三水合乙酸钠/蛭石复合相变蓄热材料性能优化研究

采用真空浸渍法将三水合乙酸钠（sodium acetate trihydrate,SAT）吸附在膨胀蛭石（expanded vermiculite,EV）微孔内,选择EV吸附SAT能力最佳的质量比为1:6。通过扫描电子显微镜（scanning electron microscopy,SEM）观察复合相变材料（composite phase change material,CPCM）的微观结构,显示EV微孔几乎完全被SAT填充。X射线衍射（X-ray diffraction,XRD）表明SAT与EV化学相容性较好,二者仅发生物理相互作用。通过差式扫描量热法（differential scanning calorimetry,DSC）测试EV在最大吸附能力下,复合材料的相变温度为57.6℃,接近SAT理论相变温度58.1℃;相变潜热为238.8kJ/kg。热重分析（thermogravimetric analysis,TG）结果显示复合材料热稳定性良好。因为EV负载体将SAT间隔为无数微单元,有效改善SAT相变过程中过冷和相分离现象,起到成核剂和悬浮剂的作用。实验研究结果表明,制备的CPCM具有较好的热物性以及稳定的热循环性能,有望成为相变蓄热材料应用于冬季供暖。     

十水硫酸钠/膨胀蛭石薄膜复合相变材料的制备及性能分析北大核心CSCD

利用膨胀蛭石(EV)丰富的孔隙结构,采取真空吸附法和薄膜真空封装技术制备了一种十水硫酸钠/膨胀蛭石薄膜复合相变材料(简称薄膜相变材料)。用扫描电子显微技术(SEM)、X射线衍射技术(XRD)、自制温度参比相变潜热测试箱等表征测试手段,分析了薄膜相变材料的过冷和相分离等问题。结果表明,十水硫酸钠中掺入50%EV时,EV内部孔隙负载力达到饱和;在EV和硼砂共同作用下,经步冷曲线测得薄膜相变材料的过冷度为0.5℃;经薄膜真空封装后,十水硫酸钠均匀负载于EV层状结构内部,50%EV掺量的薄膜相变材料相变潜热在105 J/g以上,经300次相变循环后材料相变潜热趋于稳定,在500次相变循环后材料相变潜热保持在90 J/g以上,潜热留存率83.45%,循环性能优于常压封装下同种材料。薄膜真空封装技术获得膨胀蛭石对十水硫酸钠的良好负载效果,相变材料能够有效抑制十水硫酸钠的过冷和相分离等问题,具有较高的相变循环寿命。     

双层相变材料组合式蓄冷装置的性能研究CSCD

实验测试了两种相变温度分别为-5.4℃和-9.6℃、相变焓分别为132 kJ/kg和173 kJ/kg的十三烷和十二烷在不同组合模式下对蓄冷装置温度变化的影响。结果表明,十三烷在外层、十二烷在内层的组合模式,尽管总相变潜热在所有组合中仅排第三,但蓄冷装置将内壁温度控制在0℃以下的时间最长,与双层同为十二烷的工况相同,高于双层同为十三烷及十三烷在内十二烷在外层的模式。相变温度更高的材料在外层,可以降低环境热量传递至蓄冷装置内部的速率,延长蓄冷时间,有利于提高蓄冷装置的性能。     

Na_2SO_4·10H_2O复合相变储能体系的热力学测试

制备了一种Na2SO4.10H2O共晶相变蓄冷材料,其相变温度在8℃左右,可作为空调蓄冷材料。本文主要研究了复合相变体系的热化学性质和材料的相变特性。本研究测定出材料的相变潜热为114.37kJ/kg,固体平均比热容为4.68kJ/(kg.K),液体平均比热容为16.18kJ/(kg.K)。材料的主要成分为Na2SO4.10H2O,NaCl,NH4Cl,羧甲基纤维素(CMC)等,其主要特点是原料来源丰富,潜热和显热蓄冷量较大。     

复合相变材料蓄冷箱的保温性能研究

为了提供医学用品在冷链运输过程要求的低温环境，解决相变材料易泄露和导热系数低的问题，采用熔融共混法制备由十四烷、烯烃嵌段共聚物(OBC)和膨胀石墨(EG)组成的复合相变材料(CPCM)。利用复合相变材料制备蓄冷箱，利用COMSOL软件建立三维数值模型，并对其保温性能进行分析。结果显示：将复合材料应用于蓄冷箱中可以维持2～8℃的温度区间350 min，环境温度为37℃时，蓄冷箱内2～8℃的温度区间也可保持220 min。无源CPCM蓄冷箱系统在高温下也具有较好的保温能力，能够满足短途冷链运输的要求。     

空调蓄冷材料及蓄冷球内非固定融化问题的研究

通过实验方法研究了空调蓄冷材料的相变温度、相变潜热和比热等热学性能。并对该种蓄冷材料制成的蓄冷球进行了释冷特性的研究,探讨了蓄冷球内固液密度差引起的固态物上浮对蓄冷球融化释冷的影响,得到了融化率随时间的变化关系。结果表明:该蓄冷材料融解热为149.4kJ/kg,相变温度为7.9℃,该相变材料可作为空调蓄冷材料,蓄冷球的直径及固液密度差对融化释冷特性有较大影响。     

多孔基无机玻璃-熔盐复合相变材料蓄热性能的实验研究

基于熔融浸渗法和黏结封装法,以多孔基作为基体材料,分别采用无机玻璃粉与熔盐作为相变材料开展实验,探究储热样本的最佳制备工艺流程。考察了复合相变蓄热体的显微结构及物相组成特征,分析了复合相变蓄热材料的质量损失率,并对蓄热体进行蓄热性能分析及高温抗压强度测试。实验结果表明,采用黏结封装法,以氯化钠作为相变材料,加盖圆柱形三角孔蜂窝陶瓷基体作为载体,设定6.5℃/min的升温速率,烧结温度至800℃,保温30 min,可制备蓄热性能较为优异的复合相变蓄热材料。复合相变蓄热材料的蓄热密度为445.5 kJ/kg,该蓄热体在800℃条件下高温抗压强度达到75.9 MPa,具有良好的蓄热性能和力学性能。     

Preparation and thermal property of a tetradecane-octanoic acid eutectic phase change material

采用低共熔法研制了一种相变温度在0~3℃的二元有机相变蓄冷材料,该材料由十四烷和正辛酸按一定比例混合组成。首先通过理论计算预测二元最低共熔混合物的比例,确定其理论最低共熔点温度以及潜热值,然后围绕共晶点配制了5种不同比例的混合物。通过差示热量扫描仪、步冷曲线、Hot disk热常数分析仪测量其热物性,并利用高低温交变箱进行循环稳定性实验。当十四烷和正辛酸的摩尔质量比为51：49时,有最低共熔点温度为1.0℃,相变潜热为191.8 J/g,热导率为0.379 W/（m·K）。对其进行100次充放冷实验,循环后相变温度为0.9℃,相变潜热为191.5 J/g,相变蓄冷时间缩短了24.3%,热稳定性良好。实验结果表明,十四烷-正辛酸有机复合相变材料在低温储能中有可观的应用价值。     

污泥掺混木屑水解残渣为载体的复合相变材料循环热性能研究

本文以污泥水热解残渣资源化为目标,采用真空吸附法将污泥/木屑水热解的残渣吸附三水乙酸钠制备复合相变储热材料。对水热解残渣进行BET和粒径分析的表征,通过同步热分析仪、XRD及水浴中熔化-凝固多循环对复合储热材料的储热能力、相变温度、热循环稳定性等性能参数进行分析。实验结果表明,本文制备的复合相变储热材料无需添加增稠剂或悬浮剂等助剂,借助污泥残渣本身特有的均匀粒径和细微粒度特性以及木屑挥发分析出对残渣的造孔重整,作为载体可有效改善常规水合物作为储热材料的相变过冷度和相分离问题。封装尺度对储热材料的相变潜热和稳定性影响较小,100次循环后的潜热实际值与理论计算值（219.8kJ/kg）相差仅为-0.5%~0.4%,化学组分也没有变化,可见该复合储热材料既具有优良的热稳定性也具有可靠的化学稳定性。     

N掺杂多孔碳海绵定形芒硝基复合相变材料的制备及其热性能北大核心CSCD

芒硝相变储能材料作为一种潜热值高、来源广泛的无机水合盐,因存在相分层、过冷度等问题,限制了其在储能领域的广泛应用。本工作以N掺杂多孔碳为载体,将芒硝相变储能材料与N掺杂多孔碳复合,解决芒硝相变储能材料在实际应用中存在的问题。基于水热反应在聚氨酯泡沫上负载N原子,随后通过高温碳化得到N掺杂的多孔碳海绵(NPCS-M),并将其作为Na_(2)SO_(4)·10H_(2)O/Na_(2)HPO_(4)·12H_(2)O共晶盐的载体,最终制备出N掺杂多孔碳海绵封装的芒硝基复合相变材料(NPCM)。结果表明:N掺杂多孔碳海绵为蜂窝状结构,N含量为4.3%,比表面积为42.52 m^(2)/g,该材料对共晶盐的吸附量达到了自重的120倍。同时研究了该材料在5~60℃温度范围内循环1000次、3000次和5000次后的固液相变性能,经5000次循环后,该复合相变材料的潜热仍在130 J/g以上,且有降低共晶盐多次循环后过冷度的作用。该N掺杂多孔碳海绵复合相变材料在储能领域具有广阔的应用前景。     

蓄冷型LNG重卡冷能利用空调系统性能研究

提出了一种具有蓄冷功能的LNG重卡冷能利用空调系统,阐述了LNG重卡冷能利用空调系统的设计原理,基于Aspen plus软件模拟了系统流程,并对系统性能进行了分析。研究结果表明,在设定工况参数下,循环风量为520.00m~3/h时,蒸发器侧送风温度为19.85℃,空调制冷量为3.704kW,满足重卡3.500kW的制冷需求,同时,蓄冷器蓄存冷量0.410kW,可适应重卡多工况下空调系统的正常运行。此外,搭建静态实验台验证系统可行性,并将实验结果与同工况下模拟结果对比,二者曲线趋势一致,系统运行效果良好,制冷能力能够满足实际需要。     

冷库现状及冷库节能途径

论述了当前我国冷库行业的发展现状,指出了我国冷库设计、建设和管理等方面存在的问题,并给出了一些节能的方法。     

Improving cold flow properties of canola-based biodiesel

Methods for improving the cold flow properties of canola-based biodiesel are described. Freezing point depression via dilution is evaluated through controlled studies of methyl stearate freezing in seven different solvents, and methyl palmitate in three solvents. Without accounting for solute activity, the Hildebrand equation can predict the impact of methyl stearate freezing point in an alkane solvent (pentane) to within 4 °C. However, there is wide deviation for the other solutions, indicating wide ranging solute activities in these solvents. Dilution in toluene results in the greatest freezing point depression. In addition, several polymeric additives are screened for their effectiveness as biodiesel pour point depressants. After examining more than 13 polymers, including several alkyl methacrylate homo- and copolymers, it is shown that poly(lauryl methacrylate) homopolymer most effectively improves the biodiesel cold flow properties. At 1% loading, poly(lauryl methacrylate) lowers the pour point by as much as 30 °C and the low temperature filterability point (LTFP) by as much as 28 °C. When evaluating the impact of polymer concentration, it is shown that poly(lauryl methacrylate) concentrations of 0.14% perform poorly, whereas 0.5% has only a slightly lower impact than 1%. Concentrations above 1% exhibit no improvement. Finally, it is shown that a limited amount of mixing can notably reduce the LTFP in several samples.     

引入最佳冷化系数优化设计建筑楼宇冷热电系统

提出了“最佳冷化系数”的概念,对最佳冷化系数的应用及理论意义进行了论述,指出最佳冷化系数在建筑楼字冷热电（BCHP）设备选型中的意义,可使目前在空调制冷机组选型普遍偏大的问题得到改善,并结合实例给出了论证。     

Optimization of cold end system of steam turbine

An optimization of the movement characteristic of the cold end system of the steam turbine was conducted from an overall consideration of the condenser and the circulation water pump. An analysis method based on thermodynamics theory that fixes coupling characteristic between the best vacuum and the best circulation discharge of water was proposed. The proposed method was applied to the optimized analysis of the operating mode of the cold end system of a 300 MW unit in a power plant. __________ Translated from Thermal Turbine, 2007, 36(1): 19–23 [译自: 热力透平]     

Analysis of Cold Flowfield of Multi—Annular Opposed Jets

The technique of the use of multi-annular opposed jets as different from using swirl and bluff body createsan excellent recirculation zone with desired size in a large space.The size of recirculation,the magnitude ofreverse velocity and turbulence intensity are much greater than those formed by bluff body.Factors affectingthe flowfield include the velocity ratio of the opposed jets to the primary air J,the diameter and constructionof the opposed jet ring,secondary air velocity and configuration,and confined or unconfined flow condition andso on.This method is a promising way for flame stabilization in combustion technology.     

Analysis of a latent heat cold storage unit

This paper presents a conduction based model for solving the phase change heat transfer problem around a vertical cylinder submersed in the phase change medium. The energy equation is coupled to the flow problem by an energy balance. The system of equations is solved numerically by using the average control volume technique and the ADI approach. The results show the effects of the variation of the Biot number, Stefan number, the inlet fluid temperature and the ratio of the outer to the inner tube radius on the solidified mass fraction, NTU, effectiveness and the time for complete solidification. © 1997 by John Wiley & Sons, Ltd.     

A cold model analysis of solid waste incineration

A cold physical model to a scale of 1:33 of a solid waste incinerator was designed and constructed of transparent material. Experimentation aimed at optimizing gas flow patterns in the furnace for low-pollutant combustion. Flames were simulated by acid-base neutralization. Secondary air flow distribution and direction were identified as the controlling parameters of the flow pattern. The best possible air distribution for a desired flame shape and gas mixing was determined. Streamline plots for verification of the mathematical models were obtained.