Journal of University of Chinese Academy of Sciences

Hadamard-type inequalities for products of (h, m)-convex functions and their applications

SUN Wenbing

2018, 35 (2): 145-153. DOI: 10.7523/j.issn.2095-6134.2018.02.001

In this paper, we established some new Hadamard-type inequalities for products of (h, m)-convex functions, which are the extended Hadamard-type inequalities for ordinary convexity sense, s-convexity in the second sense, m-convexity sense, and h-convexity sense.

Sympathetic cooling of Rb⁺ ions by cold Rb atoms in an ion-neutral hybrid trap

LÜ Shuangfei, JIA Fengdong, LI Xiaokang, LIU Jinyun, XU Xiangyuan, XUE Ping, ZHONG Zhiping

2018, 35 (2): 154-159. DOI: 10.7523/j.issn.2095-6134.2018.02.002

Abstract ( 328 ) PDF (KB) ( 3 )

Sympathetic cooling of Rb⁺ ions by cold Rb atoms is studied in an ion-neutral hybrid trap. The effect of a linear Paul trap (LPT) parameter q_1,2 on the sympathetic cooling is studied by measuring the changes in ion number N_i and temperature T_i after interaction with cold atoms. The sympathetic cooling effect is observed with 0.3 ≤ |q_1,2| ≤ 0.8. At the |q_1,2| value of 0.32, ions are cooled from initial (2 010±380) K to (325±35) K and the lifetime of ions is extended from 7 s to 15 s via sympathetic cooling. These findings are very useful for cooling of atomic and molecular ions, especially for the ions without available optical channels.

Trends of extreme temperature and precipitation in Ebinur Lake basin in Xinjiang during the period from 1957 to 2012

DING Zhiyong, GE Yongxiao, ABUDUWAILI Jilili, PU Jia

2018, 35 (2): 160-171. DOI: 10.7523/j.issn.2095-6134.2018.02.003

Abstract ( 405 ) PDF (KB) ( 2 )

The linear regression and Mann-Kendall abrupt change test methods are employed to analyze the temporal variability trends of 22 extreme climate indices in Ebinur Lake basin from 1957 to 2012. The results are given as follows. 1) From 1957 to 2012, most of the warm indices showed increase trends while summer days, annual maximum temperature and warm spell duration days non-significantly increased. Most of the cold indices had decrease trends, but daily minimum temperature and monthly minimum value of daily maximum temperature increased by 0.78 and 0.33℃/10 a, respectively. Except that consecutive dry days significantly decreased by 3.63d/10a, the precipitation indices showed increasing trends. 2) The amplitudes of changes in cold spell duration days, monthly minimum value of daily maximum temperature, and annual minimum temperature were larger than those of changes in warm spell duration days, monthly maximum value of daily minimum temperature, and annual maximum temperature,respectively. Changes in night extreme climate indices were greater than changes in daytime extreme climate indices. 3) Among atmospheric circulation patterns,AO had the highest influence on extreme temperature indices, followed by NAO and ENSO. These patterns had the most obvious influence on cold extreme indices, but slight effect on extreme precipitation indices in Ebinur Lake basin. 4) Except annual minimum temperature, the other warm indices showed significant positive correlation with annual mean temperature(AMT). Except monthly minimum value of daily maximum temperature and annual minimum temperature, which had significant positive correlations with AMT, the cold indices as well as diurnal temperature range showed significant negative correlation with AMT. Most of extreme precipitation indices had significant positive relationship with total annual precipitation.

Assessment of water resource pressure of Heihe River basin at the county level from 1995 to 2014

LUO Kaisheng, TAO Fulu

2018, 35 (2): 172-179. DOI: 10.7523/j.issn.2095-6134.2018.02.004

Abstract ( 343 ) PDF (KB) ( 1 )

Facing the great challenge of water shortage, assessment of water resources pressure has become a prominent issue. This study used the SWAT (soil and water assessment tool) model, Mann-Kendall detection method, and the 1995-2014 statistics of Heihe River basin to analyze the spatial and temporal dynamics of water resource pressure at the level of county. The assessment indicator system includes the total water resource pressure (TP), ecology consuming water pressure (EP), product consuming water pressure (PP), and domestic consuming water pressure (DP). The results show an obvious spatial variation in water resource pressur. Ganzhou has the largest TP, followed by Ejila and Shandan. The facts attribute to the high PPs in Ganzhou and Ejila and high EP in Shandan. Linze and Mingle have high TPs, close to 1. EPs presented decrease trends in Qilian, Sunan, Gaotai, Shandan, and Ejila in 1995-2014 and the maximum occurred in Suzhou. Other counties displayed increase trends and the maximum occurred in Suzhou. The increase trends of PP occurred in Linze, Gaotai, Sunan, Jiayuguan, Jinta, and Ejila in 1995-2014, and the decrease trends in Qilian, Sunan, Ganzhou, Shandan, and Mingle. These variations in water resource pressure were the comprehensive and interactive results of climate, population, vegetation, ecology, urbanization, and policies. The dynamic variations in different counties suggest that the decision makers adopt different policies in different counties in the basin. The present study illustrates the status of the water resource pressure at the county level, and provides an example for water resource assessment of arid and semi-arid basins.

Fast software implementation of SM4

LANG Huan, ZHANG Lei, WU Wenling

2018, 35 (2): 180-187. DOI: 10.7523/j.issn.2095-6134.2018.02.005

Abstract ( 853 ) PDF (KB) ( 3 )

SM4 is the national block cipher standard of China widely used in various information systems and security products.Some application environments have high demands for software implementation performance of cryptographic algorithms. Currently, SM4 software implementation is based on look-up table. Therefore, fast software implementation of SM4 algorithm has become an important research topic. This work investigates the software optimization implementation of SM4. Using SIMD technique, we present software optimization implementation of SM4, which has a significant advantage over current software implementation based on look-up table. On the Intel Core i7-6700 processor, the software performance improves by 1.38 times compared to implementation based on look-up table.

Water film heating evaporation under low pressure

WANG Chao, CHEN Xue, XU Ruina, JIANG Peixue

2018, 35 (2): 188-192. DOI: 10.7523/j.issn.2095-6134.2018.02.006

Abstract ( 402 ) PDF (KB) ( 2 )

A one-dimensional evaporation model for simulating water evaporation under vacuum condition is proposed by using Fick's diffusion law. Based on the correspondence between saturated water temperature and pressure, a method for determining the thickness of diffusion boundary layer is developed. An experimental system of water film low pressure heating and evaporation is set up. The vaporization and temperature variations of water film under different conditions are studied. By comparing the predicted results and experimental data for evaporation mass and temperature changes, it is found that the model accurately predicts the evaporation characteristics of water film under low pressure and heating conditions. Based on the current mathematical model, the effects of vacuum pressure, heating heat flux, and chamber volume on water evaporation rate and vapor pressure are further studied. The results indicate that the lower the pressure, the higher the heat flux, and the larger the chamber volume are, the higher evaporation rate is and the shorter time is needed to reach saturation.

Study on heterogeneity of pore structure to permeability by MRT LBM

MA Bin, SHI Lin, HUANG Chao, XU Qianghui

2018, 35 (2): 193-199. DOI: 10.7523/j.issn.2095-6134.2018.02.007

Abstract ( 243 ) PDF (KB) ( 4 )

Porosity and permeability are very important characters of a porous media.In this work, MRT LBM was used to study the pore structure influence on permeability and the porosity loss influence on permeability loss. Our simulation results are shown as follows. If there are some factors which cause even decreasing of porosity, such as that of depositing, sediment, and coking, the scope of permeability loss is larger than that of porosity loss. In same-porosity-different-structure (SPDS) porous media, there are extraordinary differences in permeability depending on their own pore structures.A larger ratio of max throat length to min throat length leads to a smaller permeability,and a larger tortuosity leads to a smaller permeability.

Numerical analysis of a novel spacer grid in rod bundles of PWR

LIANG Haoyu, WU Junmei

2018, 35 (2): 200-208. DOI: 10.7523/j.issn.2095-6134.2018.02.008

Abstract ( 423 ) PDF (KB) ( 3 )

Spacer grid is an important part of fuel assembly in reactor. The AFA-2G/3G spacer with mixing vane supports rod bundles well and enhances the heat transfer, but it has a complex structure and difficult processing. A novel spacer grid with the rectangular longitudinal vortex generators (RLVGs) is designed to improve thermal-hydraulic characteristics of fuel assembly. Based on the standard k-ε model with the enhanced wall treatment, a three-dimensional numerical simulation of the novel spacer grid in the channel of PWR fuel rods is presented. The effects of Reynolds number and attack angle are investigated. Numerical results show that the second flow generated by LVGs spreads to the downstream region of spacer grid and improves the heat transfer. The spacer grids with RLVGs with attack angles of 60° and 45° result in almost equal heat transfer performances. However, the spacer grid with RLVGs with attack angle of 60° brings about more pressure drop in comparison with that of the 45° case. The present research on new fuel assembly has certain potential value for the engineering design.

Characteristics of bending angles in process of the thermal transport of thermal cloaking system

XU Guoqiang, ZHANG Haochun, MA Chao, XU Yuting, ZHANG Chenxu

2018, 35 (2): 209-215. DOI: 10.7523/j.issn.2095-6134.2018.02.009

Abstract ( 318 ) PDF (KB) ( 3 )

Thermal cloak provides good behaviors of thermal protecting and cloaking, which leads to wide applications in the fields of aviation, transport, and computer. Currently, the design and study of thermal cloak are based on transformation optics, forcing the heat flux bypassing the protected obstacle. In this work, the heat flux, bending at random position of the thermal cloaking system in 2D domain, was obtained using transformation optics based on the form invariance of differential equations of heat conduction after coordinate transformation. FLUENT was employed to verify the bending angle of heat flux on the material layer boundaries. The results indicated that the thicker material layer led to the smaller bending angle. The bending angle increased with the ratio of conductivities b if b>1, and it reduced with the ratio of conductivities b if b<1. Hence, the heat flux path can be regulated with these findings, and the cloaking and protecting performances can be optimized.

Inverse method for retrieving high-temperature effective thermal conductivity of nanocomposite thermal insulation

LIU Hua, XIE Xiangqian, JIN Zicheng, XIA Xinlin, AI Qing, LI Donghui

2018, 35 (2): 216-221. DOI: 10.7523/j.issn.2095-6134.2018.02.010

Abstract ( 363 ) PDF (KB) ( 2 )

An experimental apparatus was built to measure transient thermal characteristics of nanocomposite thermal insulation within a temperature range between 290 and 1 090 K. An inverse method was developed to retrieve the temperature-dependent effective thermal conductivity based on transient temperature measurements. It was achieved by combining a forward model for solving combined conduction and radiation and an optimization method based on genetic algorithm (GA). The method was validated by numerical experiments. The temperature-dependent effective thermal conductivities of nanocomposite thermal insulation at normal pressure were retrieved by solving the inverse method. The retrieved value increased from 0.027 to 0.043 W/(m·K) as temperature increased from 290 to 1 090 K.

Investigating on photothermal conversion properties of plasmonic Ag nanofluids

CHEN Meijie, TANG Tianqi, LIU Ziyu, HE Yurong

2018, 35 (2): 222-226. DOI: 10.7523/j.issn.2095-6134.2018.02.011

Abstract ( 282 ) PDF (KB) ( 1 )

A calculation model incorporating the heat loss is used to study the photothermal conversion characteristics of Ag nanofluids in this work. Adding nanoparticles to the traditional working fluid enhances the light absorption and scattering to obtain better photothermal conversion abilities. The Ag nanofluid with a particle volume fraction of 2.5×10^-6 leads to the maximum temperature rise of 67.31℃, which is 1.8 times that of the base fluid. However, its photothermal conversion efficiency is 2.9 times that of the base liquid since the heat loss is taken into account in the calculation model. With the increase in particle concentration, the temperature rise and the photothermal conversion efficiency gradually increase, and the change rates of temperature rise and photothermal conversion efficiency become gradually small.

Experimental study of droplet coalescence on aluminum surface induced by pins

ZHANG Leigang, CHEN Zhenqian

2018, 35 (2): 227-232. DOI: 10.7523/j.issn.2095-6134.2018.02.012

Abstract ( 254 ) PDF (KB) ( 2 )

In this work, the phenomenon of the condensed droplets on a cooled aluminum plate after contact with pins was observed in the experimental study. The changes in radius of the droplet induced by the pins of different sizes at different times were observed and the radius of the cleaned area was cleared. The heat flux and heat transfer coefficient calculated based on the measured temperatures were analyzed. Effects of pins on the heat flux and heat transfer coefficient were discussed.

Experimental study of the influence of partially-filled foam metal on the performance of thermoelectric generator

WANG Shixue, LIANG Zhaojun, ZHAO Yulong, LI Yanzhe

2018, 35 (2): 233-239. DOI: 10.7523/j.issn.2095-6134.2018.02.013

Abstract ( 246 ) PDF (KB) ( 2 )

In recent years, semiconductor thermoelectric generation technology applied on waste heat recovery and recycle of high-temperature exhaust gas has gained wide attention. In this work we construct a testing system to simulate the vehicle exhaust, and study performance of the thermoelectric generator, that recovers the waste heat from automobile exhaust gas and converts it into electricity, by enhancing the heat transfer using foam metals with different hole densities filled in the core flow area.

Flow and heat transfer characteristics in a rectangular channel with vortex generators

TANG Linghong, ZENG Min

2018, 35 (2): 240-247. DOI: 10.7523/j.issn.2095-6134.2018.02.014

Abstract ( 261 ) PDF (KB) ( 2 )

In this study, effects of longitudinal vortex generator configurations (Case A-F) on the heat transfer and flow friction characteristics in a rectangular channel are investigated using numerical method. The results show that longitudinal vortex generator enhances the heat transfer performance, compared with the smooth channel. The field synergy principle analyses indicate that the intersection angles between velocity and temperature gradient of all longitudinal vortex generator configurations are smaller than that of smooth channel, and the comparison results show that at the same Reynolds number the smaller synergy angle the larger the Nusselt number is completely consistent with the field synergy principle. Comparisons of the performance evaluation parameter, JF factor, indicate that Case F has the best overall heat transfer performance and that Case F brings about more enhancement of heat transfer at a modest expense of the additional pressure. Therefore, Case F is a suitable configuration for enhancing the overall heat transfer performance for channels.

Thermal properties and phase transition properties of Cu/SiO₂ nanocomposites

LI Jing, LIAO Qiang

2018, 35 (2): 248-253. DOI: 10.7523/j.issn.2095-6134.2018.02.015

Abstract ( 283 ) PDF (KB) ( 1 )

Phase-change materials can be used to effectively realize the high efficiency and reasonable utilization of energy. We present a nanocomposite phase-change material, which is assembled mainly with filled nanoparticles and nanoporous substrates. Molecular dynamics method was used to simulate the phase-change behavior and thermal properties of metallic nanoparticles, nanoporous substrate, and composite. Thermal properties of metallic nanoparticles and nanoporous substrate were discussed under different sizes and conditions and compared with the thermal properties of composite materials. The research shows that the melting point of copper nanoparticles increases gradually with size and it is lower than that of bulk copper. Meanwhile, the heat capacity of copper nanoparticles is higher than that of bulk copper. Nanoporous SiO₂ substrate has no fixed melting point but has a large span of the melting zone, and its heat capacity increases with size or temperature and is significantly smaller than that of bulk SiO₂. The results show that the melting points of Cu/SiO₂ composites are higher than those of Cu nanoparticles and substrate, which means that composites enhance the structural stability. Meanwhile, the filled Cu nanoparticles effectively improve the heat storage characteristics of the nanoporous substrate.

Experimental investigation of lithium-ion power battery liquid cooling

AN Zhoujian, JIA Li, YANG Chengliang, DANG Chao, XU Mingchen

2018, 35 (2): 254-260. DOI: 10.7523/j.issn.2095-6134.2018.02.016

Abstract ( 576 ) PDF (KB) ( 5 )

A battery liquid cooling system which uses new electronic cooling fluid NOVEC 7000 as the working medium was proposed and some experimental investigation was carried out. The results showed that this system had excellent cooling effect. Temperature variation showed different regularities when the battery was discharged at different rates due to the different heat generation mechanisms. The effect of temperature on battery was bidirectional. Although the battery thermal management system effectively decreased the battery temperature and improved the thermal safety, the electrochemical performance declined as well. The maximum temperature of battery surface was effectively reduced with the increase in mass flow rate, but parasitic power resulting from the increase in mass flow rate, such as pump power consumption, should be considered. During cyclic charging/discharging, because of the boiling phenomenon, the maximum temperature of battery surface could be stably maintained between 34℃ and 36℃ when NOVEC 7000 was used as working medium.However, the temperature kept rising tendency while glycol was used as cooling medium. So, designing a battery thermal management system, based on flow boiling in mini/micro-channel, will effectively improve the thermal safety of batteries as well as the economy.

Influences of radiation temperature on convection of space floating zone under rotating magnetic field

ZOU Yong, ZHU Guiping, LI Lai, HUANG Hulin

2018, 35 (2): 261-269. DOI: 10.7523/j.issn.2095-6134.2018.02.017

Abstract ( 394 ) PDF (KB) ( 8 )

Through numerical simulation on a full floating-zone, the characteristics of thermocapillary convection in the melt are studied at different radiation heating temperatures under the rotating magnetic fields (RMF). The Lorentz force induced by the applied RMF under 1mT with 50Hz is not sufficient to effectively control the thermocapillary flow. In this case, the thermocapillary flow presents a rotating oscillatory three-dimensional convection with an oscillatory frequency decreasing with radiation temperature and varying linearly with Ma number. The temperature field in the melt has a 2-D steady axisymmetric distribution which is mainly determined by the diffusion effect when the Ma number is relatively small. However, at the relatively large Ma number, the temperature of the melt is influenced by flow and exhibits periodic oscillation with the same frequency of melt convection. By fixing RMF frequency at 50Hz and increasing the magnetic field intensity, the flow in melt turns into a quasi-2D rotating axisymmetric flow from a 3D periodic oscillatory convection. Accordingly the thermocapillary convection presents a mirror-symmetry structure about the middle plane. Both the temperature and velocity fluctuation in the melts with Ma=21.8,32.9,and 43.7 are effectively suppressed under 2, 3, and 5mT RMFs, respectively.

Ultrathin planar solar absorbers using monolayer two-dimensional materials

WANG Lin, LIU Dong, LI Qiang

2018, 35 (2): 270-274. DOI: 10.7523/j.issn.2095-6134.2018.02.018

Abstract ( 416 ) PDF (KB) ( 15 )

Monolayer two-dimensional (2D) materials hold promise for solar photovoltaics. This work investigated whether the 100% absorption could be achieved by 2D material solar absorbers with simple planar structure. The absorber was designed to consist of a 2D material film on top of a transparent layer coated on metallic substrate. The two-dimensional condition for perfect absorption can be satisfied by adjusting the transparent layer thickness and the incident angle. The results for the MoS₂ and graphene absorbers show that there always exist a pair of transparent layer thickness value and incident angle value at which these absorbers achieve the 100% absorption. In addition, these absorbers can be easily fabricated, and thus they pave the way to efficient 2D material photovoltaic devices.

Condensation heat transfer characteristics of steam with CO₂

GE Minghui, YU Ranran, ZHAO Jun, LIU Liansheng

2018, 35 (2): 275-279. DOI: 10.7523/j.issn.2095-6134.2018.02.019

Abstract ( 280 ) PDF (KB) ( 8 )

Based on the double boundary layer model, this work established a laminar condensation heat transfer model of steam with CO₂ on a vertical plate. The condensation heat transfer performance is deteriorated greatly due to the presence of CO₂. At a certain concentration of CO₂, with the increase of surface sub-cooling, the heat flux increases, the heat transfer coefficient decreases, and the interface temperature decreases almost linearly. With the increase of CO₂ concentration, the heat transfer coefficient decreases rapidly while the interface temperature increases gradually. In addition, the presence of CO₂ results in the formation of a layer of gas film outside the liquid film. With the increase of surface sub-cooling, the thickness of liquid film increases and the thickness of gas film decreases. Hoowever the thickness of the gas film is one order of magnitude larger than that of the liquid film. With the increase of CO₂ concentration, the thicknesses of liquid film and gas film both increase. However, the thermal resistance ratio of gas film to liquid film increases gradually, and the gas thermal resistance becomes dominant at high concentrations of CO₂.

Numerical investigation on heat transfer of supercritical CO₂ in rolling motion

ZHAO Zhenxing, LIN Yuansheng, ZHANG Kelong, LIU Zhouyang

2018, 35 (2): 280-288. DOI: 10.7523/j.issn.2095-6134.2018.02.020

Abstract ( 347 ) PDF (KB) ( 3 )

The numerical calculations with and without rolling motion are carried out to investigate the effects of rolling motion on flow and heat transfer of supercritical CO₂. It is concluded that the effect of rolling motion on the supercritical CO₂ is much stronger than that on conventional single-phase fluid. The rolling motion causes the periodic oscillation of the local heat transfer coefficient and suppresses the whole heat transfer deterioration. As the supercritical CO₂ temperature increases, the influence of rolling motion on the heat transfer decreases markedly. The heat transfer deterioration phenomenon gradually weakens as the rolling period decreases or rolling amplitude increases.

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