ISSN 0253-2778

CN 34-1054/N

2018 Vol. 48, No. 3

Display Method:
Original Paper
Nitrogen-rich a-MEGO@g-C3N4 coating on separator for advanced Li-S battery
DU Juan, JIN Song, DU Zhenzhen, JI Hengxing
2018, 48(3): 175-183. doi: 10.3969/j.issn.0253-2778.2018.03.001
Lithium-sulfur batteries are widely seen as a promising next-generation energy storage system owing to their ultrahigh energy density and environmental benignity, yet the low electrical conductivity of sulfur and the shuttle effect of dissolved polysulfides result in poor cycling performance. An a-MEGO@g-C3N4composite coated on polypropylene separator with high nitrogen content (atomic percent 20.08%) and specific surface area (1000 m2·g-1) was developed to inhibit polysulfide shuttling. The prepared lithium-sulfur battery with the a-MEGO@g-C3N4 coated separator delivered a specific capacity
Determination of α-tocopherol using positive scan polarization reverse catalytic voltammetry
SHI Tianyang, WU Shouguo, WEI Wei
2018, 48(3): 184-190. doi: 10.3969/j.issn.0253-2778.2018.03.002
Silver oxide nanoparticles were formed at the surface of a silver electrode with anodic polarization, then the carboxyl graphene-nanosheets were electrodeposited on the silver oxide with cyclic potential scanning, and the graphene/silver oxide/silver electrode was successfully prepared and applied in detection of α-tocopherol in the alkaline medium. The electrochemical behavior and the electrocatalytic activity of the modified electrode were investigated using cyclic voltammetry. The α-tocopherol was detected by means of this modified electrode and the positive scan polarization reverse catalytic voltammetry. The experimental results demonstrate that the thus-prepared modified electrode is stable and has high sensitivity. Two linear relationships between the difference value peak current and the α-tocopherol concentration are obtained in the range of 0.02~0.32 μmol/L and 0.32~4.0 μmol/L respectively, with a limit of detection reaching 0.01 μmol/L.
Preparation and characterization of polymer nanosheets by radical polymerization
LI Na, HU Xiaoqian, BAI Ruke
2018, 48(3): 191-198. doi: 10.3969/j.issn.0253-2778.2018.03.003
4-vinyl benzyl 4-oxo-4-((4-(phenylamino)phenyl)amino)butanoate (VPB) were designed and synthesized, and then polymer nanosheets were successfully prepared by self-assembly and polymerization of the VPB. Structures of the VPB and the polymer were characterized by HNMR spectroscopy and infrared spectroscopy. Self-assembly of the VPB and the polymers were investigated by transmission electron micrography and X-ray analysis. The results indicate that VPB can self-assemble into two-dimensional nanosheets in the mixed solution of toluene and acetone, and morever, VPB can be copolymerized with N-butyl maleimide to form a polymer nanosheet with a size of several micrometers and thickness of 2 nanometers. It has been demonstrated that the combination of self-assembly and free radical polymerization is a convenient and efficient approach for the preparation of polymer nanosheets.
Optimal weighted model for ensemble forecast of the surface air temperature in mainland China and its regional applications
SU Qihua, ZHOU Renjun, KE Zongjian, LIU Changzheng, DU Liangmin, YAN Yan
2018, 48(3): 199-209. doi: 10.3969/j.issn.0253-2778.2018.03.004
Based on Coupled Model Intercomparison Project,Phase5(CMIP5) muti-models, an optimal weighted model for ensemble forecast (Op-SE) of the surface air temperature in mainland China was presented. In order to assess the capability of Op-SE, it was compared with equally-weighted ensemble (EE) and superensemble (SE), and anomaly correlation coefficient (ACC) and root-mean-square-error (RMSE) were chosen to evaluate their forecasting skills. As shown from the results, ACC between Op-SE and observation is optimal in most of China, especially eastern China, which indicates that ACC has passed the significance test at 0.5 level. However EE has poor performance in ACC. As for RMSE, EE is also relatively weak. And Op-SE is better than SE in eastern China, while SE is better in a few other areas like Sichuan Basin. The comprehensive assessments of ACC and RMSE show that the forecast skill of Op-SE is best in northeast, north, eastern, southwest and northwest of China, but is not good enough in Sichuan Basin and southern Gansu. In conclusion, Op-SE provides a new method on selecting outstanding models into ensemble climate forecast, which can improve the forecast skill in regions to some extent.
Pollution characteristics and health risk assessment of volatile organic compounds in Hefei urban area
WANG Xin, ZHANG Min, ZHANG Fuhai, LIU Guijian
2018, 48(3): 210-220. doi: 10.3969/j.issn.0253-2778.2018.03.005
The ambient VOCs were monitored in the urban area of Hefei city during four seasons in 2016. They were analyzed using an off-line analysis method of SUMMA cannister sampling and gas chromatography-mass spectrometer(GC-MS). The VOCs results show that 48 VOCs are identified in the air samples including alkane, arene, halohydrocarbon, etc. The annual mean concentration of total VOCs (TVOCs) is 15.61×10-9, the largest one reaching 47.64×10-9. The seasonal variation of TVOCs in this area is obvious, and the order is winter>spring>autumn>summer; the daily mean concentration of TVOCs shows a trend of concentrations being higher in the morning and in the evening, and lower at noontime. Non-carcinogenic risk indexes of VOCs are below 1, which would not cause non-carcinogenic health hazards to exposed populations. However,the cancer risk index exposed to carcinogenic VOCs is higher than the suggested value of USEPA(U. S. Environmental Protection Agency)( 1×10-6 ), which could indicate a relatively higher cancer risk.
Experimental study on three new floating bed plants for purifying eutrophic water
ZHANG Zerui, ZHANG Xuefei, GUO Jing, WANG Jiaquan
2018, 48(3): 221-228. doi: 10.3969/j.issn.0253-2778.2018.03.006
To seek for new floating bed plants which can efficiently purify eutrophic water, three kinds of terrestrial plant with medicinal value and greening effect, Rumex acetosa, Ophiopogon bodinieri and Ophiopogon japonicus were selected as the floating-bed plants for outdoor experiments. The self-designed ecological floating-bed was used as the plants carrier. The eutrophic waste water which consisted of lake water and a certain amount of nutrients was put under treatment for 40 d. The growth of the plants and the purification effect were compared . The results show that all three plants can survive, and that Rumex acetosa grows faster and its biomass increases more, but its growth period is short, while Ophiopogon bodinieri and Ophiopogon japonicus are the evergreen plants. At the end of the experiment, the removal rate of total phosphorus by Rumex acetosa is 90%, while that of the other two plants is about 40%. The purification rate of ammonia nitrogen by Rumex acetosa is higher than that of Ophiopogon bodinieri and Ophiopogon japonicus. As time goes by, the ammonia nitrogen removal rate by the three plants can reach about 90%; the removal rate of total organic carbon by Rumex acetosa is 80%, while the removal rate by Ophiopogon bodinieri and Ophiopogon japonicus is 60%~70%. It has been shown in this paper that Rumex acetosa, Ophiopogon bodinieri and Ophiopogon japonicas can be used as floating bed plants, and that they can be selected according to different ecological conditions and the degree of water pollution. This has important practical significance for the development of new varieties of floating bed plants.
Effect of defocusing distance along Z axis on laser cladding forming
2018, 48(3): 229-235. doi: 10.3969/j.issn.0253-2778.2018.03.007
The variation of distance between laser head and substrate (named defocus distance) has a considerable effect on powder utilization efficiency and energy density, therefore affecting the laser cladding forming (LCF) process. Orthogonal experiments L16 (44) of the four parameters: laser power, scanning speed, gas flow rate and defocusing distance and single factor experiment of the defocusing distance along Z axis were conducted to investigate the coupling effects of these parameters on LCF process. The result of orthogonal experiment suggests that all four parameters play important roles in LCF, and the order of factors which affect the cladding efficiency is: laser power>gas flow rate>defocusing distance>scanning speed. The result of the single factor experiment indicates that the optimal cladding quality occurs when the defocusing distance reaches a certain level. The maximum cladding layer height can be achieved when the defocusing distance is 5mm. The cladding layer height is reduced when the defocusing distance is less or larger than 5mm. It is proved that the powder utilization efficiency gradually increases and then decreases when the defocusing distance keeps increasing.
Large eddy simulation of turbulent swirling flow based on the swirling-strength subgrid scale stress model
XIA Zhaoyang, ZHANG Hongda, YU Zhou, YE Taohong, TANG Peng
2018, 48(3): 236-245. doi: 10.3969/j.issn.0253-2778.2018.03.008
To enhance the ability of large eddy simulation (LES) to predict turbulent swirling flow, a subgrid eddy viscosity model based on the swirling-strength was applied to the LES of the non-reactive flow of the Sydney swirl burner. Two operation conditions, high Reynolds number with low swirl number and low Reynolds number with high swirl number, were selected to validate the performance of the proposed model in the strong shear layer and swirling flow, and the model simulation results were compared with the dynamic Smagorinsky model (DSM) and experimental results. The simulation results show that the LES results based on the swirling-strength model (SSM) can reasonably predict the important characteristics of the recirculation zone and precession motion of the central jet, which indicates the SSM model results of statistical moment are better than the DSM model results. However, the prediction of the RMS values at the shear layer of swirling flow is higher than experimental data, which indicates that the kinetic energy dissipation of SSM model may be over predicted in the shear layer, and that the SSM model needs to be improved in future.
Experimental investigation on the effect of dilution on the liftoff and blowout characteristics of jet diffusion flame
YAN Ye, JIANG Nianpeng, ZHANG Haitao
2018, 48(3): 246-252. doi: 10.3969/j.issn.0253-2778.2018.03.009
On the background of combustion utilization of low calorific value gas fuel, methane or propane diluted by N2 or CO2 and nozzles of 2mm or 3mm inner diameter are set as multiple experimental variables. The liftoff and blowout velocities of jet diffusion flame varying with the diluent concentration were experimentally investigated. With the increase of the diluent concentration, the liftoff velocities slowly decline almost linearly, while the blowout velocities quickly decrease nearly exponentially. The analysis shows that the tendencies may be attributed to the decreases in the stoichiometric laminar burning velocity, the original fuel mass fraction and heat release. Suggestions on the design of burner utilizing low calorific value gas fuel are proposed. In addition, exceeding the critical diluent concentration, the attached flame is directly quenched instead of being a stable lifted flame with the increase of the jet velocity. According to the Reynolds numbers of methane and propane at each critical diluent concentration, it can be inferred that the two critical diluent concentrations of methane and propane are controlled by different mechanisms.
A calculation analysis for the ablation and heat transfer of carbon-based composite materials in combustible airflow environment
LIU Na, YING Wei, YANG Chi, JING Zhao, LI Xudong
2018, 48(3): 253-260. doi: 10.3969/j.issn.0253-2778.2018.03.010
To study the ablative heat transfer mechanisms of carbon-based composite materials in the aerodynamic heating environment of combustible airflow, an analysis of chemical reaction,thermal chemical ablation and thermal response for the materials was conducted,and a calculation method for the oxidative ablation and heat transfer of the materials was present. The comparison results signified that the ablation results obtained by the calculation method were consistent with the experimental results of flat and stagnation-point ablation tests. Using this method, the ablation and temperature-field differences of carbon-based composite materials in combustible airflow and air environments, and the effects of a variety of parameters concerning pressure and components on the ablation and heat transfer were obtained. In the same thermal environment, the material surface temperature under combustible airflow is lower than that of the air environment, and the ablation back quantity is higher than the results of the air environment; with the increase in H2O and CO2 content, surface temperature and the amount of ablation back show a tendency of decrease and increase, respectively, with H2O exhibiting a greater influence.