石墨化碳泡沫导热性能研究

以煤焦油基沥青为原料,在420～450℃的范围内热解制备中间相沥青,用所制得的沥青在6～8MPa的压力下升温发泡,保温一段时间,然后再经过碳化和石墨化制得一种性能优良的导热材料--碳泡沫,其导热系数最高可以达到110W/(m·K).讨论了沥青中间相含量、发泡时的压力、保温时间、升温速率对泡沫导热性能的影响:随着中间相沥青含量的增加,所制备的碳泡沫的导热系数明显提高,中间相由0%提高到100%时,导热系数由77.5W/(m·K)上升到110W/(m·K);发泡时保温时间的影响相对于成型压力更为明显,保温时间从1h提高到4h,导热系数会由85 W/(m·K)上升到100W/(m·K);发泡的压力对导热系数的影响不是很明显.     

石墨烯填充对不同聚合物导热性能和热稳定性的影响

为研究同一制备方法下石墨烯质量分数对不同聚合物导热性能和热稳定性的影响,通过熔融共混法制备了石墨烯/聚酰胺(GE/PA6)、石墨烯/聚丙烯(GE/PP)、石墨烯/高密度聚乙烯(GE/HDPE)3种聚合物复合材料。结果表明,石墨烯能有效提高3种聚合物导热性能,当填充石墨烯质量分数达到10%时,PA6导热系数从0.32 W/(m·K)提升至1.30 W/(m·K);GE/PP导热系数从0.37 W/(m·K)提升至1.15 W/(m·K)、GE/HDPE导热系数从0.62 W/(m·K)提升至1.13 W/(m·K)。对制备的石墨烯聚合物复合材料进行热重分析。将纯聚合物与石墨烯质量分数1%,5%,10%的石墨烯聚合物复合材料对比,PA6的热稳定性逐渐提升,PP、HDPE的热稳定性先降低后升高。     

新型多腔孔陶瓷复合保温材料的制备及性能研究

通过原料及配方的创新,以硅酸铝纤维、玻化微珠等为原料制备了一种新型多腔孔陶瓷复合保温材料。研究了材料的导热性能和显微结构。结果表明:材料导热系数低,热面温度200℃时导热系数仅为0.050 W/(m·K),热面温度600℃时导热系数为0.084 W/(m·K);材料内部结构疏松,存在多级配的孔隙结构,孔隙尺寸在微米级以下。利用马弗炉进行保温性能测试,保温材料内表面温度600℃,厚度仅为139mm时,稳态时外表面温度即可低于46℃,散热损失仅为158 W/m~2,远远低于标准规定的最大散热损失266 W/m~2。将材料制成1cm厚度的块材时,材料能产生较大弯曲而不损坏,有利于对电厂高温管道进行包覆。     

柔性海泡石基气凝胶的制备及其保温隔热性能的研究

以海泡石为基质,聚乙烯醇为有机增强相,硅烷偶联剂KH-560和聚乙烯亚胺为交联剂,经冷冻干燥制备了具有优异保温隔热性能的柔性海泡石基气凝胶。其导热系数低至0.0374W/(m·K),轴向在经过80%的压缩形变后能达到100%回弹,径向在经过50%的压缩形变后也能达到100%回弹。该气凝胶有望作为保温隔热材料应用于建筑、隔热帐篷等领域。     

新型耐高温多层隔热结构研究

为了改善传统应用的多层隔热材料的耐温及隔热效果等性能,以耐高温硅酸铝纤维纸和石英纤维网为基体材料,疏水性SiO2气凝胶颗粒为隔热填料,采用粘结工艺制备了新型耐高温多层隔热结构.采用石英灯阵列光电加热装置测试该结构冷面温度随时间的变化情况,采用PBD-02P平板导热仪测试各个指定温度下的导热系数,采用扫描电镜表征胶层的微观形貌.研究改变疏水性SiO2气凝胶颗粒添加量对导热系数的影响,结果表明,当疏水性SiO2气凝胶颗粒与耐高温胶粘剂质量比为2∶40时制备出的试样具有最低导热系数.这种新型耐高温多层隔热结构最高使用温度可达1000℃,平均密度小于0.25g/cm3,热面温度为1000℃时最佳配比试样的导热系数仅为0.080W/(m·K).该结构优异的综合性能能够很好地应用于航空航天隔热领域.     

冷链物流用木基纤维保温包装材料的制备及性能的研究

目的 制备木基纤维保温包装材料,并提高它的保温性能。方法 以轻质天然木材为原料,通过化学脱木素制备木材纳米纤维多孔材料,再对木材纳米纤维多孔材料表面闭孔处理,制备出木基纤维保温材料。结果 基于瞬态平面热源法,当纤维同向平行放置时,木基纤维保温材料的导热系数为0.019 W/(m·K);当纤维异向交叉放置时,木基纤维保温材料的导热系数为0.023 W/(m·K),表明开发的这种材料有较好的保温性能。此外根据该种保温材料的缓冲系数–最大应力曲线可知,当最大静应力σ_m=0.63 MPa时,沿纤维同向平行叠放时,木基纤维保温材料的最小缓冲系数C=3.5;沿纤维异向交叉叠放时,木基纤维保温材料的最小缓冲系数C=4.2,可见保温材料的缓冲性能均与发泡聚苯乙烯(EPS)、发泡聚乙烯(EPE)的缓冲性能相近。结论 制备的轻质木基纤维保温材料兼具较好的保温和缓冲性能,有望用于冷链物流代替塑料保温包装材料。     

气凝胶纸蜂窝夹层板的隔热性能

为改善气凝胶复合材料的承压能力,设计了一种纸蜂窝作为夹层,两侧复合气凝胶复合材料的夹层板,并探究该夹层板能否取代聚氨酯泡沫,应用于冷库墙体保温夹层.利用导热系数仪测得的试验数据,对纸蜂窝、气凝胶复合材料、气凝胶纸蜂窝夹层板的隔热性能进行了分析,讨论材料厚度对气凝胶蜂窝夹层板导热性能的影响.结果表明:纸蜂窝的厚度较小时,气凝胶纸蜂窝夹层板的导热系数均低于聚氨酯泡沫板;当纸蜂窝厚度为10 mm、孔径为6 mm,气凝胶复合材料厚度为10 mm或15 mm时,气凝胶纸蜂窝夹层板的导热系数低于0.03 W/(m·K),满足我国保温隔热行业材料的使用要求.     

不同体积掺量的SiO_2气凝胶对砂浆性能的影响

以低导热系数的SiO_2气凝胶颗粒为保温骨料,采用等体积替换法替换砂浆中的沙制备SiO_2气凝胶砂浆,主要研究当SiO_2气凝胶颗粒的替换比例分别在10%,20%,30%,40%,50%和60%时,对砂浆的密度、力学性能、吸水率以及导热系数等性能的影响,并在此基础上,通过添加纤维、引气剂和胶粉来对砂浆做改性,重点研究了各掺量对砂浆导热系数的影响,结果表明,当其掺量分别为0.2%,0.05%和1%时,导热系数达到最低为λ=0.0859 W/(m·K)。     

纳米纤维素/聚酰亚胺气凝胶制备与性能研究

纳米纤维素气凝胶由于其良好的生物相容性、可再生性、可降解性以及较高的孔隙率等优异性能,在建筑隔热领域有着十分广阔的应用前景。为了更好地提升纳米纤维素气凝胶的保温隔热性能和力学性能,引入聚酰亚胺,制备了一种具有规则孔隙结构的复合纳米纤维素气凝胶。通过SEM、导热系数测试仪、红外成像仪等测试方法对其结构和性能进行表征。结果表明,当CNF∶PI的质量比为1∶1时,复合气凝胶的结构规则,孔径较小,在15～18μm左右,密度低至0.0413 g/cm³,压缩强度可达0.33 MPa,导热系数低至0.03159 W/(m·K),具有最优异的综合性能。     

玻璃纤维和碳纤维增强二氧化硅气凝胶复合材料的制备及性能研究

以正硅酸乙酯为前驱体,玻璃纤维和碳纤维为增强相,通过溶胶-凝胶和常压干燥分别制备了玻璃纤维增强型二氧化硅气凝胶(GF/SiO₂气凝胶)和碳纤维增强型二氧化硅气凝胶(CF/SiO₂气凝胶)复合材料,通过扫描电子显微镜、傅里叶红外光谱、比表面积和孔径分布测试仪、万能力学试验机、导热系数测试仪等手段对材料的结构和性能进行了测试表征,对比分析了玻璃纤维和碳纤维对SiO₂气凝胶复合材料结构与性能的影响。结果表明：玻璃纤维与SiO₂颗粒基体之间的界面结合较差,制得的GF/SiO₂气凝胶具有较差的力学性能(压缩强度=0.676MPa,应变=60%)和较高的导热系数[0.0410W/(m·K)];而碳纤维与SiO₂气凝胶颗粒具有较好的界面相互作用,制得的CF/SiO₂气凝胶具有良好的力学性能(压缩强度=1.225MPa,应变=60%)和低的导热系数[0.0342W/(m·K)]。     

梯度热障涂层热冲击性能研究

采用等离子喷涂的方法,分别获得了２ｍｍ ＺｒＯ２－ＮｉＣｒＡｌ和ＺｒＯ２－Ｎｉ／Ａｌ系梯度热障涂层。热冲击实验结果表明,两种涂层具有不同的失效机理。ＺｒＯ２－ＮｉＣｒＡｌ系的失效是由于基于基体氧化引起的涂层整体脱落;而ＺｒＯ２－Ｎｉ／Ａｌ系的失效是支径向裂纹扩展到Ｎｉ／Ａｌ底层氧化共同作用的结果。     

人体热适应性与热舒适

本文参阅国内外研究成果,讨论了人体热适应性与热舒适的关系,介绍了实验室研究中的适应性和实测调查研究的适应性,对影响人体热舒适的行为调节适应、心理调节适应以及生理调节适应进行了分析,认为热适应性研究对人体的热舒适具有重要意义.     

Thermal Coherent States and Thermal Squeezed States

Abstract

Various definitions of thermal coherent states and thermal squeezed states are compared and interrelated. Different ordering of squeezing, displacement and thermalizing operators is discussed in order to establish a relation between all definitions. A one-to-one correspondence is exhibited between general Gaussian density matrices in coordinate space and thermal squeezed states.     

车室内人体热舒适性的计算模型

在车室内热环境计算的基础上,借助于人体热调节系统以及人体生物热方程计算了人体温度场的分布,并且利用当量温度Teq去评价不同环境下人体的热舒适性。文中完成了一个典型算例,预测了司机与乘客的热舒适性问题,并与国外提供的热舒适范围作了比较,结果令人满意。显然,这一研究对进一步改进车室内环境的控制方法具有重要的指导意义。     

热障涂层热导率的研究进展

简要回顾了热障涂层体系的发展,讨论了氧化锆陶瓷材料的传热规律,包括涂层微观结构、陶瓷成分等因素的影响.同时指出了改进陶瓷涂层热导率的方法和开发适用于更高温度下的陶瓷涂层材料的指导原则,并详细介绍了改善热障涂层热导率的研究现状.     

Giant Thermal Rectification from Polyethylene Nanofiber Thermal Diodes

The realization of phononic computing is held hostage by the lack of high‐performance thermal devices. Here, it is shown through theoretical analysis and molecular dynamics simulations that unprecedented thermal rectification factors (as large as 1.20) can be achieved utilizing the phase‐dependent thermal conductivity of polyethylene nanofibers. More importantly, such high thermal rectifications only need very small temperature differences (<20 °C) across the device, which is a significant advantage over other thermal diodes which need temperature biases on the order of the operating temperature. Taking this into consideration, it is shown that the dimensionless temperature‐scaled rectification factors of the polymer nanofiber diodes range from 12 to 25—much larger than those of other thermal diodes (<8). The polymer nanofiber thermal diode consists of a crystalline portion whose thermal conductivity is highly phase‐sensitive and a cross‐linked portion which has a stable phase. Nanoscale size effect can be utilized to tune the phase transition temperature of the crystalline portion, enabling thermal diodes capable of operating at different temperatures. This work will be instrumental to the design of high performance, inexpensive, and easily processible thermal devices, based on which thermal circuits can be built to ultimately enable phononic computing.     

Anisotropic Thermal Diffusivities of Plasma-Sprayed Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are used to shield the blades of gas turbines from heat and wear. There is a pressing need to evaluate the thermal conductivity of TBCs in the thermal design of advanced gas turbines with high energy efficiency. These TBCs consist of a ceramic-based top coat and a bond coat on a superalloy substrate. Usually, the focus is on the thermal conductivity in the thickness direction of the TBC because heat tends to diffuse from the surface of the top coat to the substrate. However, the in-plane thermal conductivity is also important in the thermal design of gas turbines because the temperature distribution within the turbine cannot be ignored. Accordingly, a method is developed in this study for measuring the in-plane thermal diffusivity of the top coat. Yttria-stabilized zirconia top coats are prepared by thermal spraying under different conditions. The in-plane and cross-plane thermal diffusivities of the top coats are measured by the flash method to investigate the anisotropy of thermal conduction in a TBC. It is found that the in-plane thermal diffusivity is higher than the cross-plane one for each top coat and that the top coats have significantly anisotropic thermal diffusivity. The cross-sectional and in-plane microstructures of the top coats are observed, from which their porosities are evaluated. The thermal diffusivity and its anisotropy are discussed in detail in relation to microstructure and porosity.     

Characterization of Thermal Barrier Coatings Using Thermal Methods

Although low thermal conductivity was one of the major reasons for the development of thermal barrier coatings (TBCs) based on yttria stablilized zirconia (YSZ), its mechanical properties are often considered crucial in failure analysis and assessment of coatings. Thermal properties usually are treated as just basic material parameters and have not been utilized widely in TBC characterization and failure analysis. In fact, thermal transport properties such as thermal conductivity and thermal diffusivity are closely related to the microstructural changes of the TBC. In this paper, a brief overview of characterization of TBCs using thermal thermophysical properties and temperature mapping is presented.