LUO Xiaoping ZHANG Chaoyong YU Jia GUO Feng

2019, 47(9):  1-8.  doi:10.12141/j.issn.1000-565X.190202

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Two different electrode arrangements were designed to introduce the electric field into microchannels to investigate the flow boiling heat transfer characteristics of microchannels under the effect of electric field． Refrige- rant R141b was taken as the working fluid to research the influence of electric field on the flow boiling heat transfer in microchannels with designed capacity of system pressure at 140 kPa and inlet temperature at 305.65 K． The experi- mental results indicate that the electric field can enhance heat transfer of microchannels and the boiling curve of needle electrode is obviously shifted to the left． Unlike needle electrode，the boiling curve of wire electrode over- laps with the 0V and 250V and the other boiling curves are obviously shifted to the left，which manifests that the ef- fective voltage of wire electrode for strengthening is higher than that of the needle electrode． The saturated boiling heat transfer coefficient of two electrode arrangements increases first and then decreases with the increase of heat flux，and increases with the increase of mass flow rate． Compared to the electrical field-free，the saturated boiling heat transfer coefficient was increased by 39%，62%，77% respectively under three kinds of needle electrode of 250，550，850 V，and by 0%，50%，82% respectively under three kinds of wire electrode． At low voltage，the enhanced heat transfer factor of needle electrode is greater than that of the wire electrode，and the opposite is true for high voltage． Under the experimental condition，the maximum heat transfer enhancement factor of needle electrode is 1. 77，and that of the wire electrode is 1. 82．

Analytical Solution of Steady-State Temperature Field in the Plane Double Connected Domain



LU Aizhong LI Zhiyu

2019, 47(9):  9-17.  doi:10.12141/j.issn.1000-565X.180465

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At present，the analytical solution for the steady-state temperature field of the plane double connected domain mainly includes the separation variable method，the virtual heat source method，the integral transformation method and the Green's function method． These methods are only applicable to the cases with simple geometric shapes and unobstructed boundary conditions． By means of the mapping function，this study used complex variable function method to map the double connected domain with arbitrary shape in the physical plane onto an axisymme- tric circular ring in the image plane，and then transformed the partial differential equations into ordinary differential equations． By the Dirichlet boundary condition in heat transfer，the steady-state temperature field of the axisym- metric circular ring can be obtained in the image plane． Then，returning the result to the physical plane by the mapping function，the steady-state temperature field of the double connected domain in the physical plane could be obtained． For the problems of the double connected domain with known the mapping function，such as the eccen- tric circular ring and a semi-infinite domain containing a circular hole，the proposed method provided an analytical solution of the steady-state temperature field． For the problem of the general double connected domain，this study gives the method of solving the mapping function through optimization techniques，and obtains the analytical solu- tion of the steady-state temperature field of the complex double connected domain．

Friction Factor Characteristics of Rectangular Microchannels in Hydrodynamic Entrance Region



DUAN Zhipeng NING Xiaoru SU Liangbin MA Hao

2019, 47(9):  18-23.  doi:10.12141/j.issn.1000-565X.180615

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The friction factor characteristics of rectangular microchannels with aspect ratio ε from 0. 1 to 1. 0 in hy- drodynamic entrance region were investigated by using the Fluent software． The results reveal that the aspect ratio ε and Reynolds number Re have effects on the product (f_app Re) of the apparent friction factor and Reynolds number． The f_app Re of rectangular microchannels decreases as the aspect ratio ε increases，and different effects are presented in the different range of Re． The f_app Re decreases with the increase of Re when Re is less than 300; while the f_app Re varies slightly when Re is more than 300． When the flow is fully developed，the f_app Re remains unchanged and be- comes nearly independent of Reynolds number． The effects of ε and Re on the hydrodynamic entrance length is also studied． It is found that when Re is less than 20，the dimensionless entrance length gradually decreases with the in- crease of the aspect ratio ε． When Re is more than 20，the dimensionless entrance length first increases and then decreases with the increase of the aspect ratio ε，and reaches the peak value as the aspect ratio is between 0. 3 to 0. 4． Based on the obtained results，a new hydrodynamic entrance length correlation for laminar flow was proposed， which may provide guidance for the design and optimization of microchannels．

Operational Control Strategy of Non-uniform Load Matching for Multiple Chillers



LIU Xuefeng ZHENG Yulan WANG Jiaxu LU Zhitao

2019, 47(9):  24-32,39.  doi:10.12141/j.issn.1000-565X.190031

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Taking the chiller group with non-uniform cooling capacity as the research object，considering the self- balancing characteristics of cooling capacity，the thermal model of parallel operation of multiple chillers was con- structed，and the parallel operation characteristics of non-uniform load matching chillers under variable load were studied． The optimal control strategy of chiller of the energy efficiency benchmark was compared with the uniform load matching chiller． The applicability of the non-uniform load matching control strategy under the chilled water effluent temperature was discussed． The results show that under the condition of self-balance of cooling capacity， there are energy efficiency benchmarks when multiple chillers are operated in parallel，and the chiller group can achieve the maximum energy efficiency ratio according to the control strategy corresponding to the energy efficiency benchmark． When the load rate of the air conditioning system in this example varies from 14% to 39% and from 43% to 100%，the average energy efficiency ratio of the chiller group is EER≥ 5，and the maximum EER is 5. 43; under the operating conditions of variable chilled water supply temperature，the control strategy of chiller does not change with the effluent temperature of chilled water，and has good applicability; when the chiller selec- tion and matching are carried out in the actual project，the non-uniform load matching method with a small number of chillers operating in parallel to achieve higher overall operating performance should be prioritized．

Subsection Control of Wave Power Generation System Based on Trajectory Planning



YANG Jinming HUANG Xiuxiu CHEN Yuanrui XIE Zekun

2019, 47(9):  33-39.  doi:10.12141/j.issn.1000-565X.180539

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Subsection control strategy of power generation at high-speed and energy storage at low-speed was used to solve the low efficiency problem of direct-drive wave power generation system based on the fully enclosed oscilla- ting floating wave power generation system． The control of integrated maximum power acquisition was studied com- bining with passivity-based control． In order to avoid the fluctuation and shock phenomena in the process of sub- section control，the energy trajectory of the switching process was planned by using the differential smoothing theo- ry． The simulation results show that the application of subsection control strategy and the differential smoothing theory can not only improve the power generation efficiency but also avoid shock impact．

Modeling and Simulation of Fine Particle Composite Coagulation Based on Orthogonal Design



LIU Dingping HUANG Junqin QIN Fangbo LUO Weile

2019, 47(9):  40-46,97.  doi:10.12141/j.issn.1000-565X.190067

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In order to study the sensitivity of factors affecting the coagulation efficiency of fine particles，a compo- site coagulation model suitable for different coagulation approaches was established，coupling the particle goup po- pulation balance model with the Euler's multiphase flow model and using the user-defined function to simultaneously introduce the Brownian-turbulent-acoustic composite coagulation kernel function and the condensation growth rate function． The numerical simulation of fine particle composite coagulation process was performed by using orthogonal design，and the primary and secondary relations of the effect of initial steam supersaturation，residence time， sound pressure level and sound frequency on the coagulation process were analyzed based on the simulation results． The simulation results show that the model can effectively characterize the coagulation efficiency of PM_2.5 particles． Through orthogonal simulation tests of coagulation efficiency of PM₁₀ and PM_2.5 ，it is further concluded that the in- fluence degree of each parameter under composite coagulation is: sound pressure level ＞ residence time ＞ initial steam saturation ＞ sound frequency． The increase of sound pressure level，residence time and initial steam satu- ration is conducive to the improvement of coagulation efficiency，while there is an optimal value of sound frequency to maximize the coagulation efficiency，and the optimal frequency of PM_2.5 coagulation efficiency is higher than that of PM₁₀ ． The establishment of the model is significant to the research on the influence degree of correlation parame- ters for fine particle composite coagulation．

Traffic & Transportation Engineering

Incorporating Heterogeneity into Travelers' High-Speed Rail Station Arrival Mode Choice



LIU Jianrong LIU Zhiwei REN Qian

2019, 47(9):  47-52.  doi:10.12141/j.issn.1000-565X.180419

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Utilities of travelers' arrival modes to a hub station are important factors that affect travelers' mode choice． There is heterogeneity among travelers' preference of mode choice，and the traditional discrete choice mode can't explain the heterogeneity clearly． This study incorporated the heterogeneity into travelers' mode choice to the high-speed railway station with the latent class conditional Logit model． The latent class conditional Logit model produced segment-specific parameter estimates to capture heterogeneous preferences for choice alternatives and identified travelers' profiles for each segment． The results show that the sample population can be divided into three subgroups，and the parameters of in-vehicle time，walking time and price varies in each subgroup． Further- more，the car-ownership，monthly income and latent variables (flexibility，comfort，reliability) have significant influences on the category classification of the sample population．

Analysis of Commuting Mode Based on Behavior Dynamics of Time Characteristics



YAO Shushen WENG Xiaoxiong LI Feiyu

2019, 47(9):  53-60.  doi:10.12141/j.issn.1000-565X.180647

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Public transportation is an effective measure to solve urban traffic congestion problems． As a major par- ticipant in urban public transportation，commuting groups and their behavioral patterns have long been the focus of academic research． The study constructed the passenger bus travel time interval distribution with behavior dynamics method based on the whole sample travel data． It demonstrates the universality of“power law representation”of human behavior from the group level． But at the same time，the phenomenon of“power law dissipation”has been observed in some individual samples． In-depth study finds that the individuals deviating from power law fitting characteristics have more regular travel rules generally． Further，the clustering methods of commuter passengers was proposed based on curve fitting parameters and travel interval spectral function． The methods can solve the subdivision problem of commuter passengers intuitively and effectively． The case of Zhuhai shows that the research has a strong practical value for in-depth study of urban public transport travel rules．

Bus Travel Choice Reversals Based on the Equate-to-Differentiate Theory



ZHANG Nian LUO Xia ZHANG Ke

2019, 47(9):  61-67.  doi:10.12141/j.issn.1000-565X.190010

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Choice reversal is a paradox phenomenon in traffic behavior，and it can not be well explained through error cautious control． From the perspective of decision psychology，the judgment dimension system of option at- tributes，and carries out three groups of psychological experiments in different bus travel decision situation was es- tablished based on the equate-to-differentiate theory． Through the matching task，it was confirmed that choice can be explained under the equate-to-differentiate interpretation． Through the retest reliability analysis for choice con- sistency，it was proved that the judgment for dimension is variable． Through the retest reliability analysis for choice and matching consistency，it was proved that choice reversals are caused by the change of the dimension judgment in matching task． The equate-to-differentiate interpretation shows good consistency in the three groups of experiments． The judgment dimension system can predict and explain the travel choice reversal． That is，the in- explicable paradox occurs when diverse equate-to-differentiate strategy is used．

Electric Bus Area Driving Plan Preparation Considering Charging Constraints



YAO Enjian LU Muyang LIU Yuhuan YUAN Ling

2019, 47(9):  68-73.  doi:10.12141/j.issn.1000-565X.180553

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Electric vehicles are widely used for their excellent characteristics such as low pollution and high com- fort with the increasing environmental pollution of fuel vehicles and the increasing emphasis on passenger comfort by public transportation． However，due to the limitation of cruising range and charging demand，electric vehicles driving plan is rather complicated． Under the premise of multi-station regional scheduling mode，this study fully considered the occurrence and execution of charging tasks，and the optimization of total fixed cost and total opera- ting cost including electric bus and its supporting facilities． The regional driving plan was modeled，and a compound solving algorithm was designed based on genetic algorithm and greedy algorithm to solve the model． Finally，the ope- ration plan model was verified by taking some line operations in Daxing District of Beijing as an example，and com- pared with the traditional bus planning method． The results show that the total operating cost is reduced by 18. 20%．

Target Ratio Decision and Control of CVT Based on Power Demand



LEI Yulong HU Jianlong FU Yao ZHANG Ying WANG Linbo

2019, 47(9):  74-82.  doi:10.12141/j.issn.1000-565X.180484

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The speed ratio control of CVT is the key technology to optimal fuel efficiency of the power system． Ai- ming at the problem of slow response and difficulty of real-time precise control for traditional PID ratio control， CVT target speed ratio decision method based on Markov model for predicting power demand was proposed． K- means algorithm of cluster analysis was used to solve the problem． The boundary value of the different moments of the moment demand value was used to divide the state space of the dynamic demand Markov model，and the de- mand torque law obtained by the NEDC cycle condition was calculated． The speed ratio control method of the pre- control plus integral separation PID was proposed． Introducing the differential first and adding the speed ratio pre- control system to determine the target speed ratio change rate can achieve fast follow-up of the speed ratio，and at the same time weaken the speed ratio overshoot phenomenon． The main and driven wheel pressure control strategy was proposed，and the PID controller with Smith correction was adopted． This method can prevent the system from overshooting and make up for the defects of the hydraulic system． The bench test shows that this method can sup- press the overshoot phenomenon in speed ratio control and improve the speed ratio control accuracy．

Modal Analysis and Optimization of Vehicle Steering System



TANG Liang LI Yi ZHANG Zhirui CHENG Yiming SHANGGUAN Wenbin

2019, 47(9):  83-89.  doi:10.12141/j.issn.1000-565X.190063

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The idle vibration of steering wheel in the vehicle steering system is an important index to evaluate its comfort． A calculation method of steering system's natural frequency was put forward． Through sensitivity analysis， the thicknesses of five sheet metal parts at the upper and lower connections of steering system was determined as the design variables． Based on the combination of response surface model and sequential quadratic programming algo- rithm，the modal optimization method of steering system was presented． The first-order natural frequency of the system increased by 2. 66 Hz when the mass of the steering system increased by 0. 14 kg． The steering system mo- dal analysis and the proposed optimization method can provide certain guidance for steering system design．

Deep-Learning-Based Lane-Keeping Control Framework: From Virtuality to Reality



YANG Shun WU Jian JIANG Yuande WANG Guojun LIU Haizhen

2019, 47(9):  90-97.  doi:10.12141/j.issn.1000-565X.180221

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Deep-learning-based approaches have been widely used for training controllers for autonomous vehicles due to their powerful ability to approximate nonlinear functions or policies． However，the training process usually requires large amount of labeled real-world driving dataset，and the data collection and labeling process is always time and money-consuming． Corner-case data collecting is difficult for human，which may lead to poor generaliza- tion ability of the training model and hamper the promotion of the deep learning controller performance． Thus a framework was proposed to train an end-to-end convolutional neural network (CNN) controller in virtual game en- gine TORCS and generalized the trained controller into reality． To narrow the gap between virtual and real environ- ment，semantic segmentation was used as medium． The training dataset from game engine and the testing data from reality are all translated into semantic segmentation style for both training and validation． Validation result shows that the trained lane keeping controller can be deployed to solve the real-world driving task and get a good performance． Compared with human driver operation，the changing trends of the fine-tuned CNN controllers' out- put is consistent with human driver，the maximum MAE and RMSE are 1. 6939°and 2. 8850°，and the average MAPEs are all under 5%．

Mechanical Performance Analysis of One Tube Composite Bonding-Type Anchorage of CFRP Tendons



JIA Lijun ZHANG Chuan CONG Xiao

2019, 47(9):  98-106.  doi:10.12141/j.issn.1000-565X.180642

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Mechanical performance，transversal stress and displacement of one tube composite bonding-type an- chorage was analyzed by using finite element method and introducing the concept of anchorage efficiency． The aim is to investigate the mechanical performance of bonding-type anchorage as well as the parameters' effects on the an- chorage efficiency，to find out the optimized parameters of anchors，and to solve the problems of anchorages and promote the applications of CFRP (Carbon Fiber Reinforced Polymer) in large-span bridges． Furthermore，based on the concept of anchorage efficiency and equivalent stiffness，the effects of anchors' length，elastic modulus of bond medium，length of straight tube，inner angle of barrel，thickness of tube as well as diameters of CFRP ten- dons on the anchorage efficiency were studied by changing the parameters of models． Results show that the anchors' length is suggested to be 12 to 16 times of the diameters of CFRP tendons; the elastic modulus of bond medium is suggested to be 1. 5 GPa to 3. 0 GPa; the length of straight tube is suggested to be 1/6 to 1/2 of anchors' length; the inner angle of barrel is suggested to be 4° to 5°; the thickness of medium is suggested to be 0. 3 to 0. 5 times of diameters of CFRP tendons; the diameters of CFRP tendons is suggested to be less than 90 mm． Under the sug- gested parameters，the anchorage efficiency can reach 90% ～95% or even more． Hence，it does help to promote the anchorage efficiency and equivalent stiffness by optimizing the parameters of anchors．

Environmental Science & Technology

Characteristics of Diversity and Community Structure of cDCE Mineralized Aerobic Bacteria



LYU Cong JU Lunan LIU Jialu REN Hang ZHAO Zhiquan FANG Chen LI Chenyang DU Jun

2019, 47(9):  107-112,138.  doi:10.12141/j.issn.1000-565X.180483

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Organic chlorine solvent，as an important chemical raw material，may lead to serious pollution in the process of use． At present，the concentration of cis 1，2-dichloroethylene (cDCE) has been detected in ground- water of many organic chlorine contaminated sites，and its toxicity is much greater than that of trichloroethylene and tetrachloroethylene． In view of the problem of microbial aerobic mineralization of cDCE in groundwater contamina- ted by organochlorine，organic chlorine contaminated groundwater was taken as a source of bacteria in a certain area． After 338 days' enrichment and domestication，the cDCE mineralized aerobic bacteria was finally cultured． The cultured cDCE aerobic mineralized mixed bacteria showed better ability to metabolize cDCE． At the initial concen- tration of cDCE concentration of 1 mg/L，the degradation rate was 38. 1% after 16 days． In order to enrich its bio- logical information，16S rRNA high-throughput metagenomic sequencing technology was used to analyze mixed bac- teria in different periods during domestication，and molecular biological information of mixed bacteria was ob- tained． The samples in different culture stages have certain continuity; their diversity decreases first and then in- crease with the culture of microorganisms． At the same time，the community structure of microorganisms at diffe- rent stages was obtained． Combined with other biological information and the ability of microorganisms to metabo- lize cDCE during culture，it is speculated that cDCE mineralized aerobic bacteria belongs to the genus Delftia．

Isolation and Identification of Heterotrophic Nitrification Bacterium and Nitrification Performance Analysis of Mixed Culture of Multi-strains



MENG Hailin LIU Furong HE Jingyu ZHANG Wenyan ZHANG Honggang CUI Jinming

2019, 47(9):  113-120.  doi:10.12141/j.issn.1000-565X.180318

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Heterotrophic nitrifier with high ammonium and nitrite nitrogen removal ability was isolated from the aquaculture pond，and the nitrification performance of mixed culture of multi-strains was studied． The strains were isolated from sediment，waters and intestinal tract of fish samples in the high density aquaculture ponds by enriching with NH ₄ Cl and NaNO ₂ as a sole nitrogen source respectively and identified by sequence analysis of 16S rDNA． Ammonium and nitrite nitrogen removal ability was investigated under aerobic conditions． The selected strains were quantitatively mixed to evaluate the ammonium removal efficiency under different culture conditions such as carbon source，C/N ratio，initial pH，and NaCl concentration． The nitrifying characteristics were investigated of single， pairwise，three-member microbial community under the optimal conditions． Eight heterotrophic nitrobacteria were isolated and three strains showed the higher ability of removing ammonium and nitrite nitrogen belonged to Bacillus megaterium (W3-1)，B． subtilis (YZN-2) and Lactobacterium plantarum subsp． (HT1-1)，respectively． The NH ₄ ⁺ -N removal efficiency was 71. 2%，61. 3% and 60. 7%，while NO ₂ ^－ -N removal efficiency was 38. 7%， 35. 6% and 37. 6%，respectively． After the optimization of mixed culture，the results show that under the condi- tions of sodium citrate as carbon source，C/N for 20，NaCl concentration for 5 g/L and pH 6，the mean ammoni- um removal rate is 2. 05 mg/ (L·h ^－1 ) in 24 hours． In the community of W3-1 + HT1-1 and W3-1 + YZN-2 + HT1-1，the ammonium removal rate is promoted by HT1-1 at the early stage，e． g． the average ammonium re- moval rate of W3-1 alone is 1. 61 mg/ (L·h ^－1 ) during first 9 h，while the rate of W3-1 + HT1-1 and W3-1 + HT1-1 + YZN-2 raise to 2. 51 mg/ (L·h ^－1 )，and 2. 49 mg/ (L·h ^－1 )，respectively． The above results in- dicate that the strains of W3-1，YZN-2 and HT1-1 show higher heterotrophic nitrification ability than others． The ammonium removal rate of B． subtilis is improved by combination with L． plantarum． The research provides necessary theoretical reference for the fast start of nitrification system in the sewage treatment process and the deve- lopment of nitrifier agents．

Chemistry & Chemical Engineering

Research Progress on Cellulase Biodegradation Mechanism



ZHANG Jun XU Chao ZHANG Yu LIANG Cuiyi XU Jingliang

2019, 47(9):  121-130.  doi:10.12141/j.issn.1000-565X.180560

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Cellulase plays an important role in the biorefinery process，so it is necessary to deeply understand the mechanism of enzymatic hydrolysis． Cellulose as polymer compound formed by the polymerization of D-glucose， which is an important component of biomass，and the degradation of cellulose is the most significant step in the de- structing process of lignocellulose． Due to its stable molecular structure，only through synergistic action of various domains and components of the cellulase can it be biodegraded into available saccharides． The recent research on the mechanism of cellulase degradation at home and abroad was reviewed． This review firstly explored the interac- tion between structure and function to reveal the relationship of between them and analyzed the molecular mecha- nism of biocatalyst，which provides theoretical basis for optimizing cellulase structure to improve catalytic ability． Secondly，the characteristics and molecular structure of cellulase degradation mechanism were discussed，and the important effect of its enzymatic synergy and environment on the enzyme activity was also investigated in order to provide references for the optimization design of enzymatic hydrolysis system． Finally，by combining the mecha- nism of cellulase biodegradation，the effective ways to reduce enzyme costs was summarized．

Highly Accurate Prediction Models for Thermophysical Properties of PCMs



LI Yajun ZHANG Jinwen

2019, 47(9):  131-138.  doi:10.12141/j.issn.1000-565X.180612

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Aiming at the limitations of experimental study on thermophysical properties of cryogenic PCMs，such as long duration，big deviation and harsh cold condition test，a highly accurate method to predict solid-liquid equi- librium (SLE) of PCMs，where SRK-UNIFAC model is used in the fugacity of PCMs in liquid phase and method of referenced state by hypothetic path is used in solid phase，was proposed． Based on the improved method，the thermophysical properties of composite cryogenic PCMs including eutectic composition，eutectic temperature and eutectic enthalpy were accurately predicted with a minor deviation． Furthermore，taking the LNG air separation unit as an example，the established simulating method with high accuracy to predict PCMs' thermophysical proper- ties was adopted for material selection and adaptive application for cryogenic energy storage unit in this project with high efficiency．

3D Simulation of Explosion Characteristics of Pentane in Class A Warehouse and Explosion-Proof Strategies



ZHANG Qiang CHEN Guohua XUE Yongzhi HU Sheng

2019, 47(9):  139-146.  doi:10.12141/j.issn.1000-565X.180582

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Software FLACS was used for 3D modeling and 3D dynamic simulation of effects of different ignition po- sitions，different equivalence ratio of fuel-air and the number of stacking layers on explosion overpressure，in order to study the explosion characteristics of pentane vapor cloud in a class A warehouse． And the worst explosion sce- nario was determined． Taking the explosion of pentane vapor cloud as an example，the simulation results show that when the ignition position is at the edge of the pentane vapor cloud and closed to the firewall，large explosion over- pressure is easily produced; the maximum explosion overpressure increases first and then decreases with increase of the equivalent ratio of pentane-air，and decreases with the decrease of the number of stacking layer; under the worst explosion scenario (ignition position is in the middle of the firewall，number of stacking layer is 3 and equiva- lent ratio of pentane-air is 1. 35)，the maximum explosion overpressure is 727 kPa． The research results can pro- vide reference for explosion-proof design of class A warehouses for hazardous chemicals．