Journal of South China University of Technology(Natural Science Edition)

Effect of Surfactant on Flow Boiling Heat Transfer of Al2O3/R141b in Microchannels

2019, 47(5): 1-8,155. doi:10.12141/j.issn.1000-565X.180391

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In order to investigate the effect of surfactants on the flow boiling heat transfer of nanofluids refrigerant Al2O3/R141b in microchannels, two-step process was used to prepare 0.2wt%SDBS, 0.3wt%SDBS, 0.3wt%CTAB, 0.4wt%CTAB, 0.1wt%Span80, 0.2wt%Span80 modified nano-refrigerant and 0.1wt%Al2O3/R141b pure nano- refrigerant. The flow boiling and heat transfer experiment of surfactant modified nanometer refrigerant was carried out in a rectangular microchannels with a height of 2.0mm and a width of 1.0mm respectively，and the design system pressure was 170kPa, the heat flux density was 9.4 kW/m2 to 33.5 kW/m2, and the mass flow rate was 219.9 kg/(m2?s)~439.8 kg/(m2?s). The results showed that the surfactant has significant effect on the flow boiling heat transfer coefficient of nano-refrigerant, the average heat transfer coefficient of the nano-refrigerant saturated boiling zone increased by 27.7%, 17.9%, 13.8%, 8.9%, 7.9%, and 5.3% when the surfactant was 0.2wt%SDBS, 0.3wt%SDBS, 0.3wt%CTAB, 0.4wt% CTAB, 0.1wt%Span80 and 0.2wt%Span80, respectively, compared with the pure nano-refrigerant. The smaller the agglomerated particle size of the surfactant-modified nano-refrigerant, the larger the heat transfer coefficient. The surface activity enhancement factor (SEF) increased with the increase of the mass flow rate, and the SEF decreased with the increase of the heat flux density at the same mass flow rate. The anionic surfactant SDBS has the best effect on the fluid boiling heat transfer of nanofluids, the cationic surfactant CTAB is the second, and the nonionic surfactant Span80 is the worst.

Influence of Ions Distribution of Anion-Exchange Membranes on Diffusion Dialysis of Acid Recovery

LI Xiuhua YUE Xi ZHONG Shixi ZHOU Yang LIAO Shijun

2019, 47(5): 9-17. doi:10.12141/j.issn.1000-565X.180159

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In order to reveal the effects of ionic group structure and ions disctribution on the diffusion dialysis of anion exchange membranes ( AEMs) ，three kinds of side-chain ionic poly( arylene ether) AEMs and a main-chain ionic poly( arylene ether) AEM were synthesized． Then，the four kinds of AEMs were characterized and evaluated in terms of structure，basic performances，acid stability，mechanical properties and diffusion dialysis performance． The results indicate that the symmetric side-chain ionic AEMs have better permeability selectivity and the main-chain ionic AEM has the best permeability selectivity owing to its symmetric ionic structure and dense aggregate structure，and that the basic performances，acid stability and mechanical properties of the AEMs all make clear that the prepared AEMs satisfy the basic acquirements of an diffusion dialysis process． Moreover，the experimental results of diffusion dialysis in simulated waste acid indicate that the prepared AEMs have better diffusion dialysis performances than those of the commerical TWDDA1，especially the main-chain ionic AEM，which wins the competition of diffusion dialysis at room temperature with an excellent proton diffusion coefficient of 0. 025 m /h and a top separation factor of 42. 49． All these mean that QMPAES has a great potential for acid recovery via diffusion dialysis．

Dissolution Mechanism of Wheat Straw Alkaline Lignin in Alkaline Ionic Liquid ［Bmim］［OH］

HOU Yi ZHANG Xiao LIU Chao LI Youming

2019, 47(5): 18-24,31. doi:10.12141/j.issn.1000-565X.180253

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This paper deals with the structure variation of wheat straw alkali lignin in alkaline ionic liquid ［Bmim］［OH］and the dissolution mechanism of alkali lignin． The dissolution was assisted by microwave heating with a microwave power of 500 W，a temperature of 90 ℃，a reaction period of 30 min and a solid-to-liquid ratio of 1∶10． By using ［Bmim］［OH］ionic liquid as a solvent，the lignin dissolution process was characterized and analyzed by means of FT-IR，GPC，elemental analysis，2D HSQC NMR and Py-GC-MS． The results indicate that，during the dissolution of alkali lignin in ionic liquid ［Bmim］［OH］，the aromatic rings remains stable and there mainly occurs the substitution of the side chain or the removal of oxygen-containing groups; and that，after the dissolution，the relative molecular mass of the regenerated lignin slightly decreases，the molecular mass distribution become more uniform and the degree of unsaturation increases due to the dehydration reaction during the dissolution processes． Moreover，2D HSQC NMR and Py-GC-MS results prove that there mainly happens the cleavage of β-O-4' aryl ether linkages during the dissolution of lignin in strongly basic ionic liquid system，followed by β-β and β-5 structures，and the S /G ratio remarkably decreases． This research provides basic data and an approach to the development of relevant theories and the application of high-value alkali lignin

Application of Scaled Particle Theory to Extraction of 2，3-Butanediol Model Solutions

YI Conghua SONG Wenli

2019, 47(5): 25-31. doi:10.12141/j.issn.1000-565X.180580

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In order to provide a theoretical guidance for the selection of salting-out agents and extraction agents， the ionic salvation free energies of eleven kinds of salts and three kinds of solvents in 10% 2，3-butanediol model fermentation solutions were calculated based on the scaled particle theory，with the corresponding extraction effects being ranked according to the experimental extraction results obtained at 37 ℃ ． It is found that，in the several parts consisting of the standard molar solvation free energy，the electrostatic free energy between the salt and the solvent，whose larger absolute value means better salt extraction effect，is the key factor affecting the extraction; and that，with the increase of absolute value of the standard molar solvation free energy，the mass fraction of 2，3- butanediol increases linearly，while that of water decreases linearly

Depolymerization Property of Alkali Lignin in Solvent/Water System

ZHAO Yuanyuan WU Shubin LIAO Yanfen

2019, 47(5): 32-38. doi:10.12141/j.issn.1000-565X.180521

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In order to investigate the depolymerization characteristics of alkali lignin in solvent /water mixture systems，four systems，namely ethanol /water，ethyl acetate /water，ethylene glycol /water and pure water，were selected to perform experiments． The results show that ( 1) ethanol /water mixed solvent medium helps to obtain the highest yield of liquid products and total phenolic compounds; ( 2) under the optimal reaction condition ( a temperature of 300 ℃，a reaction time of 30 min，a rotational speed of 500 r/min，a formic acid dosage of nickel of 10% and an ethanol-to-water volume ratio of 40∶60) ，the yields of liquid products and total phenolic compounds are 73. 88% and 14. 45% ，respectively; and ( 3) after the flashing at 200 ℃ and the pyrolysis at 500 ℃ of the liquid products，the phenolic compounds derived from lignin's basic structural unit are the most abundant，thus greatly increasing the yield of monophenol． Moreover，the methyl aryl ether bond of the distillation residue may break down during the pyrolysis process，which leads to the formation of a certain amount of catechol． All these above-mentioned statements provide guidelines for the quality improvement and utilization of liquid products．

Flame-Retarded Nylon 6 by the Synergy of Melamine Stannous Phosphate Glass with Aluminum Diethylphosphinate

LIU Shumei XIA Wei ZHU Ruizhe CAI Jianan ZHAO Jianqing

2019, 47(5): 39-47. doi:10.12141/j.issn.1000-565X.180470

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Stannous phosphate glass was prepared by melting stannous oxide and phosphorus pentoxide at a molar ratio of 50∶50 at 500 ℃，which was then combined with melamine by ionic bond to form melamine stannous phosphate glass ( MEPglass) ． Finally，MEPglass and aluminum diethylphosphinate ( AlPi) were employed to obtain halogen-free flame-retardancy of PA6． It is found that 0. 5% MEPglass and 9% AlPi can induce PA6 to reach UL94 V-0 @ 3. 2 mm rating，with a total relative addition reduction of 26. 9% ，as compared with the addition ( 13% ) of single AlPi，while the tensile strength improves by 8. 5% and the melt flow rate increases by 13. 3% ． Moreover，the results obtained from the cone calorimeter，thermogravimetry-infrared spectroscopy and thermogravimetric analysis of the samples，and scanning electron microscopy and X-ray energy spectrum analysis of carbon residue indicate that there is strong flame-retardant synergy of MEPglass and AlPi on PA6 in both the gas phase and the condensed phase．

Elastic Property Prediction of Materials Based on Machine Learning and Feature Selection

2019, 47(5): 48-55. doi:10.12141/j.issn.1000-565X.180214

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This paper deals with the elastic property prediction of inorganic materials by using three feature selection methods ( Filter，RFE and LASSO) and three machine learning algorithms ( linear regression，ridge regression and support vector regression) ． In the investigation，first，the best feature subset is selected to predict the elastic properties of inorganic compounds from a large number of multi-scale feature sets． Next，the most effective model that combines both feature selection and machine learning is identified for predicting the elastic properties of materials． Then，the performances of different combinations of feature selection methods and machine learning models are compared by anlyzing the feature subset obtained via different feature selection methods． Experimental results indicate that ( 1) Filter + SVR method helps to achieve the best prediction performance; ( 2) the machine learning model has greater influence on the prediction results than the feature selection method; and ( 3) the feature subset selected by the feature selection method mainly includes the material characteristics such as melting point，crystal structure and Mendeleev number． This research provides a way to finding predictive descriptors for elastic property of inorganic compounds and developing more effective prediction methods．

Hysteresis Torque Rolling Resistance Model Based on Discrete Element for Plastic Materials

WANG Anlin YU Yongqiang LI Xiaotian WANG Chuxin

2019, 47(5): 56-62，72. doi:10.12141/j.issn.1000-565X.180279

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As the original spring-damper rolling resistance model cannot accurately express the change of the deformation of plastic materials，this paper presents a new rolling resistance model based on discrete element for plastic materials，namely the hysteresis torque rolling resistance model． In this model，based on the elasto-plastic deformation theory of particle materials，the rolling resistance torque of the discrete element particles is described as a hysteresis term and a damping term． The hysteresis term expresses the force imbalance caused by the state that the front half of the contact portion is in the deformation process and the latter half in the recovery process，while the damping term expresses the friction on particle surface． The presented rolling contact model is then verified by a particles pile test and achieves a more accurate expression of the unbalanced plastic deformation state on both sides of the particle contact center． From the viewpoint of microscopic process of particle contact，the proposed model is more consistent with material's elastic-plastic deformation mechanism and can be widely used to simulate plastic materials

Modification of Ceramsite by FeCl3 and the Corresponding Enhancement of Heavy Metals Adsorption

YANG Yongmin QIAO Ruilong XIE Xiaogeng ZHANG Tongsheng LIU Xiaofei

2019, 47(5): 63-72. doi:10.12141/j.issn.1000-565X.180558

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In order to improve the adsorption capacity and stability of ceramsite in wastewater with high heavy-metal concentration，porous ceramsite was modified via a pretreatment in FeCl3 solution and a calcination process． Then，the surface morphology of the ceramsite and the removal rates of heavy metals affected by the number of immersion-drying cycles，FeCl3 solution concentration and calcination temperature were investigated． The maximum adsorption capacity was achieved when the ceramsite was immersed in 1. 5 mol/L FeCl3 solution for 3 immersion-drying cycles and then calcined at 650 ℃． In a high heavy-metal concentration environment，the adsorption amount of Cu2 + increases from 0. 188 to 0. 897 mg/g，and the leaching rate of Cu2 + decreases from 3. 52% to 0. 96%． Moreover，the removal rates of Pb2 + ，Cu2 + and Cd2 + by the modified ceramsite respectively achieve 15. 0%， 22. 4% and 50. 1%，which are 7. 7，8. 9 and 9. 7 times that by the original ceramsite，respectively．

Internal Micro-Deformation Analysis of Recycled Aggregate Concrete Based on CT Images

HAN Yanhua XIE Zuowei LIU Fang FU Shaojun

2019, 47(5): 73-80. doi:10.12141/j.issn.1000-565X.180599

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In order to study the internal deformation of the early-age recycled aggregate concrete in the process of uniaxial compression，recycled concrete specimens under different axial loads，which respectively possesses the recycled coarse aggregate replacement rates of 0，30% and 50%，were scanned by means of Xray industrial computed tomography ( CT) ． Then，by taking the grayscale distribution in CT images as a speckle pattern and the CT images captured before and after the loading as the carrier of deformation information of the specimens，the internal realtime displacement fields and strain fields of the recycled concrete specimens were obtained via MatchID， and the corresponding deformation contours were drawn to visually reveal the evolution of the internal micro-deformation of recycled concrete specimens in the compression process． It can be shown that there is a positive correlation between the internal deformation of the specimens and the replacement rate of recycled coarse aggregate under the same loading conditions，and that the localization deformation characteristics of specimens with the same recycled coarse aggregate replacement rate become obvious with the increase of axial load． The proposed method combining CT images and MatchID algorithm provides a new approach to exploring the micro-deformation of recycled aggregate concrete．

Failure Rate Evaluation of Tool Storage and Selection System Based on Fuzzy Evidence Theory

2019, 47(5): 81-88. doi:10.12141/j.issn.1000-565X.180401

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The tool storage and tool selection system is the weak link of a machining center． The accurate evaluation of the system's failure rate is important to the improvement of machine reliability． However，due to the lack of fault data and the high complexity of the system itself，there exists uncertainty in evaluating the failure rate of system components． In order to solve this problem，this paper comprehensively considers the multisource influencing factors causing the failure，uses the evidence theory to deal with the uncertain information effectively，combines the multisource information by means of projection weighting，and adopts the reliability fuzzy language set theory to deal with the fuzzy treatment of the influencing factors of fault rate． Then，the evaluation results of the component failure rate expressed by interval number are obtained． Finally，an example application of the tool storage and selection system of a certain machining center in China is conducted to verify the effectiveness and feasibility of the proposed method

Microstructure and Mechanical Properties of Al 7075 Alloy Prepared by Cryogenic-Temperature Extrusion Machining

YIN Xiaolong DENG Wenjun ZHANG Jiayang PI Yunyun

2019, 47(5): 89-95. doi:10.12141/j.issn.1000-565X.180396

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Large amounts of heat generate during the preparation of ultrafine grained materials，which may decrease the strength of materials． In order to solve this problem，a new method named cryogenictemperature extrusion machining ( CT-EM) was put forward． In this method，Al 7075 alloy was chosen as the workpiece material and roomtemperature extrusion machining ( RT-EM) was also conducted for a comparison in terms of chip morphology，microstructure and mechanical properties． The results indicate that ( 1) the chips prepared by CT-EM and RT-EM are continuous and segmented，respectively; ( 2) the surface of the chip obtained by CT-EM possesses fewer defects with better integrity; ( 3) the maximum hardness of CT-EM and the RT-EM samples are 190 ( HV，the same as follows) and 175，respectively，which are far greater than that of the original material ( 105) ; ( 4) after the CT-EM process，the grains are highly refined to less than 200 nm in diameter; ( 5) the grain refinement and dislocation strengthening are two main strengthening mechanisms for Al 7075 alloy; and ( 6) as CT-EM Al 7075 alloy possesses higher dislocation density，the contribution of dislocation strengthening to hardness is greater．

Reliability Modelling for Degradation Based on Type-Ⅱ Generalized Logistic Distribution and Particle Swarm Optimization

ZHANG Jinbao ZHAO Yongqiang LIU Ming KONG Lingxian

2019, 47(5): 96-102. doi:10.12141/j.issn.1000-565X.180091

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As the generalized probabilistic distribution can describe the characteristics of performance degradation data with high precision and reduce the impacts caused by the outliers and the fault selection of probabilistic distribution，the type-Ⅱ generalized logistic distribution ( Ⅱ-GLD) is applied to the degradation reliability evaluation in this paper． In the investigation，the parameters of location and scale are introduced in the modeling of time-dependent degradation data，the objective function is established according to the meansquare error ( MSE) between the quantiles of Ⅱ-GLD and the experiment data，and particle swarm optimization ( PSO) algorithm is utilized to estimate parameters simultaneously． Then，the proposed approach is applied to a practical example for the evaluation of degradation reliability，followed with a verification and comparison． The results show that the relative errors between the mean and the standard deviation are below 8%，and that the reliability evaluation results match well with the pseudolifetime data in different failure thresholds． Moreover，it is indicated that，as compared with the normal distribution and the Weibull distribution，Ⅱ-GLD can explore the tail characteristics of degradation data more effectively and represent the initial degradation of the product faithfully．

Investigation into Method of Force-Finding Analysis for Kiewitt Cable Domes

JIANG Zhengrong ZHANG Zijian SHI Kairong GU Xuejin LUO Bin

2019, 47(5): 103-109,122. doi:10.12141/j.issn.1000-565X.180420

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By taking the Kiewitt cable domes which contain multiple overall selfstress modes as the research objects，this paper deals with the improvement of ratio-updating method for forcefinding analysis of cable domes with single overall selfstress mode and proposes a new approach to forcefinding analysis of Kiewitt cable domes，with its applicability being validated by examples later． Moreover，the key members are designated and prestressed to perform an iterative computation，and，by using the mode error analysis method based on the leastsquares，a comparison of the results respectively obtained by the proposed method and the singular value decomposition method is carried out． The results show that，as compared with the singular value decomposition method，the proposed improved ratio-updating method possesses high accuracy and helps to obtain overall feasible selfstress modes with clear meaning in the mechanical concept of cables in tension and struts in compression，thus providing a new idea and solution for the prestress determination of cable domes．

Seismic Behavior of Circular Steel Tube-Confined H-Steel Reinforced Concrete Column-Steel Frame Ring Beam Joint

DAI Yan NIE Shaofeng ZHOU Tianhua

2019, 47(5): 110-122. doi:10.12141/j.issn.1000-565X.180505

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In this paper，a circular steel tube-confined Hsteel reinforced concrete columnsteel frame ring beam joint was designed，and a fullscale three-dimension finite element analysis model of the specimen was established． Then，the hysteretic curves，skeleton curves and failure modes of the specimens were calculated，and the results were compared with those obtained by experiments，with good accordance being found． Moreover，a finite-element variable parameter analysis was carried out to reveal the effects of axial compression ratio，concrete strength and line stiffness ratio on the seismic behavior of specimens． Finally，an improved node form of beam end-weakening flange was put forward． The results show that ( 1) with the increase of axial compression ratio，the energy dissipation and ductility of the specimen decrease significantly; ( 2) the change of concrete strength has little effect on the hysteretic behavior of specimens; ( 3) the bearing capacity，ductility and seismic energy dissipation performance of the joints all increase significantly with the increase of beam-column linear stiffness ratio when the column section remains unchanged and only the steel beam size varies; ( 4) when the section of steel beam remains unchanged and the steel content in the column varies，the change of seismic behavior of the joint with the line stiffness ratio of beam to column is not obvious; and ( 5) the adoptin of beam end-weakening flange helps to move the plastic hinge far away from the joint area without remarkably reducing the bearing capacity and energy dissipation performance of the specimen，thus protecting the joint area more effectively． The above-mentioned relevant conclusions lay a theoretical foundation for the application of this new type of joint．

Double Infiltration Model of Fractured Soil and Its Influence on Slope Stability

HAN Tongchun HE Lu LIN Bowen SU Yuqin

2019, 47(5): 123-129，138. doi:10.12141/j.issn.1000-565X.180413

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Under rainfall condition，the existence of fractures provides advantage for rainfall infiltration which may lead to the uneven distribution of rainwater，and the fractures are preferentially saturated，thus a head difference forms between the fracture network and the matrix and，furthermore，a water flow exchange occurs． In this paper， by representing the fractured soil as a dual-porosity system consisting of fractured network and matrix，the pressure head distribution of the matrix and the fracture network are obtained based on the Richard seepage equation of double-pore model and the Galerkin method，and the results are compared with those of Hydrus-1D，with the rationality of the method being verified． It is shown that ( 1) the wet peak surface distribution of the matrix is different from that of the fracture network，the former is steep while the latter is gentle; ( 2) the wider the matrix，the greater the effect of rainwater infiltration on the slope stability; and ( 3) when the matrix width becomes smaller， the rainwater infiltration is more and more uniform，and the depth of slope stability affected by rainwater infiltration becomes smaller，while the increase in saturation makes the shear strength of shallow soils decrease more．

Effects of Roughness on Interfacial Bonding Properties Between Concrete and FRP

YIN Yushi FAN Yingfang GUO Xinyan

2019, 47(5): 130-138. doi:10.12141/j.issn.1000-565X.180422

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In order to reveal the influence of concrete roughness on the interfacial bonding properties between CFRP and concrete，the roughness of concrete was quantitatively assessed through the sand-pouring method，the single shear test of CFRP-concrete interfaces were completed under 6 different conditions of interfacial roughness， and the influences of concrete roughness on the ultimate bond force，bonding strength and bonding slipping curve of the CFRP-concrete interface were investigated，finding that，as compared with the specimen with a roughness of 0. 25，the specimen with a roughness of 0. 44 possesses the best interfacial bonding property，and its ultimate bond force and strength improve by 36% ～ 51% and 124% ～ 221% ，respectively． Then，a model to calculate the effective bonding length of interface was established on the basis of the roughness parameters． From this model，it is found that ( 1) the effective bonding length of six surfaces generally decreases with the increase of roughness; ( 2) the bonding slipping curves of the samples remain consistent in rigidity in the brittle area，and the rougher the interface，the shorter the brittle section; and ( 3) in the plastic stage，the bonding slipping curves of the samples with 6 interface types slide with different slopes，eventually resulting in a stripping damage at a slipping value of 0. 04 ～ 0. 37mm

Influences of Different Factors on Strength of Alkali-Activated Fly Ash Mortar and the Corresponding Mechanism Analysis

LI Fuhai HU Dinghan HU Zhiming JIN Hesong FENG Zhihua WANG Yibin YU Yongjiang

2019, 47(5): 139-146. doi:10.12141/j.issn.1000-565X.180424

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This paper investigates the pore structure characteristics of alkali-activated fly ash mortar affected by different factors via a mercury intrusion test，and explores the mechanical properties of specimens from the view of pore structure characteristics． Test results indicate that ( 1) with the growth of curing age，the porosity of alkaliactivated fly ash mortar specimens increases，the average pore diameter decreases，and the distribution of internal pores changes from a discrete macroporous structure to a more uniform form; ( 2) both the curing temperature and the mass ratio of the excitant have an impact on the strength of specimens and the distribution of pore diameter， concretely，higher curing temperature may result in more fully hydration of fly ash，and the internal aperture of the structure may decrease with the growth of curing age，thus resulting in a higher compressive strength of the specimens; and ( 3) in the several above-mentioned factors，mass ratio has the most complex effect on pore structure， concretely，a continuous variation of mass ratio may result in a periodic change of pore structure distribution and compressive strength．

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