Preparation and hygrothermal performance of composite phase change material wallboard with humidity control based on expanded perlite/diatomite/paraffin

Phase change material(PCM)can reduce the indoor temperature fluctuation and humidity control material can adjust relative humidity used in buildings.In this study,a kind of composite phase change material particles(CPCMPs)were prepared by vacuum impregnation method with expanded perlite(EP)as supporting material and paraffin as phase change material.Thus,a PCM plate was fabricated by mould pressing method with CPCMPs and then composite phase change humidity control wallboard(CPCHCW)was prepared by spraying the diatom mud on the surface of PCM plate.The composition,thermophysical properties and microstructure were characterized using X-ray diffraction instrument(XRD),differential scanning calorimeter(DSC)and scanning electron microscope(SEM).Additionally,the hygrothermal performance of CPCHCW was characterized by temperature and humidity collaborative test.The results can be summarized as follows:(1)CPCMPs have suitable phase change parameters with melting/freezing point of 18.23°C/29.42°C and higher latent heat of 54.66 J/g/55.63 J/g;(2)the diatom mud can control the humidity of confined space with a certain volume;(3)the combination of diatom mud and PCM plate in CPCHCW can effectively adjust the indoor temperature and humidity.The above conclusions indicate the potential of CPCHCW in the application of building energy efficiency.

Emerging low-density polyethylene/paraffin wax/aluminum composite as a form-stable phase change thermal interface material

Thermal interface materials(TIMs) play a vital role in the thermal management of electronic devices and can significantly reduce thermal contact resistance(TCR). The TCR between the solid–liquid contact surface is much smaller than that of the solid–solid contact surface, but conventional solid–liquid phase change materials are likely to cause serious leakage. Therefore, this work has prepared a new formstable phase change thermal interface material. Through the melt blending of paraffin wax(PW) and low-density polyethylene(LDPE), the stability is improved and it has an excellent coating effect on PW. The addition of aluminum(Al) powder improves the low thermal conductivity of PW/LDPE, and the addition of 15wt% Al powder improves the thermal conductivity of the internal structure of the matrix by 67%. In addition, the influence of the addition of Al powder on the internal structure, thermal properties, and phase change behavior of the PW/LDPE matrix was systematically studied. The results confirmed that the addition of Al powder improved the thermal conductivity of the material without a significant impact on other properties, and the thermal conductivity increased with the increase of Al addition. Therefore, morphologically stable PW/LDPE/Al is an important development direction for TIMs.

Preparation of Paraffin/γ-Al2O3 Composites as Phase Change Energy Storage Materials

Paraffin/γ-Al2O3 composites as phase change energy storage materials were prepared by absorbing paraffin in porous network of γ-Al2O3.In the composite materials,paraffin was used as a phase change material(PCM)for thermal energy storage,and γ-Al2O3 acted as supporting materials.Characterizations were conducted to evaluate the energy storage performance of the composites,and differential scanning calorimeter results showed that the PCM-3 composite has melting latent heat of 112.9 kJ/kg with a melting temperature of 62.9 ℃.Due to strong capillary force and surface tension between paraffin and γ-Al2O3,the leakage of melted paraffin from the composites can be effectively prevented.Therefore,the paraffin/γ-Al2O3 composites have a good thermal stability and can be used repeatedly.

Preparation and Properties of Paraffin/PMMA Shape-stabilized Phase Change Material for Building Thermal Energy Storage

The composite phase change material(PCM) consisting of phase change paraffin(PCP) and polymethyl methacrylate(PMMA) was prepared as a novel type of shape-stabilized PCM for building energy conservation through the method of bulk polymerization. The chemical structure, morphology, phase change temperature and enthalpy, and mechanical properties of the composite PCM were studied to evaluate the encapsulation effect of PMMA on PCP and determine the optimal composition proportion. FTIR and SEM results revealed that PCP was physically immobilized in the PMMA so that its leakage from the composite was prevented. Based on the thermo-physical and mechanical properties investigations, the optimal mass fraction of PCP in the composite was determined as 70%. The phase change temperature of the composite was close to that of PCP, and its latent heat was equivalent to the calculated value according to the mass fraction of PCP in the composite. For estimating the usability in practical engineering, thermal stability, reliability and temperature regulation performance of the composite were also researched by TG analysis, thermal cycling treatments and heating-cooling test. The results indicated that PCP/PMMA composite PCM behaved good thermal stability depending on the PMMA protection and its latent heat degraded little after 500 thermal cycling. Temperature regulation performance of the composite before and after thermal cycling was both noticeable due to its latent heat absorption and release in the temperature variation processes. The PCP/PMMA phase change plate was fabricated and applied as thermal insulator in miniature concrete box to estimate its temperature regulation effect under the simulated environmental condition. It can be concluded that this kind of PCP/PMMA shape-stabilized PCM with the advantages of no leakage, suitable phase change temperature and enthalpy, good thermal stability and reliability, and effective temperature regulation performance have much potential for thermal energy storage in building energy conservation.

Direct incorporation of paraffin wax as phase change material into mass concrete for temperature control: mechanical and thermal properties

Taking advantage of heat absorbing and releasing capability of phase change material(PCM),Paraffin wax-based concrete was prepared to assess its automatic temperature control performance.The mechanical properties of PCM concrete with eight different Paraffin wax contents were tested by the cube compression test and four-point bending test.The more Paraffin wax incorporated,the greater loss of the compressive strength and bending strength.Based on the mechanical results,four contents of Paraffin wax were chosen for studying PCM concrete's thermal properties,including thermal conductivity,thermal diffusivity,specific heat capacity,thermal expansion coefficient and adiabatic temperature rise.When the Paraffin wax content increases from 10%to 20%,the thermal conductivity and the thermal diffusivity decrease from 7.31 kJ/(m·h·°C)to 7.10 kJ/(m·h·°C)and from 3.03×10−3 m2/h to 2.44×10−3 m2/h,respectively.Meanwhile the specific heat capacity and thermal expansion coefficient rise from 5.38×10−1 kJ/(kg·°C)to 5.76×10−1 kJ/(kg·°C)and from 9.63×10−6/°C to 14.02×10−6/°C,respectively.The adiabatic temperature rise is found to decrease with an increasing Paraffin wax content.Considering both the mechanical and thermal properties,15%of Paraffin wax was elected for the mass concrete model test,and the model test results confirm the effect of Paraffin wax in automatic mass concrete temperature control.

Synthesis and thermal characterization of the C-S-H/paraffin composite phase change material utilizing a discontinuous two-step nucleation method

The novel calcium-silicate-hydrate(C-S-H)/paraffin composite phase change materials were synthesized using a discontinuous two-step nucleation method.Initially,the C-S-H precursor is separated and dried,followed by immersion in an aqueous environment to transform it into C-S-H.This two-step nucleation approach results in C-S-H with a specific surface area of 497.2 m^(2)/g,achieved by preventing C-S-H foil overlapping and refining its pore structure.When impregnated with paraffin,the novel C-S-H/paraffin composite exhibits superior thermal properties,such as a higher potential heat value of 148.3 J/g and an encapsulation efficiency of 81.6%,outperforming conventional C-S-H.Moreover,the composite material demonstrates excellent cyclic performance,indicating its potential for building thermal storage compared to other paraffin-based composites.Compared with the conventional method,this simple technology,which only adds conversion and centrifugation steps,does not negatively impact preparation costs,the environment,and resource consumption.This study provides valuable theoretical insights for designing thermal storage concrete materials and advancing building heat management.

Preparation of Palygorskite-based Phase Change Composites for Thermal Energy Storage and Their Applications in Trombe Walls

Palygorskite/paraffin phase-change composites were prepared by the combination of purified palygorskite clay and sliced paraffin. Then, this composite was used in the Trombe wall to improve its energy storage ability. Further, its energy storage ability was compared to that of ordinary concrete wall through contrastive test. The experiments show that palygorskite clay is a type of clay mineral with strong adsorption ability, and the purity of natural palygorskite clay can reach up to 97.1% after certain purification processes. Paraffin is well adsorbed by palygorskite, and the test results show that the optimal adsorption ratio is palygorskite： paraffin = 2：1（mass ratio）. Palygorskite/paraffin phase change composites can be obtained by using palygorskite as the adsorbing medium to adsorb paraffin. The composite materials exhibit good heat storage（release） performance, which can store heat with increasing environment temperature and release heat with decreasing temperature. This property not only increases the inertia to environment temperature change, but also promotes the energy migration in different time and space, thus achieving a certain energy-saving effect. The application of palygorskite/paraffin phase change composite materials to the Trombe wall can significantly reduce the fluctuation of indoor temperature and enhance the thermal inertia of indoor environment. From the aspect of energy storage effect, the Trombe wall fabricated using PCMs is significantly superior to the concrete wall with the same thickness.

Preparation and Characterization of High-Temperature Non-Flowing Diurea/Paraffin/Oil Composites as Form-Stable Phase Change Materials

A series of form-stable phase change materials （FSPCMs） comprising paraffin as the latent heat storage material, diurea as the supporting material and base oil as the performance improvement agent were prepared. The diurea was synthesized in the system of paraffin/oil directly. A series of characterization was carried out for a deep understand- ing of shape stability and material properties of diurea-FSPCMs. The results showed that paraffin and base oil were packaged in the three-dimensional supra-molecular structures network which was formed by diurea. The dropping point of the prepared FSPCMs could reach 256 ℃ and the oil separation rate was as low as 1.19% at 100 ℃ for 30 h. The results of thermal properties tests showed that the prepared FSPCMs exhibited excellent thermal stability and the FSPCMs remained solid-like state in the temperature range from 25 to 200 ℃. This study proposes a novel method to prepare high-temperature non-flowing FSPCMs composites and methods to detect the thermal stability and shape stability of FSPCMs, which is helpful in understanding the shape stability mechanism and broadening the potential application of FSPCMs.

Preparation and Characterization of KNO3/Diatomite Shape-Stabilized Composite Phase Change Material for High Temperature Thermal Energy Storage

A new potassium nitrate （KNO3）]diatomite shape-stabilized composite phase change material （SS- CPCM） was prepared by the mixing and sintering method. KNO3 served as the phase change material （PCM） for thermal energy storage, while diatomite acted as the carrier matrix to provide the structural strength and prevent the leakage of PCM. It was found that KNO3 could be retained 65 wt% into pores and on surfaces of diatomite without the leakage of melted KNO3 from the SS-CPCM. The calculated filling rate of molten KNO3 that could enter into the disc-like shape pore of diatomite verified the scanning elec- tronic microscopy images of SS-CPCM. X-ray diffraction and Fourier transform infrared spectroscopy results showed that no reaction occurred between KNO3 and diatomite, performing good compatibility. Accord- ing to the differential scanning calorimetry results, after 50 thermal cycles, the phase change temperatures for melting and freezing of SS-CPCM with 65 wt% KNO3 were changed from 330.23 ℃ and 332.90 ℃ to 330.11 ℃ and 332.84 ℃ and corresponding latent heats varied from 60.52 J/g and 47.30 J/g to 54.64 J/g and 41.25 J/g, respectively. The KNO3/diatomite SS-CPCM may be considered as a potential storage media in solar power plants for thermal energy storage.

Experimental study and assessment of thermal energy storage mortar with paraffin/recycled brick powder composite phase change materials

Thermal energy storage recycled powder mortar(TESRM)was developed in this study by incorporating paraffin/recycled brick powder(paraffin/BP)composite phase change materials(PCM).Fourier transform infrared and thermogravimetric analysis results showed that paraffin/BP composite PCM had good chemical and thermal stability.The onset melting temperature and latent heat of the composite PCM were 46.49°C and 30.1 J·g−1.The fresh mortar properties and hardened properties were also investigated in this study.Paraffin/BP composite PCM with replacement ratio of 0%,10%,20%,and 30%by weight of cement were studied.The results showed that the static and dynamic yield stresses of TESRM were 699.4%and 172.9%higher than those of normal mortar,respectively.The addition of paraffin/BP composite PCM had a positive impact on the mechanical properties of mortar at later ages,and could also reduce the dry shrinkage of mortar.The dry shrinkage of TESRM had a maximum reduction about 26.15%at 120 d.The thermal properties of TESRM were better than those of normal mortar.The thermal conductivity of TESRM was 36.3%less than that of normal mortar and the heating test results showed that TESRM had good thermal energy storage performance.

Multifunctional HDPE/CNTs/PW composite phase change materials with excellent thermal and electrical conductivities

The risk of leakage and low thermal conductivity severely hinder the wide application of phase change materials(PCMs).In this work,the high-density polyethylene/carbon nanotubes(HDPE/CNTs)porous scaffolds were successfully fabricated via a sacrificial template method followed by the general melt blending and water solvent etching.Subsequently,a series of paraffin wax HDPE/CNTs/PW composite PCMs were obtained combined with the simple vacuum impregnation method.The obtained HDPE/CNTs porous scaffolds can effectively avoid the leakage of PW,meanwhile,the thermal conductivity and electrical conductivity of HDPE/CNTs/PW-3:7 are increased by 2.94 times and 13 orders of magnitude compared with the HDPE/PW-3:7 respectively,also,it exhibits high phase change enthalpy(153.95 J/g for melting enthalpy and 152.82 J/g for crystallization enthalpy).From the above perspectives,the HDPE/CNTs/PW-3:7 has promising potential value in the application of light-to-thermal conversion,electro-to-thermal conversion and thermal energy storage.

新型复合相变储能材料Na/Paraffin的制备与性能分析

为提升广泛应用于相变储能领域的石蜡的导热系数,在手套箱内将导热系数高、熔点低、密度小的金属Na与石蜡复合为Na/paraffin新型相变储能材料,并对其导热系数、相变潜热及储/放热特性进行研究。结果表明:5%Na/95%paraffin复合相变储能材料导热系数较纯石蜡提高了17.6倍,储/放热速率均较纯石蜡提升了1倍;经过200次循环实验后,3%Na/97%paraffin复合相变储能材料相变温度由60.58℃下降到59.65℃,相变潜热由166.7520J·g^(-1)下降到160.5632J·g^(-1),热导率由2.33W·m^(-1)·K^(-1)减少到1.98W·m^(-1)·K^(-1)。

石蜡/碱改性硅藻土/膨胀石墨复合相变储热材料的制备及性能

通过碱处理,优化了硅藻土(DIA)的孔隙结构,提高了孔隙率,增加了石蜡(paraffin)负载量。通过直接浸渍法制备了新型性状稳定的石蜡/碱改性DIA/膨胀石墨(EG-alDIAP)复合材料,并研究了其结构与性能的关系。结果表明,复合相变材料的石蜡负载量从47.4%提高到了61.1%,进而提高了复合材料的储热性能;向改性DIA中添加膨胀石墨(EG)提高了复合材料的传热能力,添加质量分数10%EG时导热系数提高了113%(从0.276 W·m^(-1)·K^(-1)提高到了0.589 W·m^(-1)·K^(-1))。随着EG含量的升高,复合相变材料的相变潜热有所增加,但化学相容性、稳定性等无明显变化。含10%EG的石蜡/碱改性DIA复合材料具有可靠的储能性能、良好的温度调节性能和蓄放热能力。

由石蜡基相变材料和煤渣改良的粉砂土的冻融性能

【目的】针对季节冻土区渠道的衬砌结构因冻融作用而受损的现状,同时为了解决石蜡基相变材料(phase change materials, PCM)的泄露,并满足煤渣的再利用需求,研究石蜡基PCM和煤渣对土体冻融性能的影响。【方法】以粉砂土为研究对象,选取石蜡基PCM和煤渣作为改良剂,制备石蜡基PCM改良土和石蜡基PCM-煤渣改良土;通过冻融循环作用下的体积变化率试验、无侧限抗压强度试验,微观结构及潜热研究土体的体积和无侧限抗压强度的变化。【结果】石蜡基PCM能抑制粉砂土的冻融变形,质量分数为8%时2种改良土的体积变化率最小;随着冻融循环次数的增加,土体的无侧限抗压强度均降低,降低速率先大后小;循环次数相同时,加入煤渣的改良土的无侧限抗压强度均大于未加入煤渣的;冻融循环9次后,石蜡基PCM质量分数为10%的石蜡基PCM改良土的无侧限抗压强度最低;2种改良土的结构比粉砂土更密实、稳定;潜热的吸收或释放延缓了土体冻融过程。【结论】将石蜡基PCM和煤渣共同掺入粉砂土,能控制土体的冻融变形且效果稳定,改善土体的冻融性能,减轻季节冻土区输水渠道衬砌结构的冻害,提高煤渣的利用率。

膨胀石墨基相变储能材料的制备及性能研究

以膨胀石墨作为主导热材料,石蜡作为相变储热材料,通过真空浸渍法制备了膨胀石墨-石蜡复合相变储能材料,研究了石蜡质量分数对复合相变储能材料微观形貌、物相结构及热性能的影响。结果表明,膨胀石墨和石蜡反应后生成的复合相变储能材料主要依靠物理吸附结合,石蜡均匀覆盖在膨胀石墨的表面以及孔隙中,当石蜡质量分数为91%时,复合相变储能材料的密封性和结构致密性最佳,几乎不发生泄露。随着石蜡质量分数的增加,复合相变储能材料的熔点逐渐增大,热分解温度逐渐提高,石蜡质量分数91%的复合相变储能材料相比石蜡质量分数85%的相变材料热分解温度提高了约15℃。随着石蜡质量分数的增大,复合相变储能材料的导热系数和热扩散系数持续降低,密度先降低后增加,比热持续增大。当石蜡质量分数为94%时,复合相变储能材料的导热系数和热扩散系数均为最低值,分别为2.492 W/(m·K)和0.605 mm^(2)/s;当石蜡质量分数为91%时,复合相变储能材料的密度为最小值0.794 g/cm^(3),对应比热为5.462 J/(g·K)。分析可得,石蜡质量分数为91%的复合相变储能材料的综合性能最佳。

硅藻土基定形相变材料的制备及应用进展

硅藻土是硅藻植物经过漫长的沉积成岩而形成的一种非金属矿物。硅藻土具有丰富微孔、耐高温、耐腐蚀性、价格低廉和资源丰富等优点,作为一种良好的吸附载体材料而受到广泛关注。介绍了硅藻土的结构特点并归纳了硅藻土常见的几种改性方法,综述了硅藻土基定形相变材料的种类及制备方法,总结了该材料在建筑领域的应用进展,分析了现阶段硅藻土基定形相变材料研究中存在的问题,并提出未来工作中需要关注的重点,以期为其规模化推广应用提供参考。

不同温度条件下相变石蜡力学性能分析

对3种不同相变温度的石蜡材料(PCM-28、PCM-18和PCM-10)在不同温度下的基本力学性能参数进行了系统的压缩实验,计算出对应的弹性模量和泊松比。结果表明:PCM-18和PCM-10的抗压强度随温度的降低而有所提高,但PCM-28的抗压强度随温度的降低反而呈现出下降趋势。在单轴压缩条件下PCM-28和PCM-18的应力-应变曲线主要经历了压实阶段、弹性变形阶段、裂纹扩展阶段和裂纹后破坏阶段4个明显阶段,最终表现为脆性破坏。PCM-10在经历压实阶段和弹性变形阶段后进入塑性阶段,曲线发展近似水平,且整个过程无明显裂纹出现。

石蜡/膨胀石墨复合定形相变材料的制备及季节适应性研究

以石蜡与白油混合制成的复合相变石蜡作为相变主体材料,以不同质量分数的膨胀石墨作载体材料,应用熔融共混方法,制备出5种不同比例的复合定形相变材料,对其进行吸附性能、热物性能测试,确定了复合定形相变材料的最优配比,并采用数值模拟方法研究该复合定形相变材料在冬、夏两季的适应性。结果表明:复合定形相变材料的最优配比为:膨胀石墨的质量分数为7%,复合相变石蜡的质量分数为93%,复合相变石蜡中52#切片石蜡与3#白油质量比为55∶45;该配比复合定形相变材料的相变温度为27.5℃,相变潜热为83.56 J/g,质量损失率为2.12%,导热系数为0.5316 W·m^(-1)·K^(-1);作为建筑外墙材料时,该复合定形相变材料能够平缓峰谷热流、减小温度波动,且在夏季的适应性强于冬季。研制的石蜡/膨胀石墨复合定形相变材料有望作为建筑调温相变材料在夏热冬冷地区应用。

石蜡Pickering乳液及其微胶囊相变非织造材料的制备与性能

Pickering乳液固含量和储存稳定性等性能显著优于传统乳液,但是,其乳化剂品种仍然稀缺,以苯乙烯(St)、甲基丙烯酰氧乙基三甲基氯化铵(DMC)为主要单体,二乙烯基苯(DVB)为交联剂,乙醇为助溶剂,用无皂乳液聚合法制备了阳离子型共聚物颗粒(P(St-co-DMC)),并将其作为乳化剂制备了石蜡Pickering乳液;并将石蜡乳液浸渍粘胶水刺非织造布制备石蜡微胶囊相变材料(Vis-PCM)。借助红外光谱仪、扫描电子显微镜、热重/差热联用仪、差示扫描量热仪和接触角测量仪等对共聚物及相变材料微观结构与性能进行表征与测试。实验结果表明:随着DMC用量、引发剂用量和乙醇含量的增加,单体转化率先增大后减小,P(St-co-DMC)粒径和分散指数先减小后增大,其Zeta电位则先快速增大而后趋于恒定,而亲水性持续增强;所得石蜡Pickering乳液的油水体积比高达3∶1,储存稳定性超过3个月;Vis-PCM的相变潜热高达139.3 J/g,经过20次冷热循环处理后,Vis-PCM中的石蜡泄漏率仅0.6%。本文制备的Vis-PCM具有良好的储热与放热性能,在相变储能领域具有广阔的应用前景。

离子交联型石蜡基导热增强定型相变材料的制备及其性能

对石蜡(PA)进行接枝改性、自乳化得到PA乳液。在乳液颗粒形态下将接枝产物分散在乳化层,常温条件下通过乳液颗粒间的空间分布及离子交联,对导热材料形成内锁、铆结,并加Cu粉增强导热制备了PA基导热增强定型相变材料(记作PA@Cu),与定量PA于80℃浸渍吸附20 min,得到吸附PA的PA@Cu(记作PA@Cu-PA),并研究了其元素结构、表观形貌、相变焓、导热性能、热稳定性。结果表明:当Cu粉用量为16 g时,PA@Cu-PA导热系数0.468 W/(m·K),结晶焓-133.27 J/g,在85℃时无明显泄漏,热分解温度384.5℃,储能性能与热稳定性能良好。