Novel and durable composite phase change thermal energy storage materials with controllable melting temperature

The development of high temperature phase change materials(PCMs)with great comprehensive per-formance is significant in the future thermal energy storage system.In this study,novel and durable Al-Si/Al2O3-AlN composite PCMs with controllable melting temperature were successfully synthesized by using pristine Al powder as raw material and tetraethyl orthosilicate as SiO2 source.The Al2O3 shell and Al-Si alloy were in-situ produced via the substitution reaction between molten Al and SiO2.Impor-tantly,the crack caused by the incomplete encapsulation of the Al2O3 shell could repair itself by the nitridation reaction of internal molten Al and thereby forming a highly dense Al2O3-AlN composite shell.The produced dense Al2O3-AlN composite shell could significantly improve the thermal cycling stability of composite PCMs,and thus,the thermal storage density decrease of the Al-Si/Al2O3-AlN(59.8 J/g to 77.7 J/g)was far less than that of the Al-Si/Al2O3(118.5 J/g)after 3000 thermal cycles.Moreover,the syn-thesized Al-Si/Al2O3-AlN still exhibited a controllable melting temperature(571.5-637.9℃),relatively high thermal storage density(105.6-150.7 J/g),great dimensional stability and structural stability after 3000 thermal cycles.Hence,the synthesized Al-Si/Al2O3-AlN composite PCMs,as promising preferential thermal energy storage materials,can be stably used in the energy utilization efficiency improvement of various systems for more than 6 years.     

潜热储能石膏基建筑材料的制备及其储(放)热行为研究

以膨胀石墨为吸附介质,硬脂酸丁酯为吸附对象,可以制得有机/无机复合相变材料,将这种复合材料掺入石膏中制备潜热储能石膏建材.DSC的测试结果显示,复合相变材料的相变焓值与纯硬脂酸丁酯的相变焓值基本相当,体现了良好的热物理性能.考虑到浆体的和易性,复合相变材料在石膏试样中的掺量不宜超过5%.在石膏硬化浆体中,复合相变材料与石膏浆体间的界面具有一定的缺陷,但是对石膏试样的强度影响不大.温度循环试验显示,复合相变材料掺量5%的潜热储能石膏具有良好的储(放)热效果,这种特性将有助于增加环境温度波动的惰性,实现热量在不同时间上的迁移,从而在建筑节能领域中加以应用.     

一种适合潜热输送的高温相变石蜡乳状液的热性能

针对太阳能利用、余热利用、集中供暖等应用背景,采用差示扫描量热法(DSC)遴选了一种相变温度合适(相变峰值87℃)、相变潜热值较大(203.9J/g)的工业石蜡,并以此为相变材料,采用非离子型乳化剂及助乳剂复配的方法研制了3种浓度的石蜡乳状液高温潜热输送材料。测定了石蜡乳状液高温潜热输送材料的相变点、相变潜热等热物性,并研究了其蓄热特性。结果表明,该材料是一种在80～90℃之间存在相变的储、传热工质,在相变区间内的储、载热密度远大于水,是一种良好的潜热输送材料。     

铅纳米线熔化温度的尺寸效应研究

利用分子动力学的方法研究了Pb纳米线熔化温度的尺寸效应.研究表明,纳米线的熔化温度随着尺寸的减小而降低,纳米线的熔化过程从表面开始,并逐渐向中心趋近.纳米线在熔化过程中,温度也在逐渐升高,这不同于块体材料.Pb纳米线熔化温度的变化量与相同尺寸Pb纳米薄膜的变化量之比为2:1.另外,Pb纳米线的热力学稳定结构存在一个临界尺寸S(2nm＜S＜2.5nm),尺寸＜S,Pb纳米线的稳定结构是晶态,而＜S则为非晶态.     

氦-3的汽化热和熔解热

基于Clausius-Clapeyron方程、维里方程和最新开发的氦-3相平衡曲线方程计算了氦-3在平衡曲线上的两个重要性质:汽化热(0 K～3.315 7 K)和熔解热(0.001 K～35 K).计算结果覆盖的温度范围广,精度也满足工程应用的需求.     

NiTi合金热容的测定及传热的研究

使用调制式差示扫描量热器（MDSC）精确测定了Ni-Ti合金的比热容。研究了以不同的速度加热和冷却合金时相变点的变化,并用试验测定的热容值,计算了电流加热的NiTi合金丝的温度变化历程,这将为科学合理地计算加热时合金的温度场提供参考信息。     

水合无机盐相变潜热影响因素的研究

以水合无机盐的相变温度、潜热等数据为研究对象,利用归纳法对表中数据进行分析,证明阴、阳离子的性质、水合离子构型及键合方式、结晶水个数是影响相变潜热的主要因素;水合无机盐的中心离子只与水分子相连时,相变潜热与中心离子相关,结晶水平均相变潜热为7kJ·mol-1;中心离子同时与水分子、阴离子配位的混合水配合物,结晶水平均相变潜热为12kJ·mol-1;两类水合物摩尔潜热均与结晶水个数成正比.水合无机盐相变潜热的影响因素的研究对相变潜热值的预测、相变材料的筛选有重要意义.     

相变储热技术在太阳能热泵中的应用

在阐述相变储热的应用研究状况和分析其应用于太阳能热泵的必要性的基础上，重点介绍常用于太阳能热泵的常低温相变材料特点及相变储热装置，给出带储热器的太阳能热泵的运行模式，最后指出相变储热技术在太阳能热泵的应用领域应重点研究的内容。     

A transient (subsecond) technique for measuring heat of fusion of metals

A transient technique is described for measuring the heats of fusion of metals with melting temperatures above 1500 K. The specimen configuration consists of a strip of the metal under study sandwiched between two strips of another metal with a higher melting temperature. The basic method consists of rapidly heating the composite specimen by passing a subsecond-duration electrical current pulse through it and simultaneously measuring the radiance temperature of the containment metal surface, as well as the current through and voltage drop across the specimen. The melting of the metal under study is manifested by a plateau in the temperature versus time function for the containing metal surface. The time integral of the power absorbed by the specimen during melting yields the heat of fusion. Measurements on several tantalum-niobium-tantalum specimens yield a value of 31.5 kJ · mor^–1 for the heat of fusion of niobium, with an estimated maximum inaccuracy of ± 5%.     

Measurement of the heat of fusion of molybdenum by a microsecond-resolution transient technique

A microsecond-resolution pulse-heating technique was used for the measurement of heat of fusion of molybdenum. The method is based on rapid resistive self-heating of the specimen by a high-current pulse from a capacitor discharge system and measuring current through the specimen, voltage across the specimen, and radiance temperature of the specimen as functions of time. Melting of the specimen is manifested by a plateau in the temperature versus time function. The time integral of the power absorbed by the specimen during melting yields the heat of fusion. Measurements gave a value of 36.4 kJ · mol^–1 for the heat of fusion of molybdenum with an estimated maximum uncertainty of±6%.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.Formerly National Bureau of Standards     

-60℃低温冷库传热系数测量试验研究

简述对于低温冷库传热系数测量所采用的一般方法，采用稳态法对一低温试验冷库进行实验，然后通过非稳态积分法对试验数据进行验证。针对冷风机电机功率较大的特点，本实验采用变频器将电机功率调小，从而得出该低温试验冷库的传热系数，并与理论计算的数据进行对比，找出存在差异的原因。     

Thermophysical interpretation of the latent heat of vaporization of water

A simple model is introduced to interpret the heat of vaporization of water, which assumes the gaseous state as an ideal gas and the condensed state as an ideal solid. Making the approximations _j » kT and _i « kT simultaneously for the vibrational energies of the molecules in the gaseous and condensed phases, respectively, in the temperature region near room temperature, the temperature dependence of the molar heat of vaporization of water is theoretically dL/dT=–5R. This is in excellent agreement with the experimental value dL/dT=–5.12R in the temperature range 273 <T<373 K.     

石蜡乳状液潜热输送材料的研究进展

石蜡乳状液潜热输送材料是由相变石蜡与水乳化而成的悬浮液,具有较大的热客,能量储存密度及输送密度远高于相同温差下的水,因此可以使循环流量大幅降低,从而降低循环能耗,实现节能.根据相变石蜡材料及应用背景不同,分别综述了低温石蜡乳状液潜热输送材料、高温石蜡乳状液潜热输送材料的研究现状.指出了石蜡乳状液潜热输送材料在导热性能和稳定性等方面存在的共性问题,并探讨了解决措施:纳米颗粒强化传热是提高其导热性能的有效方法,研制纳米级相变石蜡微乳液是提高稳定性的有效途径.     

The possibility of high-temperature heat capacity measurements by differential scanning calorimetry

We have been conducting series of heat capacity measurements by differential scanning calorimetry (DSC) on various latent thermal storage materials such as NaOH-NaNO₃. Our concern is now shifting to higher temperature applications of latent thermal storage: space solar dynamic power systems (solar thermal electric power generation systems in space) and so on. Such applications require storage materials which can be operated above 1000 K. Needs for heat-capacity measurements at higher temperatures are increasing. In the present paper, some results of our heat capacity measurements by DSC at intermediate temperatures are presented. Several items which should be considered in order to realize the heat capacity measurements above 1000 K by DSC are discussed.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

储氢材料的研究发展现状

简要介绍了合金、碳纳米管、络合物等几种主要储氢材料的储氢原理和近期研究进展。讨论了各类材料的储氢功能特点,认为进行催化复合掺杂、控制储氢材料的显微结构是提高材料储氢性能的关键。     

SiO2-乙酰胺复合储热相变材料的制备

采用溶胶-凝胶法将有机相变材料乙酰胺嵌入到SiO2网络空间内,制备了复合储热相变材料.通过对比实验,研究了相变材料的种类、相变材料的加入量及催化剂种类对复合材料性能的影响.研究结果表明:采用氨水作催化剂,乙酰胺作相变材料,可制备出储热能力高、疏松多孔的复合材料,复合材料的相变温度为69.1℃,相变潜热高达124.2J/g;且复合材料中包含相变材料的质量分数越高,其储热能力越高.     

Measurement of the heat of fusion of tantalum by a microsecond-resolution transient technique

The heat of fusion of tantalum was measured using a microsecond-resolution pulse-heating technique. The technique is based on rapid (about 100-s) resistive self-heating of a specimen by a high-current pulse from a capacitor discharge system and measuring the current through the specimen, voltage across the specimen, and radiance temperature of the specimen as functions of time. Melting of a specimen is manifested by a plateau in the radiance temperature versus time function. The time integral of the power absorbed by the specimen during melting yields the heat of fusion. Measurements gave a value of 34.8 kJ · mot^– for the heat of fusion of tantalum, with a total uncertainty of ±6%. Electrical resistivity of solid and liquid tantalum at its melting temperature was also measured.     

Measurement of the heat of fusion of tungsten by a microsecond-resolution transient technique

A microsecond-resolution pulse-heating technique was used for the measurement of the heat of fusion of tungsten. The method is based on rapid (100 to 125s) resistive self-heating of a specimen by a high-current pulse from a capacitor discharge system and measuring current through the specimen and voltage across the specimen as functions of time. Melting of a specimen is manifested by changes in the slope of the electrical resistance versus time function. The time integral of the power absorbed by a specimen during melting yields the heat of fusion. Measurements gave a value of 48.7 kJ · mol^–1 for the heat of fusion of tungsten with an estimated maximum uncertainty of ±6%. The electrical resistivity of solid and liquid tungsten at its melting temperature was also measured.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

能量桩群储热温度场模拟研究

能量桩储热技术是以太阳能和混凝土桩作为复合热源的热泵系统,在混凝土桩内部埋设换热管,利用太阳能集热板将热量通过混凝土桩中的换热管储存在土壤中。本文采用柱热源模型对桩群进行180天的连续储热过程模拟计算,对地下土壤温度场进行分析,得出4 m的桩间距下,能量桩间的储热相互影响较小,效果较佳。     

热处理温度对刚玉基耐火材料组织和微粒脱落的影响EI北大核心CSCD

为研究温度对刚玉基耐火材料组织和微粒脱落的影响,对粉末冶金高温合金粉末制备用刚玉基(Al_(2)O_(3))耐火材料进行950~1350℃不同温度保温60 min处理。采用XRD分析热处理前后耐火材料的结构,采用扫描电镜对各样品进行微观形貌观察和微区成分测定,并用黏附实验评价不同温度处理后耐火材料颗粒脱落性的改善情况,探索加热保温处理对减少颗粒脱落的机理。采用热冲击测试评价不同温度处理后耐火材料耐热冲击性,并测试耐火材料的显气孔率与体积密度。结果表明:随着加热温度升高,耐火材料中的铝酸钙黏结剂成分将逐步从CaAl_(2)O_(4)(CA)转化为CaAl_(4)O_(7)(CA_(2)),一方面耐火材料中细小的陶瓷颗粒逐步烧结在一起,直至形成相互连接的稳定网状结构;另一方面逐步在大颗粒骨料上润湿铺展并相互连接,最后形成对大颗粒的包覆,同时耐火材料微粒黏附力将随着加热温度的升高逐渐增强。采用预热处理对于耐火材料的显气孔率、体积密度以及整体的耐热冲击性影响不大,但是随着温度升高,对于耐火材料表面在热冲击测试中的局部脱落程度和质量损失率有较明显改善。在保温60 min的条件下,加热温度在1150~1350℃时微粒脱落明显减少,其中1250~1350℃为较优预热温度段。