Numerical Analysis on Charging Performance of the Macro-Encapsulating Combined Sensible-Latent Heat Storage System with Structural Parameters

For combined sensible-latent heat storage system(CSLHS)(termed as the hybrid configuration),macro encapsulation can effectively solve the leakage problem of PCMs.However,due to the poor thermal conductivity of PCMs,the charging performance of the hybrid configuration slightly increases compared to the solid structure(with only sensible materials).Meanwhile,the natural convection in the PCMs zone could improve the charging performance.So,how to improve natural convection intensity is a key issue for the CSLHS by macro encapsulating.It is found that adding fins can significantly enhance natural convection and accelerate the melting of PCM.In this paper,we proposed the hybrid configuration with fins built-in by macro encapsulation,and analyzed its charging performance with different fin structural parameters in the PCM zone by CFD simulation.In the case,the sensible heat storage material is high-temperature concrete and the PCM is a low-melting-point mixed molten salt.We analyzed the effects of fin number,fin length and fin thickness on the charging performance of the hybrid configuration respectively.From the result,the charging performance increases with the fin number,but the increase rate gradually decreases.When the fin number is 6,the charging performance increases by 20.18%compared to the situation without fin.The charging performance increases gradually with the fin length.Compared with the hybrid configuration without fin,for each 10 mm increase in fin length,its charging performances increase by 4.09%,5.26%,7.02%,8.77%,11.70%,and 15.79%,respectively.Different from number and length of fins,the effect of thickness on the charging performance is very small.When the fin thickness increased from 1 mm to 4 mm,the charging performance only increased by 2.3%.It indicates that the main reason for the improving the charging performance is to increase the natural convection intensity by dividing the PCM zone through fins.These results show that the charging performance of the CSLHS with macro encapsulation can be improved by optimizing fin structural parameters.

Numerical Simulation of Charging Performance of Combined Sensible-Latent Heat Storage System with a Macro-Encapsulation Method

In recent years,heat storage system combining sensible and latent heat materials has received more and more attentions.In this paper,we proposed the hybrid configuration with a macro-encapsulation,and analyzed its charging performance with different influencing factors by CFD simulation.In the case,the sensible heat storage materials are magnesia brick or HT concrete and the phase change materials(PCMs)are mixed molten salts.Firstly,we analyzed the heat transfer characteristics of the hybrid configuration in charging process.Then,we analyzed the effect of heating power on charging performance.The maximum temperature of the heating surface shall not exceed 500℃as the constraint condition,the heat storage capacity increases at first and then decreases with the heating power.Then,we compared the charging performance of different solid structure and the hybrid configurations.Whether magnesia brick or HT concrete,the charging performance of the solid structure is better than that of the hybrid configuration,because the thermal conductivity of the molten salt is significantly lower than that of the two sensible heat storage materials.Then,we compared the charging performance of different molten salts.The hybrid configuration with lower melting point molten salt has better performance because of more intensity natural convection.Finally,we analyzed the charging performance of the hybrid configuration used the composite phase change material(CPCM)with high thermal conductivity and specific heat.From the result,the charging performance increases by 22.5%compared with the solid structure.These results indicate that the hybrid configuration with the macro-encapsulation method is a potential form of thermal energy storage,but it needs to be further optimized.

Microstructures and Properties of Honeycomb Sulfur/carbon Black/MoS_(2) Composites

Microstructure and property of sulfur/carbon black composites prepared by ball milling were studied.Sulfur/carbon black composites were obtained by melting the mixture of sulfur and carbon black in 155℃and dispersing evenly in carbon black after hydrothermal reaction.Thus,its conductive properties were improved.Moreover,microstructure and property of honeycomb sulfur/carbon black/MoS_(2) prepared by hydrothermal method as a cathode material for lithium-sulfur batteries were studied.The initial discharge specific capacity of the material at 0.2 A/g current density is 838.495 mA·h/g,and the 55.14%after 100 weeks of cycling.It is indicated that MoS_(2) can not only combine with polysulfides through electrostatic action or the action of chemical bonds,but also honeycomb porous structure.MoS_(2) can fix polysulfides groups and prevent their shuttle.Therefore,the cycling performance of the battery is effectively improved.

Effect of Residual Charge Carrier on the Performance of a Graphene Field Effect Transistor

The temperature-dependent effect of residual charge carrier （no）, at the Dirac point, on mobility is studied. We fabricate and characterize a graphene field effect transistor （GFET） using 7nm TiO2 as the top-gate dielectric. The temperature-dependent gate voltage-drain current and room temperature gate capacitance are measured to extract the carrier mobility and to estimate the quantum capacitance of the GFET. The device shows the mobility value of gOO cm^2 /V.s at room temperature and it decreases to 45 cm^2 /V.s for 20 K due to the increase of n0. These results indicate that the phonon scattering is not the dominant process for the unevenness dielectric layer while the coulomb scattering by charged impurities degrades the device characteristically at low temperature.

Impact of Band-Engineering to Performance of High-k Multilayer Based Charge Trapping Memory

Impact of band-engineering to the performance of charge trapping memory with HfO2/Ta2O5/HfO2 （HTH） as the charge trapping layer is investigated. Compared with devices with the same total HfO2 thickness, structures with Ta2O5 closer to substrates show larger program/erase window, because the 2nd HfO2 （next to blocking oxide） serving as part of blocking oxide reduces the current tunneling out of/in the charge trapping layer during program and erase. Moreover, trapped charge centroid is modulated and contributed more to the fiat-band voltage shift. Further experiments prove that devices with a thicker 2nd HfO2 layer exhibit larger saturate fiat-band shift in both program and erase operation. The optimized device achieves a 7 V memory window and good reliability characteristics.

Penetration performance of W/Cu double-layer shaped charge liners

Two kinds of W/Cu double-layer shaped charge liner（SCL） were prepared by chemical vapor deposition（CVD） combined with electroforming technique： A SCL with W inner layer and Cu outer layer, B SCL with Cu inner layer and W outer layer. The penetration properties of A and B SCLs were researched. The results show that the two SCLs can form continuous jet and the tip velocities of A and B jets are 7.4 and 6.3 km s^（-1）, respectively. The kinetic energy density（5.3 9 1011 J m-3） of A jet tip increases by 194.4 %compared with that（1.8 9 1011 J m-3） of B jet tip. B jet,however, exhibits deeper penetration depth at the same experimental conditions. The chemical component and microstructure of the area nearby the ballistic perforation were researched. Component analysis shows that both the jets are formed only from inner layer metal. Microstructure analysis shows that martensite and intermetallic form around ballistic perforation penetrated by A SCL due to the intensive interaction between W jet and steel target. The two kinds of newly formed ultrahard phases also hinder the jet from penetrating target further. As a result of relatively alleviative interaction between Cu jet and target, only solid solution rather than ultrahard phases forms around ballistic perforation penetrated by B SCL.

Charge transport performance of high resistivity CdZnTe crystals doped with In/Al

To evaluate the charge transport properties of as-grown high resistivity CdZnTe crystals doped with In/Al, the α particle spectroscopic response was measured using an un-collimated 241Am （5.48 MeV） radioactive source at room temperature. The electron mobility lifetime products （μτ）e of the CdZnTe crystals were predicted by fitting plots of photo-peak position versus electrical field strength using the single carrier Hecht equation. A TOF technique was employed to evaluate the electron mobility for CdZnTe crystals. The mobility was obtained by fitting the electron drift velocities as a function of the electrical field strengths, where the drift velocities were achieved by analyzing the rise-time distributions of the voltage pulses formed by a preamplifier. A fabricated CdZnTe planar detector based on a low In concentration doped CdZnTe crystal with （μτ）e = 2.3 × 10？3 cm2/V and μe =1000 cm2/（V·s）, respectively, exhibits an excellent γ-ray spectral resolution of 6.4% （FWHM = 3.8 keV） for an un-collimated 241Am @ 59.54 keV isotope.

Enhanced rate capability and mitigated capacity decay of ultrahigh-nickel cobalt-free LiNi_(0.9)Mn_(0.1)O_(2) cathode at high-voltage by selective tungsten substitution

Owing to the further requirement for electric vehicle market, it is appropriate to lower the cost and improve the energy density of lithium-ion batteries by adopting the Co-free and Ni-rich layered cathodes.However, their practical application is severely limited by structural instability and slow kinetics. Herein,ultrahigh-nickel cobalt-free LiNi_(0.9)Mn_(0.1)O_(2) cathode is elaborate designed via in-situ trace substitution of tungsten by a wet co-precipitation method following by high-temperature sintering. It is revealed that the in-situ doping strategy of high valence W^(6+) can effectively improve the structure stability by reducing irreversible phase transition and suppressing the formation of microcracks. Moreover, the transformed fine particles determined by W-doping can facilitate the kinetic characteristics by shortening Li^(+) diffusion paths. As expected, 0.3 mol% W-doped LiNi_(0.9)Mn_(0.1)O_(2) cathode exhibits a high specific capacity of 143.5 mAh/g after 200 cycles at high rate of 5 C in the wide potential range of 2.8-4.5 V, representing a potential next-generation cathode with low-cost, high energy-density and fast-charging capabilities.

High energy storage properties in Ca_(0.7)La_(0.2)TiO_(3)-modified NaNbO_(3)-based lead-free antiferroelectric ceramics

In this work,(1−x)(0.92NaNbO_(3)-0.08BaTiO_(3))-xCa_(0.7)La_(0.2)TiO_(3)(NNBT-xCLT)ceramics were successfully designed and pre­pared by the solid-state reaction method.Investigations on the structure,dielectric,and energy storage properties were performed.The NNBT-0.25CLT ceramic with orthorhombic phase at room temperature was found to exhibit extremely small grain size and compacted microstructure.A large Wrec of 3.1 J/cm^(3) and a highηof 91.5%under the electric field of 360 kV/cm were achieved simultaneously in the sample.In addition,the energy storage performance of the sample exhibits thermal stability over the tem­perature range of 25-140°C and the frequency range of 5-500 Hz.The charge and discharge tests reveal that the ceramic shows a large current density CD of 965 A/cm2 and power density PD of 154 MW/cm^(3).This work demonstrates that the NNBT-0.25CLT ceramic is a prospective energy storage material for potential application in the field of pulsed power devices.