Structural Evolution and Phase Change Properties of C-Doped Ge_2Sb_2Te_5 Films During Heating in Air

We elucidate the importance of a capping layer on the structural evolution and phase change properties of carbondoped Ge2 Sb2 Te5（C-GST） films during heating in air. Both the C-GST films without and with a thin SiO2 capping layer（C-GST and C-GST/SiO2） are deposited for comparison. Large differences are observed between C-GST and C-GST/SiO2 films in resistance-temperature, x-ray diffraction, x-ray photoelectron spectroscopy,Raman spectra, data retention capability and optical band gap measurements. In the C-GST film, resistancetemperature measurement reveals an unusual smooth decrease in resistance above 110℃ during heating. Xray diffraction result has excluded the possibility of phase change in the C-GST film below 170℃. The x-ray photoelectron spectroscopy experimental result reveals the evolution of Te chemical valence because of the carbon oxidation during heating. Raman spectra further demonstrate that phase changes from an amorphous state to the hexagonal state occur directly during heating in the C-GST film. The quite smooth decrease in resistance is believed to be related with the formation of Te-rich GeTe4-n Gen（n = 0, 1） units above 110℃ in the C-GST film. The oxidation of carbon is harmful to the C-GST phase change properties.

Thermal properties in phase change wallboard room based on air conditioning cold storage

By comparing the thermal performance parameters of an ordinary wall room with a phase change wall (PCW) room,the effect of phase change wallboard on the fluctuation of temperature in air-conditioning room in summer was studied. And PCW room and an ordinary wall room,which are cooled by air-conditioner,were built up. Differential scanning calorimetry (DSC) was used to test the temperature field and heat flow fluctuation in these rooms. Through analyzing the data tested,it is found that the mean temperature of PCW is lower than that of ordinary wall room by 1-2 ℃,and PCW can lower the heat flow by 4.6 W/m2. Combining phase change material to building envelope can lower the indoor temperature,make the room thermal comfortable,and cut down the turn-on-and-off frequency of air-conditioner,the primary investment and operating costs. It alleviates urgent need of the electric power. Building envelope which contains phase change wallboard can improve the indoor thermal environment,and decrease energy consumption in buildings. Phase change wallboard can make impressive effect on energy efficiency of buildings.

Localisation and phase transition of acoustic waves in a soft medium containing air bubbles

We study via numerical experiments the localisation property of an acoustic wave in a viscoelastic soft medium containing randomly-distributed air bubbles. The behaviours of the oscillation phases of bubbles are particularly investigated in various cases for distinguishing efficiently the acoustic localisation from the effects of acoustic absorption caused by the viscosity of medium. The numerical results reveal the phenomenon of ＇phase transition＇ characterized by an unusual collective oscillation of bubbles, which is an effective criterion to unambiguously identify the acoustic localisation in the presence of viscosity. Within the localisation region, the phenomenon of phase transition persists, and a remarkable decrease in the fluctuation of the oscillation phases of bubbles is observed. The localisation phenomenon will be impaired by the enhancement of the viscosity factors, and the extent to which the acoustic wave is localised may be determined by appropriately analyzing the values of the oscillation phases or the amount of reduction of the phase fluctuation. The results are particularly significant for the practical experiments in an attempt to observe the acoustic localisation in such a medium, which is in general subjected to the interference of the great ambiguity resulting from the effect of acoustic absorption.

Time Sequential and Phase-resolved Measurement and Analysis of Corona Discharge in Air and Streamer Discharge in Insulating Liquid

Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.

Modelling of a Two-Phase Thermosyphon Loop for Passive Air-Conditioning of a House in Hot and Dry Climate Countries

The two-phase thermosyphon loop is an efficient solution for space cooling. This paper presents the simulation results of numerical studies on the heat transfer and thermal performance of a two-phase thermosiphon loop for passive air-conditioning of a house. The fluid considered in this study is methanol, which is compatible with copper and is environmentally friendly. These numerical results show that the temperature at the evaporator wall drops from 23°C to 13°C and increases at the condenser. The solar flux density has a strong influence on the condenser temperature. The mass flow rates and masses at the evaporator and condenser increase with temperature. The variation of evaporating and condensing temperature affects the performance of the system. For a constant evaporating and condensing temperature of 2°C and 29°C, the COP is 0.77 and 0.84 respectively. With these results, the use of the two-phase thermosyphon loop in air conditioning is possible to obtain a thermal comfort of the occupants acceptable by the standards but with a large exchange surface of the evaporator.

Thermo-hydro-mechanical-air coupling finite element method and its application to multi-phase problems

In this paper, a finite element method （FEM）-based multi-phase problem based on a newly proposed thermal elastoplastic constitutive model for saturated/unsaturated geomaterial is discussed. A program of FEM named as SOFT, adopting unified field equations for thermo-hydro-mechanical-air （THMA） behavior of geomaterial and using finite element-finite difference （FE-FD） scheme for so/l-water-air three-phase coupling problem, is used in the numerical simulation. As an application of the newly proposed numerical method, two engineering problems, one for slope failure in unsaturated model ground and another for in situ heating test related to deep geological repository of high-level radioactive waste （HLRW）, are simulated. The model tests on slope failure in unsaturated Shirasu ground, carried out by Kitamura et al. （2007）, is simulated in the framework of soil-water-air three-phase coupling under the condition of constant temperature. While the in situ heating test reported by Munoz （2006） is simulated in the same framework under the conditions of variable temperature hut constant air pressure.

快掘面风流动态调控参数与压抽比对粉尘运移的影响及降尘分析

随着矿山快掘设备的逐渐引进,快掘面粉尘污染问题愈加严重。为有效减少快掘面生产过程中的粉尘污染,设计出风流动态调控降尘净化系统,通过调节风流的状态并设计了不同工况下的风流调控方案,以降低司机处粉尘浓度与粉尘的扩散距离。以陕西某矿快掘面为例,建立了风流—粉尘耦合场有限元模型,并对模型进行了井下验证;分析了风流动态调控降尘净化系统中出风口偏角、出风口缩放口径、出风口距端头距离及风量压抽比4个参数对风流与粉尘场的影响规律;设计正交试验分析了各参数与司机处粉尘浓度与粉尘扩散距离之间的关联性,确定了最佳调控净化方案。结果表明:各参数对司机处粉尘浓度与粉尘扩散距离影响程度的显著性排序由大到小依次为风量压抽比、出风口偏角、出风口距端头距离、出风口缩放口径。确定的最佳调控净化方案为出风口距离端头10 m、出风口偏角20°、出风口缩放口径1.0 m及风量压抽比1。设计搭建试验平台进行了准确性及净化效果测试验证,模拟值与试验值的平均误差小于8.91%,净化后司机处粉尘浓度由327.22 mg/m^(3)降低至156.47 mg/m^(3),降低了52.18%,粉尘扩散距离由39.74 m缩短至25.91 m,缩短了34.80%,有效改善了快掘面的空气环境。

Numerical Method for Heat and Mass Transfer in Air Washer——3.Two-phase Flow in Eliminator

Numerical simulation method is applied in the study oftwo - phase flow dynamics in the eliminator of air wash-er. The carrier phase (air) is treated in Eulerian frame,the water droplets are tracked in the Lagrangian frame.A three - dimensional unsteady two - phase flow model isdeveloped. With the help of FLUENT software, air-stream velocity field and water droplets trajectories havebeen illustrated when their mixture passing through tra-ditional folded eliminator. The result of the simulationcan be used to investigate the mechanism of

Experimental and numerical simulation of air-water two-phase flow in the rod bundle with grid spacer

Experimental and numerical simulation were carried out on vertically upward air-water two-phase flow in the rod bundle with grid spacer. The related numerical simulation has been performed by using the Computational Fluid Dynamics code-CFX4.2, in which lateral interfacial effects based on a two-fluid model are accounted for. This model has been used to evaluate the velocity fields of gas and liquid phases, as well as phase distribution between elements in rod bundle by simulating 1/4 zone of experimental model, and mixing vanes of spacer in this area. Fur- thermore, this model has been used to predict the effects of spacer on flow and pressure drop along the rod bundle. The calculation results show that the mixing vane has significant influence on axial and lateral velocity. In order to obtain some experimental data to verify the numerical solutions, a series of tests, using a specially designed 3×3 rod bundle test section with AFA-2G structure spacer have been performed. An optical probe was used to measure local void fractions. At the same time, the pressure loss has been measured. A comparison between the calculated void pro- file and pressure loss and the measured results shows that the predicted void profiles are consistent at low gas appar- ent velocity. This research shows that the code CFX4.2 can be used to describe the 3-D air-water two-phase flow in the rod bundle channel with grid spacer.

Research on the Phase Change Solar Energy Fresh Air Thermal Storage System

In this article, a new kind of solar fresh air system is designed in order to realize the improvement of thermal efficiency by the integrated application of the PCMs and heat pipe technology. Under the adequate sunshine condition, the fresh air is directly delivered into the indoor environment after being heated by the solar collector. When the sun radiation is reduced, the heated air temperature can not satisfy the need of supply of air temperature.The main heat source is changed to phase change heat storage equipment instead of solar energy. The system adopt heat pipe for a high-efficiency and isothermal heat transfer which recover the shortcomings of PCMs such as： low coefficient of thermal conductivity and poor thermal efficiency. This article establishes the physical model of phase change solar energy fresh air thermal storage system and creates the mathematical model of its unsteady heat transfer to simulate and analyse the operation process by using Fluent software. The results of the study show that, compared to normal fresh air system, the phase change solar energy fresh air thermal storage system has a significant improvement in energy saving and indoor comfort level and will play an important role in the energy sustainable development.

轴径向静态偏心故障下外转子永磁发电机电磁转矩特性分析

对外转子永磁发电机轴径向静态偏心故障下的电磁转矩特性进行了理论解析、仿真计算和实验验证。首先,在考虑齿槽效应影响条件下,引入磁导修正系数ε(θ),推导出轴径向静态偏心前后气隙磁密表达式,并考虑绕组分布情况,构建一种新型的永磁发电机轴径向静态偏心故障下相电流数学模型,在此基础上得到轴径向偏心下电磁转矩解析表达式。其次,通过有限元仿真计算得到外转子永磁发电机轴径向静态偏心下的电磁转矩波动特性。最后,在一台外转子永磁发电机上通过故障模拟实验实例印证了解析分析和仿真计算结果。结果表明:相较于正常情况,径向偏心时,电磁转矩以直流、二倍频、四倍频成分为主,随着偏心程度的加剧,电磁转矩的直流、二倍频、四倍频成分幅值将随着增大;轴向偏心时,电磁转矩谐波成分不变,随着偏心程度的加剧,各谐波成分幅值将随着减小。对外转子永磁发电机气隙偏心故障分析的一个重要补充,对此类问题的现场检测和鉴定具有参考价值。

喷嘴位置对轴承腔内油气润滑两相流的影响

基于气液两相流理论,采用多重坐标系法构建角接触球轴承数值计算模型,分析不同喷嘴位置和转速下轴承腔内油相体积分数、保持架表面及轴承内外圈的油气分布特性。结果表明:在轴承低转速下,正面供油时轴承腔内油相体积分数及其周向分布的波动大于背面供油;正面供油时保持架下表面会产生润滑油的积聚,造成润滑油无法及时通过出口排出,而背面供油时润滑油在保持架表面的油相分布更均匀;正面供油时内圈左面油相体积分数较高,外圈油相分布变化较大,而背面供油时内圈右面、中间面及外圈中间面油相体积分数较高。不同转速下喷嘴位置对腔内油相分布的影响也不同,低转速下正面供油时腔内油相体积分数更高,高转速下喷嘴位置对轴承腔内油相分布的影响较小,润滑油在轴承腔内分布较为均匀,保持架下侧未见明显的润滑油积聚。

新型迷你通道-相变热沉实验研究

电子元件的集成化、微型化等特点加剧了芯片的热问题,基于相变材料的被动式冷却技术已无法满足功率波动的高功率电子设备的需求。本文将相变技术与主动冷却技术相结合,提出了一种用于风冷散热的新型迷你通道-相变热沉结构。该结构改善了相变材料导热性能差的问题,也解决了相变材料熔化后泄漏的问题。通过实验测试了不同热流密度、不同风速对其热控性能的影响,总结了热沉的蓄放热特性,并与未填充相变材料热沉的热控性能进行了对比。实验中热流密度变化范围为1.81~3.47 W/cm^(2),风速变化范围为0~4 m/s。研究表明:热流密度的增大和风速的降低均会导致热沉温控时间的缩短。2 m/s风速足以满足热流密度小于2.91 W/cm^(2)的芯片散热需求,4 m/s风速可以在热流密度为3.47 W/cm^(2)的情况下将热沉底面温度维持在70℃。与未填充相变材料热沉相比,本研究提出的热沉可以起到延长温控时长,降低稳态温度的作用。此外,风扇的开启可以有效缩短热沉的冷却时间,对于间歇性工作的电子设备具有重要的应用意义。研究结果可为迷你通道-相变热沉在实践中的应用提供参考依据。

角接触球轴承内圈织构设计及对油气润滑两相流的影响

针对角接触球轴承油气润滑中内圈润滑油含量少和保持性差的问题,提出在轴承内圈滚道设计圆凹坑形表面织构的润滑增效方法。基于气液两相流模型和多重参考系方法,建立内圈织构化角接触球轴承腔内油气两相流数值分析模型,分析内圈织构对轴承油气两相流动及润滑增效的影响。结果表明:织构化轴承可以显著提高润滑油在内圈的保持量,同时改善轴承腔内润滑油分布不均的状况;在微织构附近油气两相流动更不规则,所产生的压力梯度和速度梯度有利于提高气液两相膜的承载力;随着轴承转速的升高,内圈织构润滑增效效果相对减弱;随着供油量的增加,内圈织构润滑增效效果更加显著。

不同倾斜度下管道充水特性分析

针对管道充放水周期较长的问题,在对比模拟结果与试验数据吻合度的基础上,建立5种不同倾斜角度的管道三维模型,仿真不同倾斜角度下管道充水过程,分析其内部流速、压力和气液两相分布变化情况。结果表明,管道倾斜度小于30°时,水流流态稳定,流线均匀,管内水位均匀上升,平均充水流速1.3 m/s;随着倾斜度增加,流速越来越快,气液两相混合流动现象越来越明显,当倾斜角度为60°时,存在气体拥塞管道现象。综合对比,建议管道在倾斜度小于30°时可以适当增加充水速度,缩短充水周期。

太阳能空气源热泵耦合相变蓄热器供热系统模拟研究

目的为提高可再生能源利用率,研究太阳能空气源热泵耦合相变蓄热器供热系统实际性能,建立适合夏热冬冷地区民用住宅的节能供热系统。方法利用TRNSYS软件建立太阳能空气源热泵耦合相变蓄热器供热系统模型,并与太阳能空气源热泵供热系统进行对比分析,对两个系统从制热量、耗电量、能效比以及室内人体热舒适度四个方面进行模拟分析,使用PMV-PPD评价方法对两个系统的室内热舒适度进行评价。结果耦合相变蓄热器的供热系统耗电量低于无相变供热系统,节能率提高了13.29%;耦合相变蓄热器的供热系统平均能效比为3.5,太阳能空气源热泵供热系统的平均能效比为3.32,提高了5.14%;耦合供热系统可以为人体提供I级室内热环境水平的热舒适度,无相变供热系统只能为人体提供II级。结论太阳能空气源热泵耦合相变蓄热器供热系统节能性更好,系统能效更高,提高了可再生能源利用率,并且耦合供热系统在热舒适性方面优于无相变供热系统。

相变储热技术在空气源热泵供暖中的应用研究现状

空气源热泵技术因具有节能、环保、高效等优点,在我国建筑供暖领域得到了广泛应用。文章分析了空气源热泵系统在供暖过程中存在的问题,介绍了利用相变储热技术优化空气源热泵运行性能的基本方式及原理。通过分析相变材料自身热物性以及相变储热单元在系统中的应用,从材料及系统两方面简述了相变储热技术在空气源热泵供暖中的研究现状及进展。最后,得出结论并针对相变储热技术在空气源热泵供暖中的应用难点,对未来发展进行了展望。

新型储能技术进展与挑战Ⅱ:物理储能与储热技术

新型储能技术日益成为中国建设新型能源体系和新型电力系统的关键技术,已成为中国经济发展的新动能,将在促进可再生能源消纳、实现能源体系转型、提高能源利用效率、减少环境污染等方面发挥重要作用,相关技术研究也在快速发展。开展了该领域的系列评价性综述工作,分为电化学储能技术、物理储能与储热技术、储能集成与规划3个部分,对各类新型储能技术的应用领域、最新研究进展及局限性等问题进行了全面系统的对比分析,并进一步探讨了储能集成、安全、规划调度等储能系统相关领域面临的挑战及发展趋势。第2部分为物理储能与储热技术,重点对物理储能与储热技术中的压缩空气储能、飞轮储能、重力储能、相变储热、热化学储热和卡诺电池技术与工程的相关成果进行了综合分析与讨论。总体而言,物理储能和储热技术大多具有使用寿命长、安全性高的特点,且在能量转化过程中自身多具有转动惯量,属于电网支撑型的储能技术,可满足从大规模长时储能到高功率快速响应的不同需求。在新兴的物理储能和储热技术中,重力储能和卡诺电池的相关技术显示出良好的发展前景。

侧深施肥装置三通管气固两相流仿真与试验

为探究气吹式侧深施肥装置三通管不同结构特征对气流和肥料颗粒运动的影响,通过理论分析,设计气流入口与出口轴线垂直的a型三通管、气流入口与出口轴线呈45°夹角的b型三通管、气流入口与出口同轴的c型三通管。在三通管内径为28 mm、通入气流速度为16.4 m/s、肥料颗粒流量为20 g/s的条件下,采用CFD-EDM耦合方式对不同管道内气流、压力、颗粒运动状态进行仿真分析。结果表明:气流经a、b、c三种类型三通管产生不同的流动效果,进而影响肥料颗粒运动特性,颗粒最大运动速度分别为1.99 m/s、2.94 m/s、2.07 m/s,期间颗粒产生最大碰撞力分别为0.05 N、0.13 N、0.34 N。通过验证试验对比表明,采用b型管侧深施肥装置排肥稳定性变异系数为0.81,肥料破损率为0.72%,施肥过程中无肥料堵塞。

立构复合化聚乳酸纳纤膜的制备及高效滤除PM_(2.5)性能

聚乳酸(PLA)纳米纤维在环境友好型纤维过滤材料领域有良好的应用前景,但受制于其本征螺旋分子链构象和低介电常数的不足,导致其驻极性能差、过滤性能(过滤效率及压降)易衰减以及有效服役周期短.本文将高旋光性的聚L-乳酸(PLLA)和聚D-乳酸(PDLA)溶液共混,并通过静电纺丝过程的高压静电场诱导C=O基团加速取向极化,形成高电活性的立构复合晶体(SCs),显著提高聚乳酸纳纤膜的表面电位、介电常数及驻极效果等电活性特征,增大纤维表面静电斥力,促进PLA纳纤膜(PLA NFMs)的纤维细化,从而使其压降大幅降低(85 L/min,209.2 Pa),过滤PM_(2.5)效率显著提高至96.32%(纯PLLA对比样为72.44%).更重要的是,立构复合化PLA纳纤膜(SC-PLA NFMs)的过滤性能受气体流量变化影响较小(10~85 L/min),当气流增大时,过滤效率的衰减远远低于纯PLLA,在高气流下的稳定性使其能更好地满足在空气过滤领域的实际应用需求.此外,提高PLA纳纤膜电活性可显著增强摩擦生电输出性能和呼吸振动激发电信号,为基于人体呼吸的生理特征监测奠定理论基础.本文研究结果为扩大PLA材料在高性能呼吸防护领域和智能健康监测领域的应用提供了新颖的结构设计策略和可借鉴的解决方案.