Measurement of thermal conductivity of materials using single-side TPS technique

Based on the traditional measurement theory of transient plane source (TPS) technique, single-side TPS method is proposed for measuring the thermal conductivity of single specimen. The problem of transient heat conduction in a semi-infinite boundary condition is studied and the theoretical formula of single-side TPS method is deduced. During the measurement, the influence of the probe heat capacity on the results is analyzed and the corresponding mathematical compensation model is established, and a series of experiments on different materials are conducted by hot disk probe at normal temperature and pressure. The results show that the relative error with the single-side TPS method is less than 5% and the relative standard deviation is no greater than 3%. This method has high accuracy and good reproducibility, which provides a feasible measuring method for single material that does not meet the requirements of the standard TPS theory.

Laboratory and field experiment on measurement of soil thermal conductivity by probe method

The authors presented a new measuring method of the soil thermal conductivity,the probe method,which is designed and made based on the theory of line heat source. This method is used to measure thermal conductivity of coarse sand,fine sand and silty clay in different water contents. The results that measured by the probe method are well consistent with those of QTM-D_2. The soil thermal conductivity increases in different levels with the increase of the water content. Compared the soil thermal conductivity measured by the probe method in laboratory with in-situ experiment,it shows that the measuring gap gradually increases with the increase of the depth. The reason is that the in-situ measuring thermal conductivity can reflect the actual situation of the soil mass.

Quantitative analysis on influencing factors for interface propagation-based thermal conductivity measurement method during solid-liquid transition

The recently proposed interface propagation-based method has shown its advantages in obtaining the thermal conductivity of phase change materials during solid-liquid transition over conventional techniques. However, in previous investigation, the analysis on the measurement error was qualitative and only focused on the total effects on the measurement without decoupling the influencing factors. This paper discusses the effects of influencing factors on the measurement results for the interface propagation-based method. Numerical simulations were performed to explore the influencing factors, namely model simplification, subcooling and natural convection, along with their impact on the measurement process and corresponding measurement results. The numerical solutions were provided in terms of moving curves of the solid-liquid interface and the predicted values of thermal conductivity. Results indicated that the impact of simplified model was strongly dependent on Stefan number of the melting process. The degree of subcooling would lead to underestimated values for thermal conductivity prediction. The natural convection would intensify the heat transfer rate in the liquid region, thereby overestimating the obtained results of thermal conductivity. Correlations and experimental guidelines are provided. The relative errors are limited in ±1.5%,±3%and ±2% corresponding to the impact of simplified model, subcooling and natural convection, respectively.

Hierarchical graphite foil/CoNi2S4 flexible electrode with superior thermal conductivity for high-performance supercapacitors

Effective heat dissipation is a crucial issue in electrochemical energy storage devices. Thus, it is highly desirable to develop high-performance electrode materials with high thermal conductivity. Here, we report a facile one-step electrodeposition method to synthesize ternary cobalt nickel sulfide（CoNi2S4）flower-like nanosheets which are grown on graphite foil（GF） as binder-free electrode materials for supercapacitors. The as-fabricated GF/CoNi2S4 integrated electrode manifested an excellent thermal conductivity of 620.1 W·m-1·K-1 and a high specific capacitance of 881 F·g-2 at 5 mA cm-2, as well as good rate capability and cycling stability. Ultimately, the all-solid-state symmetric supercapacitor based on these advanced electrodes demonstrated superior heat dissipation performance during the galvanostatic charge-discharge processes. This novel strategy provides a new example of effective thermal management for potential applications in energy storage devices.

Research of Mechanical and Thermal Properties of Composite Material Based on Gypsum and Straw

This article is focused on the investigation of the mechanical and thermal properties of composite material that could be used for the production of plaster or plasterboards.This composite material is made of gypsum and reinforcing natural fibers.The article verifies whether this natural reinforcement can improve the investigated properties compared to conventional plasters and gypsum plasterboards made of pure gypsum.From this composite material,high-strength plasterboards could then be produced,which meet the higher demands of users than conventional gypsum plasterboards.For their production,natural waste materials would be used efficiently.As part of the development of new building materials,it is necessary to specify essential characteristics for their later use in civil engineering.Crushed wheat straw and three gypsum classes with strengths G2(2 MPa)—gypsum Class I.,G5(5 MPa)—gypsum Class II.and G16(16 MPa)—gypsum Class III.were used to create the test samples.Samples were made with different ratios of the two ingredients,with the percentages of straw being 0%,2.5%,and 5%for each gypsum grade.The first part of the article describes how the increasing proportion of straw affects the composite’s mechanical properties(flexural strength and compressive strength).The second part of the article focuses on the change of thermal properties(thermal conductivity and specific heat capacity).The last part of the article mentions the verification of the fire properties(single-flame source fire test and gross heat of combustion)of this composite material.The research has shown that the increasing proportion of straw reinforcement caused a deterioration in the flexural strength(up to 56.49%in the 3.series of gypsum Class II.)and compressive strength(up to 80.27%in the 3.series of gypsum Class III.)and an improvement in the specific heat capacity and thermal conductivity(up to 31.40%in the 3.series).This composite material is thus not suitable for the production of high-strength plasterboards,but its reduced mechanical properties do not prevent its use for interior plasters.Based on the performed fire tests,it can be said that this composite material can be classified as a non-flammable material of reaction to fire Classes A1 or A2.From an ecological point of view,it is advantageous to use a composite material with a higher straw content.

Research for Optimizing Porosity of Porous Thermal-insulating Materials

With the energy crisis and ecological environment deterioration, porous thermal-insulating materials become an advanced research hotspot, and the influence of pore distribution cannot be ignored. The mathematical model is established basing on the heat transfor theory, regarding the minimum heat flux density as the objective function, the constant total porosity as a constraint condition, using the BFGS method to optimize the pore distribution. The results show that when the heat flux is the minimum, in the case of the fixed total porosity, the high temperature zone has high porosity, the low temperature zone has low porosity; the maximal fluctuating amplitude of porosity between the adjacent discrete points has great impact on the thermal insulating performanee, the greater the fluctuating amplitude, the better the thermal insulating ability. After calculating the temperature field of the corresponding physical model, it can be found that the temperature gradient is non-uniform, the temperature gradient of the high temperature zone is steep, and that of the low temperature zone is gentle. These results have guiding significance for preparation of porous thermal-insulating materials.

Study of the Thermal Characteristics of a Geomaterial:Case of SavèGranites in the Republic of Benin

This work focuses on the valorization of local materials.The rock that is granite,a material used in construction thanks to its mechanical resistance,is the subject of our study.The granite of the commune of Savè,made it possible to appreciate the thermal behavior of this rock studied with a view to its use as a building material.To this end,a thermal diffusivity measurement test was carried out on this material.Thus,we made samples which were then connected to a data acquisition box via thermocouples.A Python script is used to ensure the collection of temperature values over time.From this thermal diffusivity test carried out on the granite taken from the Savèbreasts,we obtained an average diffusivity a=5.84×10^(-6)m^(2)/s.As a result,the thermal effusivity and the heat capacity of the material were determined having respectively the value 1,351.09 J/(K·m^(2)·s^(1/2))and 547,945.21 J/(m^(3)·K).These different results highlight a thermal characterization of Savègranites as a relevant material in the design and construction of an energy-efficient eco-housing.

Design,progress and challenges of 3D carbon-based thermally conductive networks

The advent of the 5G era has stimulated the rapid development of high power electronics with dense integration.Three-dimensional(3D)thermally conductive networks,possessing high thermal and electrical conductivities and many different structures,are regarded as key materials to improve the performance of electronic devices.We provide a critical overview of carbonbased 3D thermally conductive networks,emphasizing their preparation-structure-property relationships and their applications in different scenarios.A detailed discussion of the microscopic principles of thermal conductivity is provided,which is crucial for increasing it.This is followed by an in-depth account of the construction of 3D networks using different carbon materials,such as graphene,carbon foam,and carbon nanotubes.Techniques for the assembly of two-dimensional graphene into 3D networks and their effects on thermal conductivity are emphasized.Finally,the existing challenges and future prospects for 3D carbon-based thermally conductive networks are discussed.

Fabrication, microstructure and properties of SiCp/Cu heat sink materials

Cu-coated powder was fabricated by electroless plating process, and the composition and morphology of coated powder were studied. Moreover, Cu-30, 40, 50 vol.%SiCp heat sink materials were fabricated by hot pressing using coated and uncoated powder. And the microstructure and thermophysical properties of the heat sink materials were also studied. The results show that SiCp particles distribute uniformly in heat sink materials and the interface between SiCp particles and Cu matrix is clear and well bonded. On the condition of same volume fraction of SiCp, the thermal conductivity of the material using coated powder is larger than that of the material using uncoated powder. Under experiment conditions, the thermal conductivity and coefficient of thermal expansion of Cu-30 vol.%SiCp heat sink material is 236.2 W·m-1·K-1 and 9.9×10-6/K (30-200 ℃) respectively. It provides important reference data for future experiments.

A non-destructive method to measure the thermal properties of frozen soils during phase transition

Frozen soils cover about 40% of the land surface on the earth and are responsible for the global energybalances affecting the climate. Measurement of the thermal properties of frozen soils during phasetransition is important for analyzing the thermal transport process. Due to the involvement of phasetransition, the thermal properties of frozen soils are rather complex. This paper introduces the uses of amultifunctional instrument that integrates time domain reflectometry （TDR） sensor and thermal pulsetechnology （TPT） to measure the thermal properties of soil during phase transition. With this method,the extent of phase transition （freezing/thawing） was measured with the TDR module; and the correspondingthermal properties were measured with the TPT module. Therefore, the variation of thermalproperties with the extent of freezing/thawing can be obtained. Wet soils were used to demonstrate theperformance of this measurement method. The performance of individual modules was first validatedwith designed experiments. The new sensor was then used to monitor the properties of soils duringfreezingethawing process, from which the freezing/thawing degree and thermal properties weresimultaneously measured. The results are consistent with documented trends of thermal propertiesvariations. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Experimental investigation on the effective thermal conductivities of different hydrate-bearing sediments

The natural gas hydrate has been regarded as an important future green energy.Significant progress on the hydrate exploitation has been made,but some challenges are still remaining.In order to enhance the hydrate exploitation efficiency,a significant understanding of the effective thermal conductivity(ETC)of the hydrate-bearing sediment has become essential,since it directly controls the heat and mass transfer behaviors,and thereby determines the stability of hydrate reservoir and production rate.In this study,the effective thermal conductivities of various hydrate-bearing sediments were in-situ measured and studied.The impacts of temperature,particle size and type of sediment were investigated.The effective thermal conductivities of the quartz sand sediments before and after hydrate formation were in-situ measured.The results show the weak negative correlation of effective thermal conductivity of the quartz sand sediment on the temperature before and after the hydrate formation.The effective thermal conductivity of the hydrate-bearing sediment decreases with the increase of particle size of the sediment.The dominant effect of the type of porous medium on the characteristics of the effective thermal conductivity of hydrate-bearing sediment was highlighted.The results indicate that both the effective thermal conductivities of hydrate-bearing quartz sand sediment and hydrate-bearing silicon carbide sediment are weakly negatively correlated with temperature,but the effective thermal conductivity of hydrate-bearing clay sediment is weakly positively dependent on the temperature.In addition,the values of the effective thermal conductivities of various hydrate-bearing sediments are in the order of hydrate-bearing silicon carbide sediment>hydrate-bearing quartz sand sediment>hydrate-bearing clay sediment.These findings could suggest that the intrinsic thermal conductivity of porous medium could control the characteristics of effective thermal conductivity of hydrate-bearing sediment.

Thermal Response Test by Improved Test Rig with Heating or Cooling Soil

An improved test rig providing both the heat and cold source was used to perform thermal response test （TRT）, and the line source model was used for data analysis. The principle of determining the temperature difference between the inlet and outlet of test well can keep the heating or cooling rate constant, along with a reduced size of test rig. Among the influencial factors of the line source model, the temperature difference was determined as the most important, which agreed with the test results. When the gravel was taken as the backfill material, the soil thermal conductivities of heating and cooling at the test place were 1.883 W/（m＆#183;K） and 1.754 W/（m＆#183;K）, respectively, and the deviation of TRT between heating and cooling soil was 6.8%. In the case of fine sand, the thermal conductivities of heating and cooling were 1.541 W/（m＆#183;K） and 1.486 W/（m＆#183;K）, respectively, and the corresponding deviation was 6%. It was also concluded that different velocities of water had less influence on TRT than the temperature difference.

A New Type of Paper-frame Cavernous Material and Its Application in Energy Efficiency in Buildings

This paper introduces a new type of paper-frame cavernous material, which is a made-up hollow material, by using silicate-cinder size to drench and daub. It possesses excellent performances such as light-weight, high-intensity, fire-resistance, sound-insulation, heat-insulation and no-pollution. Composed with concrete materials, a new type of bearing and energy-efficient block can be gained, which is kind of excellent wall materials and has a wide application prospect.

Sr含量对Al-Si合金显微组织和热导率的影响

以纯铝、Al-20Si和Al-10Sr中间合金为原料,Sr为变质剂(含量为0.01%、0.02%、0.04%和0.06%,质量分数),制备了Al-7Si-xSr、Al-12Si-xSr和Al-20Si-xSr合金,研究了Sr含量对Al-Si合金相变储热材料显微组织及热导率的影响。利用Hot Disk热常数分析仪测量合金的热导率,通过扫描电镜观察及分析合金的显微组织。结果表明:在Al-Si合金中添加变质元素Sr会影响合金的热导率,Al-7Si-0.04Sr合金热导率较Al-7Si合金增加了73.47 W·m^(-1)·K^(-1),Al-20Si-0.04Sr合金的热导率较Al-20Si合金增加了24.09 W·m^(-1)·K^(-1),Al-12Si-0.04Sr合金的热导率较Al-12Si合金增加了17.79 W·m^(-1)·K^(-1)。铝硅合金热导率的增长主要与α(Al)、共晶硅和初晶硅的形貌有关。经过Sr变质之后,Al-7Si合金中共晶Si立体形貌均由片层状转变为珊瑚状,Al-12Si和Al-20Si合金中共晶Si立体形貌由片层状转变为枝条状;其中,Al-7Si合金中α(Al)尺寸明显减少、排列紧密,二次枝晶臂间距逐渐减小;Al-20Si合金中的初晶Si尺寸明显减小,其形貌由多角的大块状变为小块状;α(Al)形态的转变不仅能够为自由电子的传输提供快速通道,而且还会使得共晶Si的排列更加规则,减少自由电子发生散射的几率,对合金的热导率影响较大。共晶Si由片层状转变为珊瑚状或枝条状,增加电子的平均自由程,有利于电子的传输。Al-20Si合金的热导率与初晶Si的形态有着重要联系,大尺寸且形状完整的初晶Si会发生晶格振动,会提高合金的热导率。

基于LBM的低导热材料板强化沸腾换热机理分析

为进一步强化沸腾换热,通过在固体加热器的上壁面附近嵌入多段低导热材料板,实现了沸腾换热的受热面上的温度随空间的交替变化。采用单组分多相LBM,考察了低导热材料板的数量和间隙间距对沸腾换热性能和气泡动力学的影响,从微观角度揭示了添加低导热材料板强化沸腾换热的机理。结果表明:气泡动态行为随间隙间距的增大而发生变化,会出现气泡合并、独立生长等气泡脱离过程。结合气泡动态行为、温度场和流场分析,发现气泡首先会在间隙受热面处成核生长,脱离气泡的涡流可以促进生长气泡在受热面的横向迁移和合并过程,在一定间隙间距范围,气泡会相互融合形成较大的液桥,液桥的存在能够促进受热面气泡根部周围微层的蒸发,推动了间隙受热面处的冷流体再润湿过程。添加多段低导热材料板,间隙处热量积聚、气泡合并形成液桥、间隙受热面的再润湿、气泡横向迁移和多气泡的快速合并等这些过程的共同作用强化了沸腾换热性能。

真空绝热板芯材的研究进展与展望

随着我国经济的迅速发展和人们对生活水平的要求越来越高,节能减排对实现“碳达峰”和“碳中和”的目标显得越来越重要。真空绝热板(vacuum insolation panels,VIP)是一种新型的高效保温隔热材料,其中,芯材作为VIP的核心和骨架结构,不仅承担着支撑作用,而且是板内热量传递的主要通道,对保证VIP的保温性能具有关键作用。基于此,本文首先重点介绍了真空绝热板在绿色建筑和冷链物流领域应用的意义,明确了目前制约真空绝热板领域发展的关键问题;随后综述了真空绝热板芯材的研究现状和进展,比对了不同种类芯材(颗粒类芯材、泡沫类芯材、纤维类芯材、生物质材料类芯材和复合类芯材)在原料来源、保温性能、生产工艺及环境保护方面的优劣,将绿色、可再生的生物质基材料用作真空绝热板芯材进行了对比探讨;最后对真空绝热板芯材未来的研究方向和发展前景进行了总结和展望。本文指出,传统以玻璃纤维、有机泡沫或者气相二氧化硅为芯材的真空绝热板,存在生产成本高、不可再生、难降解、污染环境等问题,所以通过功能化手段获得新型、绿色、低成本、具有良好微观孔隙结构和高热阻的芯材是制约真空绝热板发展的关键。生物质材料具有来源广泛、成本低廉、绿色环保、孔隙结构丰富等优点,是一种极具潜力的VIP芯材原料,也将是真空绝热板芯材的重要研究方向。因此,生物质基芯材真空绝热板未来的发展还需进一步拓宽其原料来源、改善制备方法和工艺、明确老化和使役性能、关注复合芯材的开发,不断提高VIP的性能,扩展其应用领域。

基于激光热成像的薄膜面向导热系数测试方法

提出一种基于激光热成像的薄膜面向导热系数测试方法。仿真论证了激光加热相较于常规电加热方案的热损失差异;分析了激光加热功率、表面换热系数、测温模型增益系数等关键参数标定问题,并设计了相应的方案。基于15个不同材料或厚度的薄膜和薄片样品进行了实验,测试结果和参考值相对偏差均<6%,其中导热系数<3 W/(m·K)的样品测试误差显著优于常规方法,这表明该方法可有效改善热流环路积分法对低导热薄膜的测试精度。

生物质多孔碳复合相变材料制备和热性能研究

将木材通过高温碳化的方法制备三维生物质碳基材料用于相变材料载体,制备复合相变材料,并对复合相变材料进行结构表征、性能测试及防泄漏实验。结果表明:多孔碳载体材料导热孔道网络完整,保证了有机相变材料的高效稳定负载量;相比于纯相变材料,70%PA@GNS热导系数达到了0.763W/(m·K),提高了3.18倍;含有20%多孔碳复合材料的潜热值达到了182J/g,比理论值潜热值高了约7%;并能有效防止相变材料泄漏。

聚三唑树脂/氮化硼纳米片复合材料的制备与性能

采用六方氮化硼(h-BN)、蔗糖和尿素以干法球磨的方式高产率制备了氨基和羟基功能化的氮化硼纳米片(BNNS-AH),对BNNS-AH进行了详细的表征,制备的BNNS-AH的厚度为1.5 nm,层数为4~6,平均直径约为1.5μm,产率可达91.0%,在水中稳定的分散液浓度可达30 mg/mL。然后以共混的方法制备了聚三唑树脂/氮化硼纳米片复合材料(PTA树脂/BNNS-AH复合材料),并研究了BNNS-AH的添加量对PTA树脂/BNNS-AH复合材料热性能的影响。结果表明:与PTA纯树脂相比,复合材料的玻璃化转变温度(T_(g))、质量失重5%时的温度(T_(d5))、导热系数均有明显提升,其中当BNNS-AH质量分数为3.0%时,复合材料的T_(g)达到243℃,提高了32℃;T_(d5)达到362℃,提高了19℃;导热系数为0.33 W·m^(-1)·K^(-1),提高了64.5%。

多孔金属泡沫强化石蜡相变蓄热性能

针对石蜡(PW)相变材料热导率低和易泄漏的问题,采用“冰模板法”制备多孔金属泡沫铝作为支撑骨架,通过“真空浸渍法”将石蜡渗入金属泡沫铝的多孔结构中,制得化学性质稳定的相变复合材料(PCC),并对其形貌结构、防泄漏性能、热循环稳定性、热响应性能和热导率进行测试。结果表明,随着铝骨架比例的增加,泄漏情况随之减弱,有效提高了PCC的防泄漏性能。在此基础上对其热物性进行研究,金属泡沫的引入并未影响PW的相变温度,PCC的熔化和凝固峰值分别稳定在61℃和51℃。然而随着铝骨架比例的增加,PCC的相变焓值呈现下降趋势。经50次相变循环后,PCC的熔化和凝固焓值均基本保持稳定,其中PW@30Al样品的熔化和凝固焓值分别维持在116 J/g和118 J/g,表现出良好的热循环稳定性和相变可逆性。此外,随着铝骨架比例的增加,PCC的导热性能逐渐提高、热响应速度更快,其中PW@30Al样品的热导率由PW的0.2 W/(m·K)增加至3.1 W/(m·K),提高了约15倍,在相变蓄热和热管理等领域具有广泛的应用前景。