Ba(OH)_2·8H_2O复合相变材料及其在太阳能光伏/热集热器上的释热特性

开发了一种熔点为78℃的八水氢氧化钡复合相变材料,通过添加成核剂使复合相变材料的过冷度降低3~5℃,结合纳米技术使材料的热导率提高了11.7%。基于包含复合相变蓄热材料与石蜡、水蓄热的梯级蓄热太阳能光伏、光热集热器,对该新型材料的释热特性进行了实验,实验结果表明,八水氢氧化钡复合相变蓄热材料无过冷,在其相变温度上相变平稳。在水流量为90 L·h~(-1),环境温度为20℃时,集热系统可以有效地储存太阳能,以50℃为参考点放热时间长达60 min以上,且在放水前20 min内,系统的出水温度都高于70℃,因此该系统能够在降低太阳电池工作温度的同时,满足日常生活需求。     

无机相变材料CaCl2·6H2O的过冷特性

CaCl₂·6H₂O作为一种常见的常温无机水合盐相变材料,由于成本低、易获取、蓄热强而受到广泛的关注。按无水CaCl₂与H₂O的质量比为1.027：1制备了CaCl₂·6H₂O,经X射线衍射（XRD）表征其晶体结构;通过添加成核剂SrCl2·6H₂O和Ba（OH）₂对CaCl₂·6H₂O改性,发现两者的联合作用可抑制过冷,10次熔化-冷却循环平均过冷度1.07℃。采用差示扫描量热仪（DSC）测定CaCl₂·6H₂O添加成核剂前后相变潜热,发现潜热由223.54 J·g^-1降至160.41 J·g^-1;为了扩大CaCl₂·6H₂O相变温度的范围,通过添加质量分数分别为5%、10%、15%、20%和25%的MgCl₂·6H₂O,发现相变温度随MgCl₂·6H₂O质量分数的升高呈线性降低,但不宜超过20%;选取CaCl₂·6H₂O-20% MgCl₂·6H₂O二元共晶盐相变储热体系为改性目标,通过添加1% SrCl2·6H₂O和0.5% CMC,过冷度降至0.57℃,相变潜热为141.09 J·g^-1,低于单独组成盐CaCl₂·6H₂O的潜热223.54 J·g^-1和MgCl₂·6H₂O的潜热163.35 J·g^-1。研究表明,CaCl₂·6H₂O作为无机相变材料具有显著的应用价值。     

KAl(SO4)2·12H2O-MgSO4·7H2O复合相变体系储能特性的探究

KAl(SO_4)_2·12H_2O和MgSO_4·7H_2O作为常见的水合无机盐相变材料,具有相变潜热较大、原料较廉价易得等优点。筛选并制备出KAl(SO_4)_2·12H_2O和MgSO_4·7H_2O质量配比为6:4的复合相变材料,取纯体系样品4份加入质量比(wt%)分别与1%Na_2B_4O_7·10H_2O、1%石墨粉、2%MgCl_2、2%AlCl_3进行混合改性。结果表明:室温条件下加入1%Na_2B_4O_7·10H_2O成核剂体系的储热特性优于加入1%石墨粉、2%MgCl_2、2%AlCl_3成核剂的体系,不存在过冷现象,降温过程中相变放热持续时间长;TG曲线和DSC曲线表明纯体系、1%Na_2B_4O_7·10H_2O成核剂体系二者质量损失分别为37%和42%,循环后体系DSC曲线与未循环体系趋势一致,但可看出KAl (SO_4)_2·12H_2O-MgSO_4·7H_2O-1%Na_2B_4O_7·10H_2O(Times10)体系的主峰相比于KAl(SO_4)_2·12H_2O-MgSO_4·7H_2O纯体系更窄,峰值温度更低,峰积分面积更小,表明循环后体系的整体相变焓降低。     

应用于太阳能相变蓄热PC构件升温养护建筑的复合相变材料热物性

预制混凝土（PC）构件蒸汽养护工艺以消耗大量化石能源为代价。本研究结合本文作者课题组研制的复合相变材料热特性以及预制混凝土构件蒸汽养护工艺特点,基于被动式太阳能相变蓄热PC构件升温养护建筑一体化设计理念,将复合相变材料应用于升温养护建筑主朝阳墙体内表面,结合Energy Plus能耗模拟软件及试验研究的方法,开展了关于不同热物性复合相变材料对新型升温养护建筑热工性能影响的研究。研究结果表明：较GH-33复合相变材料,主朝阳墙体内表面采用GH-37复合相变材料,墙体内表面温度夜间平均提高3.4℃;PC构件上部表面温度夜间平均提高1.4℃;实验期间复合相变材料的蓄放热速率较前者平均提高62%。研究可为PC构件养护工艺中可再生能源利用、低碳环保生产,提供一种新的途径和方法参考。     

太阳能光伏产业的热场材料

单晶硅、多晶硅等硅材料是实现光电转换的主要材料之一.生产高纯度的多晶硅和单晶硅不仅需用大量的石墨材料,而且耗能量也非常大.随着产量的提高和生产设备的大型化,碳/碳复合材料坩埚和加热元件以及石墨纤维保温筒将是发展方向.高纯度和大尺寸热场材料具有显著的社会和经济效益.     

CaCl2·6H2O/多孔Al2O3复合相变材料的制备与热性能

将CaCl2·6H2O作为相变材料,3%的硼砂作为成核剂,以多孔Al2O3作为基体,通过真空浸渍法和多孔Al2O3的毛细吸附作用,制得不同比例的CaCl2·6H2O/多孔Al2O3复合相变材料,并进一步对其微观结构和热性能进行了分析。N2吸附脱附等温线分析证明,多孔Al2O3具有较大的比表面积。SEM照片和FTIR光谱说明CaCl2·6H2O被成功吸附入Al2O3的多孔结构中。DSC曲线显示,复合相变材料的熔融潜热可达99.81 J/g,说明其具有良好的相变储热性能。     

膨胀石墨/石蜡复合相变材料的导电及发热特性

采用混合搅拌方法制备膨胀石墨（EG）/石蜡复合相变材料,测试分析了EG含量、施加电压与EG/石蜡复合相变材料体积电阻率的关系,研究了直接自发热和正温度系数（PTC）电阻发热时复合相变蓄热单元的发热特性。结果表明,随着EG含量或施加电压的增大,复合相变材料体积电阻率逐渐减小;施加电压对样品体积电阻率的影响与复合相变材料中EG含量有关,EG含量越高,施加电压对复合相变材料体积电阻率的影响越明显。当施加电压为4.0V时,EG质量分数分别为4%、5%、8%的复合相变材料体积电阻率分别只有0.5V时的0.481倍、0.185倍、0.068倍。基于复合相变材料导电特性,直接负载电压可实现复合相变材料电热转化和相变蓄热;结合PTC电阻发热可灵活控制复合相变蓄热单元加热功率,实现其快速充热。     

增稠剂对NH4Al(SO4)2·12H2O蓄放热性能的影响

利用电热恒温水槽、高低温交变试验箱搭建蓄放热实验平台,研究了9种增稠剂对NH₄Al(SO₄)₂·12H₂O蓄放热性能的影响,测试分析了NH₄Al(SO₄)₂·12H₂O改性后的循环稳定性能。结果表明,质量分数为2%的黄原胶、1%的瓜尔豆胶或1%的羟乙基纤维素均能较好改善NH₄Al(SO₄)₂·12H₂O的放热性能且对相变潜热的削弱程度不大,对应改性NH₄Al(SO₄)₂·12H₂O的主要参数变化为：熔点分别降低1.0℃、1.3℃、1.3℃,蓄热时长分别增加94%、35%、9%,蓄热相变平台分别增加125%、63%、5%,过冷度分别减小43%、45%、34%,结晶过程温度变化分别减小84%、87%、73%,放热时长分别增加27%、11%、50%,相变潜热分别减小5.8%、8.3%、4.1%。增稠剂对NH₄Al(SO₄)₂·12H₂O放热性能的改性效果会受到降解反应影响,而2%黄原胶的改性效果相对其他两种增稠剂较好,循环过程中改性材料的结晶过程温度始终保持在60℃以上。60次循环后,改性材料主要参数相比纯材料的变化为：熔点下降0.2℃,蓄热相变平台减小15%,蓄热时长增加13%,结晶过程温度变化减小87%,过冷度减小42%,放热时长增加36%,相变潜热减小1.6%。     

三水醋酸钠/甲酰胺复合相变材料的制备及性能

以甲酰胺(FA)为改性剂,采用熔融共混法对三水醋酸钠(SAT)进行改性得到新型SAT/FA复合相变材料(CPCM)。探讨FA质量分数(下同)对SAT/FA共混物(基体)相变焓及相变温度的影响。利用熔融-固化循环及步冷曲线, 系统探讨成核剂、增稠剂对复合材料相分离、过冷度及放热性能的影响。对新型SAT/FA CPCM的结构及性能进行XRD 、FTIR及DSC表征。结果显示:添加25%的FA于SAT中可形成SAT/FA低共融体;添加2% 十二水磷酸氢二钠成核剂和2%聚乙烯醇增稠剂形成的CPCM,过冷度低(2.67℃),放热时间长(10170 s),循环稳定性好, 相变焓高达233.9 kJ·kg^-1,相变温度40.88 ℃。可应用于相变蓄热地板辐射采暖。     

纳米材料/十四酸混合相变蓄热材料的制备与特性

选用纳米金属Cu和碳素材料石墨烯纳米片（GnPs）为改性剂分别添加至十四酸（MA）中,制备出Cu质量分数为1%、2%、3%和4%的Cu/MA混合相变蓄热材料及GnPs质量分数为1%、2%和3%的GnPs/MA混合相变蓄热材料,并对混合相变材料性能进行表征。结果表明：Cu/MA固态和液态热导率随Cu质量分数增加呈线性提高,1%（质量）GnPs/MA固态热导率较纯MA显著提高101.51%,随GnPs质量分数增加,热导率增幅减缓;FT-IR谱图表明Cu与MA及GnPs与MA间的混合均为物理作用;DSC结果显示添加Cu或GnPs可降低MA的过冷度和相变潜热,且随质量分数增加,相变潜热逐渐降低;4%（质量）Cu/MA和3%（质量）GnPs/MA放热时间相比于纯MA分别减少了23.4%和38.7%;4%（质量）Cu/MA和3%（质量）GnPs/MA在经历300次快速热循环试验后,晶体结构和相变温度基本保持不变,相变潜热分别降至168 J·g^-1和181 J·g^-1左右,仍满足蓄放热要求,两种材料均具有良好的热循环稳定性。     

太阳能光伏/热（PV/T）技术的研究进展

太阳能光伏/热（PV/T）技术是将光伏和光热结合在一起,可实现较高的太阳能利用率。本文首先简要介绍了PV/T集热器的概念、基本原理及分类。然后从PV/T集热器结构和运行参数两方面综述了近几年来国内外PV/T集热器的相关研究,对比分析了水冷型、制冷剂型和热管型3种类型PV/T的优缺点。概述了目前常用的PV/T性能评估和经济性分析的方法。最后指出了当前的PV/T集热器存在诸如结构复杂、工质渗漏、初始投资大等问题,并且缺少对其长期的动态性能研究。未来需对现有结构作进一步优化,同时开发新型PV/T集热器。     

Development of empirical relation to evaluate the heat transfer coefficients and fractional energy in basin type hybrid (PV/T) active solar still

The simple empirical relation is developed to estimate the glass cover temperature for known values of water and ambient temperatures in basin type hybrid (PV/T) active solar still. The empirical relation developed is based on outdoor experimental results of water and ambient temperature in the range of 14 °C to 92 °C, and 14 °C to 36 °C respectively. The results obtained for glass cover temperature using proposed relation are validated with the experimental as well as using a numerical results (obtained by numerical solution of heat balance equation) of solar still. The proposed glass cover temperature is obtained with a maximum relative error of 1.12% compared to the value obtained through a numerical solution. The maximum relative error in evaporative mode of energy transfers from water surface is obtained as 1.2%.     

Ion-exchange kinetics and electrical conductivity studies of polyaniline Sn(IV) tungstoarsenate; (SnO2)(WO3)(As2O5)4(C6H5NH)2·nH2O: a new semi-crystalline ‘polymeric-inorganic’ composite cation-exchange material

A new and novel electrically conducting ‘polymeric-inorganic’ composite cation-exchange material; polyaniline Sn(IV) tungstoarsenate was prepared by incorporating polyaniline into inorganic ion-exchanger material. It possessed improved ion-exchange capacity, high chemical and thermal stabilities, reproducibility and selectivity for some specific metal ions. Kinetic study of exchange for some divalent metal ions of alkaline earths and transition metals was carried out under the conditions favoring a particle diffusion-controlled ion-exchange phenomenon and some physical parameters such as self diffusion coefficient D₀, energy of activation E_a and entropy of activation ΔS* were determined. The temperature dependence of electrical conductivity of this composite material with increasing temperatures was measured by using 4-in-line-probe DC electrical conductivity measuring-technique. The conductivity values lie in the semiconductor region, i.e. in the range of 10⁻³ S cm⁻¹ that follow the Arrhenius equation. The energy of activation of electrical conduction for the composite was also calculated.     

Simultaneous CO2 capture and thermochemical heat storage by modified carbide slag in coupled calcium looping and CaO/Ca(OH)2 cycles

The simultaneous CO_2 capture and heat storage performances of the modified carbide slag with by-product of biodiesel were investigated in the process coupled calcium looping and CaO/Ca(OH)_2 thermochemical heat storage using air as the heat transfer fluid. The modified carbide slag with by-product of biodiesel exhibits superior CO_2 capture and heat storage capacities in the coupled calcium looping and heat storage cycles. The hydration conversion and heat storage density of the modified carbide slag after 30 heat storage cycles are 0.65 mol·mol~(-1) and 1.14 GJ·t~(-1), respectively, which are 1.6 times as high as those of calcined carbide slag. The negative effect of CO_2 in air as the heat storage fluid on the heat storage capacity of the modified carbide slag is overcome by introducing CO_2 capture cycles. In addition, the CO_2 capture reactivity of the modified carbide slag after the multiple calcium looping cycles is enhanced by the introduction of heat storage cycles. By introducing 10 heat storage cycles after the 10 th and 15 th CO_2 capture cycles, the CO_2 capture capacities of the modified carbide slag are subsequently improved by 32%and 43%, respectively. The porous and loose structure of modified carbide slag reduces the diffusion resistances of CO_2 and steam in the material in the coupled process. The formed CaCO_3 in the modified carbide slag as a result of air as the heat transfer fluid in heat storage cycles decomposes to regenerate CaO in calcium looping cycles, which improves heat storage capacity. Therefore, the modified carbide slag with by-product of biodiesel seems promising in the coupled calcium looping and CaO/Ca(OH)_2 heat storage cycles.     

Degradation of benzene,toluene ethylbenzene and p‐xylene (BTEX) in aqueous solutions using UV/H2O2 system

The homogeneous degradation of benzene (B), toluene (T), ethylbenzene (E) and p‐xylene (X) (BTEX) was studied in aqueous solutions, at pH 3.0, of hydrogen peroxide (5.8 mM ) under UV irradiation in a photoreactor equipped with a 300 nm lamp of light intensity 3.5 × 10^?5 Ein L^?1 min^?1. BTEX was substantially degraded by the H₂O₂/UV system, with >90% disappearing in 10 min of irradiation. The decomposition of BTEX was studied either as single or as multi‐component systems. The effects of irradiation time, amounts of H₂O₂ in molar ratios, rate of degradation and competition between components were thoroughly examined. It can be stated that the rate of BTEX degradation in mixture was higher than those for the individual components due to external effects of the absorption of UV light by the mixture, and their effects on enhancing the formation of OH^? radicals. The appropriate figure of merit, the electrical energy per mass (EE/M), was estimated at various molar ratios and it was confirmed that the best value was the one depicted for p‐xylene (0.065 kWh kg^?1). A theoretical model for the degradation pathway was proposed. Copyright © 2004 Society of Chemical Industry