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    25 November 2016, Volume 44 Issue 11
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    Chemistry & Chemical Engineering
    Effect of Monoglyceride Amount on Physical Properties and Crystal Texture of Organogels
    LIU Guo-qin NAN Yang LIU Xin-qi
    2016, 44(11):  1-6.  doi:10.3969/j.issn.1000-565X.2016.11.001
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    In order to reveal the effect of monoglyceride dosage on the physical properties and crystal texture of organogels,a texture analyzer,a rheometer,a pulse nuclear magnetic resonance spectrometer,a differential calorimeter scanner and a X-ray diffractometer were adopted to evaluate the rheological properties,solid fat content,melting properties and crystal morphology of organogels.The results show that the change of monoglyceride content can change the number and type of crystals,thus changing the physical properties of organogels from a macro perspective.Through the analysis of the strength,hardness and crystal shape of the system,it is found that the organogel prepared at 80℃ and 12% of monoglyceride amount shows a better structure performance and can meet the actual production needs and applications.

    A Salting-Out Extraction Technology of Bio-Oil in Liquefaction Products of Lignin
    OUYANG Xin-ping CHEN Jing QIU Xue-qing
    2016, 44(11):  7-11,25.  doi:10.3969/j.issn.1000-565X.2016.11.002
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    The bottleneck in preparing lignocellulosic biomass liquid fuel is how to depolymerize lignin and separate the bio-oil obtained through the depolymerization.In this paper,a new technology of salting-out extraction for separating bio-oil from the liquefaction products of lignin is investigated,and the effects of the kind and dosage of inorganic salt,the equilibrium time and the temperature on the yield of bio-oil from the liquefaction products of lignin are revealed.The results show that the extraction of bio-oil is facilitated by taking saturated MnSO4 solution as the salting-out agent,and that,under the conditions of 10 min of equilibrium time and 80℃ of extraction temperature,the bio-oil yield is up to 52.47% with a salt content of 2.76%.This new technology avoids the use of organic solvents,and thus saves the cost for the recovery of organic solvents.Meanwhile,it helps eliminate the environmental pollution and the corresponding potential risk,which results from the volatilization of organic solvents.Therefore,this new technology provides a green approach for separating bio-oil from the liquefaction products of lignin.

    Hydrogen Production of Photo-Catalytic Water Splitting by Using Co3O4 Encapsulated Within TiO2 Nanotubes
    LI Xin-jun ZHANG Jia-feng YANG Xu LIAO Shi-jun
    2016, 44(11):  12-18.  doi:10.3969/j.issn.1000-565X.2016.11.003
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    By means of vacuum-assisted impregnation,cobalt nitrate was dipped into TiO2 nanotubes and then calcinated at 400℃.Thus,the photo-catalyst of Co3O4 nanoparticles embedded in TiO2 nanotubes ( TNT) was obtained.The material was characterized by means of XRD,TEM,XPS and UV-Vis spectroscopy,and through the hydrogen production of photo-catalytic water splitting,the photo-catalytic activity of the material was evaluated under a visible-light irradiation.Experimental results show that ( 1) highly-dispersed Co3O4 is embedded within TNT,and its size is 3 ～ 5 nm; ( 2) as compared with the Co3O4 catalyst supported on the exterior surface of TNT,the Co3O4 catalyst confined within TNT shows an enhanced interaction with TNT; and ( 3) the Co3O4 catalyst confined within TNT also shows an enhanced visible light absorption,and it increases the hydrogen production of water splitting under the visible light illumination significantly.

    Comparison of Exergoeconomic Costs of Cooling Methods in District Cooling Systems
    LI Ya-jun LIANG Wen-hao HU Ren-tian
    2016, 44(11):  19-25.  doi:10.3969/j.issn.1000-565X.2016.11.004
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    To choose what kind of cooling method in district cooling systems ( DCS) and how to choose have become hot topics in the DCS engineering field.In this paper,two exergy analysis models of steam absorption cooling system ( SACS) and electric compressor cooling system ( ECCS) are constructed,and on the basis of the two models,the two cooling systems are comparatively investigated by taking the minimum unit cooling exergoeconomy cost as the objectives.The results show that,when the two cooling systems have the same exergoeconomic cost,steam transport distance decreases as the ratio of steam exergy price to electricity price increases,and that,when the ratio is above 1.13,the exergoeconomy cost of SACS is always higher than that of ECCS.Therefore,an appropriate cooling system should be chosen by taking into consideration the steam transport distance,the electricity price and the steam exergy price.

    Chemical Structure of Enzymatic Hydrolysis Lignin from Corn Stover and its Application in Epoxy Composite
    ZHENG Da-feng LI Xiao-kang YU Fan-zhe CHEN Ran
    2016, 44(11):  26-32.  doi:10.3969/j.issn.1000-565X.2016.11.005
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    The chemical structure of the enzymatic hydrolysis lignin ( EHL) from corn stover was characterized by means of UV spectroscopy,infrared spectroscopy,elemental analysis,headspace gas chromatography and potentiometric titration.It is found that there exist more substituents in the aromatic ring of the EHL,and β-O-4 linkage is of lower fracture degree,and that,the main structural unit was H-type,and the methoxy group,phenolic hydroxyl group and carboxyl contents of the EHL are respectively 6.50%,0.48% and 2.46%.By mixing the lignin and the epoxy resin to prepare the EHL /epoxy resin composite,it can be concluded that the EHL within a certain dosage can improve the tensile strength and bending strength of the EHL /epoxy resin composite,and the heat resistance of the EHL /epoxy resin composite increases with the EHL dosage,and that at 460℃,the residual amount of the epoxy resin composite containing 2.0% EHL is 8.3%,while the residual amount of pure epoxy resin is only 4.4%.The above-mentioned results show that the EHL can improve the mechanical properties and heat resistance of epoxy resin significantly,so it has a good application prospect in epoxy resin composites.

    Investigation into Response Surface Methodology for Oxalate Formation During Oxygen Delignification
    LI Hai-long LIU Ying-ying LIU Meng-ru
    2016, 44(11):  33-40.  doi:10.3969/j.issn.1000-565X.2016.11.006
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    The oxalate formation of the kraft pulp with different influence factors ( namely time,temperature,oxygen pressure and alkali charge ( NaOH mass fraction) during an oxygen delignification process was investigated by single-factor experiments.On this basis,the Box-Benhnken experiment of the response surface methodology was conducted to optimize the main factors influencing oxygen delignification.The results show that,under the condition of 0.2% MgSO4 and 10% pulp consistency,optimal oxalate formation conditions during the oxygen delignification are a temperature of 100℃,an alkali charge of 1.5%,a reaction time of 60 min and an oxygen pressure of 0.5MPa.Under the optimal conditions,the oxalate content is 0.25 g /L and the ratio of the Kappa number difference to the viscosity difference is 0.045.

    An Integrated Process of Using Pressure Energy of Natural Gas to Generate Electricity and Produce Dry Ice
    XU Wen-dong CHEN Zhong LI Xia-xi XING Lin-lin QIAN Di QIN Zhen
    2016, 44(11):  41-48.  doi:10.3969/j.issn.1000-565X.2016.11.007
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    In view of existing technical problems and practical difficulties in the process of utilizing the pressure energy of natural gas as well as dry ice market demands,a new integrated process of using the pressure energy of natural gas pipeline network to generate electricity and produce dry ice is proposed.This process can help realize the power balance of isolated networks by coupling the expansion,power generation and compression processes,and it has a flexible operation,a high utilization efficiency of pressure energy and a low cost of outputting dry ice.By using the proposed process to analyze the gas usage situation in a city,it is found that,when the users’power changes within the range of 30%～ 60% of the generator output power,this process can steadily produce 84 kg /h of dry ice through a splitter.By means of both the unit operation-based exergy analysis of the proposed process and the diagnosis of EUD,it is concluded that the exergy efficiency of the proposed process can reach up to 59.40%,and both the expander and the compressor have more exergy loss.In addition,two exchangers are the weak points of this process and it is,therefore,suggested that the design of heat transfer enhancement process should be further improved.

    Analysis of Combustion Characteristics of Coal Chars in O2 /CO2 via a Modified Discrete Random Pore Model
    FEI Hua LI Pei-sheng ZAHNG Ying
    2016, 44(11):  49-55.  doi:10.3969/j.issn.1000-565X.2016.11.008
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    The combustion characteristics of the Xiaolongtan lignite and Jiaozuo anthracite chars in O2 /CO2 were investigated by using a thermogravimetric analyzer.On the basis of the key relationship between the reaction rate and the pore surface area of coal chars,the effective reaction surface area of coal chars during the combustion was revised in a small increment of time,and a stochastic differential equation is solved by means of differential increment analysis method.Finally,a modified discrete random pore model was constructed to analyze the combustion characteristics of the Xiaolongtan lignite and Jiaozuo anthracite chars in O2 /CO2 at different temperatures.By comparing the modified model with the existing discrete random pore model,it is found that the modified model has a better prediction results during the whole combustion process of coal chars,while the values predicted by the existing discrete random pore model show a larger deviation from the experimental data at the later combustion stage.

    Investigation into Depolymerization Characteristics of Alkali Lignin by Formate Cooperated with Pd /C
    ZHAO Yuan-yuan WU Shu-bin LI You-ming
    2016, 44(11):  56-62.  doi:10.3969/j.issn.1000-565X.2016.11.009
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    In order to explore the depolymerization characteristics of alkali lignin in the hydrothermal system with formate and Pd /C,seven kinds of formates were selected to conduct experiments.The results show that optimal conditions are a nickel formate and Pd /C amount ( with respect to raw material) of 10%,a reaction time of 30min and a reaction temperature of 325℃,and under such conditions,the liquid product yield in depolymerization products is 56.24% and the overall yield of four monophenols is 12.14%,By comparing high resolution mass spectra,organic elements and thermogravimetric characteristics of the control sample with those of the sample with nickel formate and Pd /C,it is found that the addition of nickel formate and Pd /C is helpful in the deoxygenation process of hydrothermal reaction of lignin,and causes more products of smaller relative molecular mass to produce.

    Mechanical Engineering
    Analysis of Dynamic Characteristic of Transient Impact from Hydraulic Hammer
    DING Wen-si TIAN Li LIU Kun
    2016, 44(11):  63-70.  doi:10.3969/j.issn.1000-565X.2016.11.010
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    On the basis of the transient stress wave propagation theory of one-dimensional vibration elastomer,a model is constructed to calculate the coaxial longitudinal collision of double flexible rod during the impact of hydraulic hammer drill rod on the corresponding piston.Then,the displacement-time transient response impact function of each impact part is solved by means of the eigenvalue expansion method of transient wave function,and the stress wave propagation rules of both the drill rod and the piston as well as the dynamic characteristics of each crosssection of both the drill rod and the piston are analyzed.Furthermore,the transient dynamic responses of impact parts with different drill rod lengths and diameters as well as with different initial speeds of piston are discussed.The results indicate that ( 1) drill rod length slightly affect the impact force and a short drill rod may result in a fast rebound of the piston; ( 2) with the increase of drill rod diameter,the impact force amplitude increases and the crushing ability improves,which means a relatively low energy efficiency; and ( 3) with the increase of the initial piston speed,the impact force proportionally increases and the crashing ability of hydraulic hammer greatly improves.These results can provide a theoretical basis for an optimization of the structure and performance of hydraulic hammers as well as a reasonable adjustment of construction parameters.

    Numerical Simulation of Residual Stress Relaxation of Shot Peening Under Cyclic Loading
    WANG Jian-ming LIU Xing-rui Lü He-ting
    2016, 44(11):  71-77,112.  doi:10.3969/j.issn.1000-565X.2016.11.011
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    The residual compressive stress field induced by shot peening can effectively improve the fatigue resistance of materials.However,the residual stress isn't constant,and its relaxation phenomenon caused by cyclic loading will reduce the effects of the shot peening on the fatigue resistance of materials.In order to conveniently and quickly achieve a residual stress field in a stable state,a numerical method to predict the residual stress relaxation under cyclic loading is proposed,and then it is used to achieve the stable residual stress fields of 7075 aluminum alloy specimens under different shot peening intensities and different load strengths.It is found that the simulation results accords well with the experimental results obtained through X-ray diffraction method.Thus,the correctness of the proposed numerical method is verified.In addition,the proposed numerical method is also applied to revealing the influences of the cycle numbers of loading,the stress ratios,the initial residual stress field and the plastic strains caused by the shot peening on the residual stress relaxation induced by the shot peening.

    Optimal Design of Wireless Power Transmission System for Micro Robotic Capsules
    LI Min LIU Dan LIU Xiu-quan
    2016, 44(11):  78-83.  doi:10.3969/j.issn.1000-565X.2016.11.012
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    The performance of wireless power transmission system for micro robotic capsules is affected by many factors,such as resonance frequency,coupling co-efficient,coil turns,coil radius,compensation capacitor and mutual inductance.In order to achieve a global optimum of the system performance,the system transmission efficiency should be improved and the minimum power requirement of micro robotic capsules should be met.Meanwhile,the system stability,the safety of temperature rise,the reliability and the volume should also be considered.In this paper,an energy efficiency model is constructed for the wireless power transmission system with series compensation on both primary side and secondary side.Then,with the coil turns and coil radius of the two sides and the resonance frequency as the variables,an objective function of the optimization problem is established to perform the optimal design of the wireless power transmission system.Finally,an improved genetic algorithm is utilized to solve the multi-variable and nonlinear constrained optimization problem.Experimental results indicate that the proposed optimization method is correct and effective,and a prototype of the wireless power transmission system designed for micro robotic capsules achieves an energy efficiency of 86.6mW with an efficiency of 8.01%.

    Optimization and Validation of Hypoid Pinion Roughing Summary Based on Tilted Method
    SU Jin-zhan GUO Xiao-dong LIU Yong-sheng ZHANG Wei-qing
    2016, 44(11):  84-89.  doi:10.3969/j.issn.1000-565X.2016.11.013
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    In order to improve the uniformity of finishing allowance of hypoid pinion cutting by tilted method,an optimization method of roughing summary of the pinion is proposed.In this method,on the basis of known pinion finishing summary,the location of both tooth flanks can be determined according to the pinion tooth size at the middle of gear blank face width.Then,by presetting the initial roughing summary and finishing allowance of the pinion,the finishing allowance of ten control points in both tooth surfaces is achieved.Finally,a genetic algorithm is adopted to conduct an optimization,with the minimum sum of the squares of the difference between the preset finishing allowance and the finishing allowance as the objection function and with the roughing summary of the pinion as the variables.Numerical examples show that,as compared with the Gleason's method,the proposed method decreases the maximum deviations of the finishing allowance on concave and convex by 0.015 and 0.123mm as well as the corresponding root mean squares by 9.52% and 7.98%,respectively.In addition,the measured normal chordal thickness at the toe,middle and heel of a tested pinion decrease respectively by 0.11,0.06 and 0.12mm.The above results demonstrate that the uniformity of the finishing allowance is improved greatly.

    A New Cushion Device for High-Speed Pneumatic Cylinder and its Performance
    ZHANG Ri-hong DU Qun-gui
    2016, 44(11):  90-96.  doi:10.3969/j.issn.1000-565X.2016.11.014
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    For the cushion device of the high-speed pneumatic cylinder with a pressure release valve,the speed variation range of pneumatic cylinder piston is narrow,and to achieve optimum cushion conditions is difficult.The main reason is high compressibility of gas.Specifically,when the opening conditions of the pressure relief valve are met,it cannot always keep open before the cylinder arrives at a stroke,and thus the phenomenon of repeated opening and closing is universal.At the same time,the exhaust speed of the valve cannot adapt with the running speed of the piston.In order to solve these problems,a new cushion structure mainly composed of pressure release cushion components and adjustable clearance components is proposed.Then,through the simulation analysis,it is demonstrated that when the mass of moving parts in the pneumatic cylinder is 6 kg,a better cushion for the top speed of the pneumatic cylinder within the range of 2.3 ～ 3.7m/s can be achieved by means of the segmented regulation of both the spring compression amount of the pressure release valve and the clearance volume of the back pressure cavity.Finally,at a maximum velocity of pneumatic cylinder piston of 3.0 m/s,a further simulation is performed by changing the mass of moving parts.It is found that the new cushion structure still has better cushioning and regulating performance when the load mass is changed.

    Preparation and Tribological Properties of HFCVD-Based Freestanding Thick Diamond Film
    FENG Wei YANG Bin LU Wen-zhuang
    2016, 44(11):  97-102.  doi:10.3969/j.issn.1000-565X.2016.11.015
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    A crystal growth model of freestanding thick diamond film was discussed,and on the basis of this model,a self-standing thick diamond film slice of a thickness of about 0.6mm was prepared by means of HFCVD ( Hot-Filament- Assisted Chemical Vapor Deposition) method.Then,a friction experiment of the film slice was conducted on a ball-disc tribometer,and the tribological properties of the film slices respectively with a steel ball,a ceramic ball and an aluminum ball as the friction pair were characterized by using a SEM and a Raman spectrometer.The results show that ( 1) when the friction pair is an aluminum ball,average friction coefficient is the biggest and metal transfer layer appears very fast in the initial stage of grinding; ( 2) when the friction pair is a ceramic ball,the average friction coefficient is the smallest and the ball surface material is in a fine clastic distribution; and ( 3) the wear of the film slice is very small after the experiment,which means that the film slice is a good wear-resistant material.

    Analysis of Work Mechanism of Variable Pivot Journal Bearing and Experimental Investigation into Vibration Characteristic of Rotor
    YANG Qi-jiang LI Wei-guang ZHENG Xiang-li WANG Kai
    2016, 44(11):  103-112.  doi:10.3969/j.issn.1000-565X.2016.11.016
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    In this paper,a new variable pivot structure of three-pad tilting pad sliding bearings is developed by replacing traditional tilting pad bearing mechanical pivots with fluid pivots.The forming principle of inner and outer layer films of the new fluid pivot bearing is described,and the initial work state of the bearing is analyzed.Then,the position of the bearing equilibrium under the initial work state is simulated,and the relationship between pad floating-required hydrostatic chamber area and static bearing load as well as rotor speed is expounded.In order to investigate the dynamic performance of the bearing and achieve test parameters,a test bench of journal bearing-rotor vibration characteristic is developed,which can perform automated data acquisition,real-time data analysis and other functions.Furthermore,both the double-sided balancing and the influence coefficient method are adopted to conduct a field rotor balancing test on the developed bench,and it is found that the proposed method in this paper is effective.Finally,the traditional journal bearing is compared with the variable pivot journal bearing in terms of rotor vibration characteristic and test bench machine feet acceleration vibration characteristic,finding that the developed bearing has a better damping characteristic.

    Modeling and Compensation of Absolute Positioning Error of Industrial Robots
    QI Jun-de ZHANG Ding-hua LI Shan CHEN Bing
    2016, 44(11):  113-118.  doi:10.3969/j.issn.1000-565X.2016.11.017
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    In order to improve the absolute positioning accuracy of robots,an absolute positioning error model is constructed and an error compensation method is investigated.First,positioning errors are divided into geometrical parameter errors and compliance errors,and two models are respectively constructed for the two kinds of errors.The geometrical parameter errors are investigated on the basis of modified Denavit-Hartenberg kinematics,and the impact of the compliance errors is decoupled.Then,by taking into consideration the conversion error between the base coordinate system and the measurement one of robots,a geometrical parameter error model on the basis of relative positions is constructed.For the compliance errors,a model for joint 2 and joint 3 is constructed according to the construction features of robots,thus simplifying the calculation model of the compliance errors greatly.Finally,on the basis of the two kinds of error models,the error compensation method is proposed.The results of error compensation experiments show that average absolute positioning accuracy decreases from 1.173 to 0.158mm after calibration,which means that the proposed method can improve the absolute positioning accuracy of industrial robots effectively and extend its range of applications greatly.

    Power & Electrical Engineering
    Probability Model and Risk Assessment of False Tripping of Traveling Wave Protection on UHVDC Transmission Lines Under Thunder Strike
    CAI Ze-xiang LIANG Yi TIAN De-liang LI Xiao-hua LI Shu-yong
    2016, 44(11):  119-125.  doi:10.3969/j.issn.1000-565X.2016.11.018
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    There exists a false tripping risk in the traveling wave protection on UHVDC transmission lines under thunder strike,and simply increasing the set value may cause an action failure when high resistance earthing happens.In order to solve these problems,a probability model to analyze how the traveling wave protection falsely trips on UHVDC transmission lines under thunder strike,is constructed by using the parameters including the thunderbolt rate on transmission lines,the shield failure rate,the distribution probability of wave fronts and the false tripping section of traveling wave protection on the basis of thunder strike location.Then,malfunction probability is calculated on the basis of superposition principle,and malfunction frequency is obtained from the data of lightning activity.Furthermore,by adopting the two indicators,the risk assessment of the false tripping is performed.Finally,by taking a UHVDC transmission line of China Southern Power Grid as an example,the proposed method is verified by using both actual parameters and wave recording data,finding that the results accord well with the practical engineering statistics ones.

    Effect of Liquid Layer Thickness on Thermocapillary Convection in an Annular Two-Layer System Subjected to a Bidirectional Temperature Gradient
    PENG Lan WEI Cheng-xing-yun LIU Jia
    2016, 44(11):  126-132.  doi:10.3969/j.issn.1000-565X.2016.11.019
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    The liquid layer thickness plays an important role in the thermocapillary convection of liquid layer system.However,most of previous researches focused on the convention caused by a mono-directional temperature gradient.In this paper,the effect of the liquid layer thickness on the thermocapillary convection in an annular twolayer system subjected to a bidirectional complex temperature gradient is investigated by a set of two-dimensional numerical simulations.In the simulations,the system bottom is heated by following a linear temperature profile,and the free surface convects with outer space.Moreover,the liquid layer thickness ratio Hr changes from 0.1 to 0.9,the range of the radial temperature difference Re is 0 ～ 1.5 ×106,and the thickness radial ratio Γ is 0.1,0.2,0.3.The results show that ( 1) when Re is smaller,there exists an axisymmetric steady flow,and the thermocapillary convection decreases with the increase of Hr ; ( 2) an unsteady multi-cellular flow occurs as Re increases and then exceeds a critical value,and both the amplitude and the convection decrease with the increase of Hr ; ( 3) the critical value changes with Hr in a non-monotonic way; and ( 4) when Hr locates between 0.5 and 0.7,the critical Re is always the biggest at different Γ,and the system is in the most stable state.

    Load Probability Analysis and Energy Storage Optimization of Distribution Networks of PV Generation
    XIA Cheng-jun LIANG Jun-jun SONG Xu-dong YU Nan-hua
    2016, 44(11):  133-139.  doi:10.3969/j.issn.1000-565X.2016.11.020
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    The PV access to distribution networks can cause the volatility and uncertainty of load to increase,which has a certain effect on the capacity planning of power transmission and distribution equipment.In this paper,on the basis of the probability analysis of both PV power and load in longitudinal moment,supply load is reduced by introducing a risk parameter.Then,energy storage is taken as a measure to shift electricity from peak periods to offpeak periods,so as to handle the probabilistic risk after reducing the supply load.On the basis of this principle,the energy storage capacity is optimized,and the balance between risk and economics as well as the risk factor corresponding to a maximum economic benefit is achieved.Case analyses show that the proposed method in this paper can bring certain economic benefits for the device capacity planning of distribution networks.

    A Real-Time Solar Radiation Intensity Calculation Model for Calculating Transmission Capacity of Overhead Conductor
    LIU Gang HE Geng-sheng LI Yang HAO Jin-bao QI Kun-lun TANG Jian-lin
    2016, 44(11):  140-146.  doi:10.3969/j.issn.1000-565X.2016.11.021
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    In order to explore the potential transmission capacity and overcome the defect that solar radiation intensity is regarded as a constant when the transmission capacity of overhead conductors is calculated,by adopting a solar radiation intensity gradient of 100W/m2,the influence of the solar radiation intensity on the transmission capacity of overhead conductors of different kinds of cross-sectional areas is discussed.Then,on the basis of the atmospheric attenuation law of solar radiation and by introducing an attenuation coefficient,a real-time solar radiation evaluation model is constructed.In the model,according to specific time and the longitudes and latitudes of different regions,the problem is converted into another problem of calculating the distance of the solar radiation getting through the atmosphere,thus realizing the purpose of evaluating the real-time solar radiation intensity of a region.Finally,by using the meteorological data of Datong,Shanxi Province in 2012 and the data calculated by the formulas of IEEE 738—2006,the accuracy of the constructed model is verified.It is found that the data calculated by this model can fit the meteorological data well,with a maximum error within 70W/m2,and the fit is better than the data calculated by the formulas of IEEE 738—2006,which means that this model can meet the requirements of calculating the transmission capacity of overhead conductors.

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