Tree‑Inspired Structurally Graded Aerogel with Synergistic Water,Salt,and Thermal Transport for High‑Salinity Solar‑Powered Evaporation

Solar-powered interfacial evaporation is an energy-efficient solution for water scarcity.It requires solar absorbers to facilitate upward water transport and limit the heat to the surface for efficient evaporation.Furthermore,downward salt ion transport is also desired to prevent salt accumulation.However,achieving simultaneously fast water uptake,downward salt transport,and heat localization is challenging due to highly coupled water,mass,and thermal transport.Here,we develop a structurally graded aerogel inspired by tree transport systems to collectively optimize water,salt,and thermal transport.The arched aerogel features root-like,fan-shaped microchannels for rapid water uptake and downward salt diffusion,and horizontally aligned pores near the surface for heat localization through maximizing solar absorption and minimizing conductive heat loss.These structural characteristics gave rise to consistent evaporation rates of 2.09 kg m^(-2) h^(-1) under one-sun illumination in a 3.5 wt%NaCl solution for 7 days without degradation.Even in a high-salinity solution of 20 wt%NaCl,the evaporation rates maintained stable at 1.94 kg m^(-2) h^(-1) for 8 h without salt crystal formation.This work offers a novel microstructural design to address the complex interplay of water,salt,and thermal transport.

Effect of Fly Ash on Drying Shrinkage of Thermal Insulation Mortar with Glazed Hollow Beads

Drying shrinkage of thermal insulation mortar with glazed hollow beads was measured by a vertical length comparator, and the influences of fly ash with different contents（0, 18%, 36%, and 54% were used） on the long-term drying shrinkage were discussed. The mass loss was measured by the weighting method and the pore structure was characterized using three different methods, including the light microscopy, the mercury intrusion porosimetry（MIP）, and the nitrogen adsorption/desorption（NAD） experiments, and the correlations among them were researched. The results show that drying shrinkage process of thermal insulation mortar includes three steps with increasing curing time： the acceleration period（before 7 d）, the deceleration period（7-365 d）, and the metastable period（after 365 d）. Drying shrinkage in the first stage（7 d before） increases quickly owing to the fast water loss, and its development in the last two stages is attributed to the increment of the pore volume of mortar with the radius below 50 nm, especially the increment of the pore volume fraction of the pore radius within the size range between 7.3 nm and 12.3 nm. There is no change in the drying shrinkage development trend of mortar with fly ash addition, and three steps in the service life, but fly ash addition in the mortar restrains its value. There is a linear relationship between the drying shrinkage and fly ash content, which means that drying shrinkage reduces with fly ash addition.

Effect of electrodes and thermal insulators on grain refinement by electric current pulse

The application of electric current pulse（ECP） to a solidification process refers to the immersion of electrodes into the liquid metal and the employment of thermal insulators on the upper surface of metal.In order to ascertain the effects of these two factors on the structure refinement by the ECP technique,three groups of experiments were performed with different types of electrodes or various thermal insulators.By the comparison between solidification structures under different conditions,it is followed that the electrode and the thermal insulator have an obvious influence on the grain refinement under an applied ECP,and further analysis demonstrates that the thermal conditions of the liquid surface play a vital role in the modification of solidification structure.Also,the results support the viewpoint that most of the equiaxed grains originate from the liquid surface subjected to an ECP.

A lightweight and high compressive resistance thermal insulation material with dual-network structure

Ceramic fibrous aerogels are highly desirable for thermal management materials due to their high porosity,excellent elasticity,thermal conductivity,and good thermal resistance.However,the fabrication of nanofibrous aerogel with super-elasticity and good shape retention at the same time has remained challenging.To meet the requirements,a novel anisotropy nanofibrous-granular aerogel with a quasi-layered multi-arch-like and hierarchical-cellular structure is designed and prepared by vacuum-filtration-assisted freeze-drying and sintering.The quasi-layered multi-arch and flexible nanofibers endowed the aerogels with excellent mechanical robustness(ultimate stress up to 60 kPa with strain 60%)and super-elasticity with recoverable compression strain up to 60%.The introduced SiO_(2) aerogel nanoparticles and nanofibers are assembled into an arch-like structure and become the connection point of adjacent nanofibers,which endows low thermal conductivity(0.024 mW/(m·K))of composite aerogel.This novel strategy provides a fresh perspective for the preparation of nanofibrous aerogel with robust mechanical in thermal insulation and other fields.

Smart heat isolator with hollow multishelled structures

Safe, green and efficient industrial production has always been the pursuit of the chemical industry. Since thermal energy is the driving force for most of chemical reactions, an ideal reaction tank would have the capacity to automatically regulate heat conduction rate. In detail, this reaction tank should endow an ability that resists the heat loss when the reaction temperature is lower than the target, while accelerating the heat dissipation when the system is overheated. In this case, this smart reactor can not only minimize energy consumption but also reduce safety risks.Hollow structures are known to reduce heat conductivity. Particularly, the hollow structure with multishells can provide more interfaces and thus further inhibit heat transmission, which would be more favorable for heat isolation. Step forward, by coupling HoMSs with temperature-sensitive polymer, a smart heat isolation material has been fabricated in this work. It performs as a good heat isolator at a relatively lower temperature. A heat insulation effect of 6.5℃ can be achieved for the TSPU/3S–TiO_(2)HoMSs with a thickness of 1 mm under the temperature field of 50℃.The thermal conductivity of composite material would be raised under overheating conditions. Furthermore, this composite displays an unusual two-stage phase transformation during heating. Benefiting from the unique multishelled structure, energy is found to be gradually guided into the hollow structure and stored inside. This localized heat accumulation enables the composite to be a potential coating material for intelligent thermal-regulator and site-defined micro-reactor.

Mechanical properties and simulated thermal conductivity of biomimetic structured PS-PVD(Gd_(0.9)Yb_(0.1))_(2)Zr_(2)O_(7) thermal barrier coatings

Plasma spray physical vapor deposition(PS-PVD)(Gd_(0.9)Yb_(0.1))_(2)Zr_(2)O_(7)(GYbZ)thermal barrier coatings(TBCs)exhibited better silicate-phobicity than coatings produced by electron beam physical vapor depo-sition.In combination with PS-PVD and ultrafast laser direct writing technology,biomimetic structured GYbZ TBCs,with a triple-scale micro/nano surface microstructure,were obtained.Laser ablating on the PS-PVD GYbZ coating enhanced the surface roughness,improving its wear resistance without increasing the surface hardness.Furthermore,during the laser ablation processing,numerous nanoparticles were deposited in-situ in the gaps between columns of the coating,reducing the coating Young’s modulus.The simulated temperature field and heat flux field demonstrated that the presence of numerous interfaces between small columns of the PS-PVD coatings is beneficial to thermal insulation.However,laser ablation decreased the coating thickness,reducing the thermal insulation by around 20%-30%as compared to its PS-PVD counterpart,suggesting that a moderate increase in the coating thickness should be considered when designing an efficient TBC system.

Wood plastic composites based wood wall’s structure and thermal insulation performance

In order to solve the problem of poor thermal insulation in the current wood-plastic building,two kinds of structural wood wall integrated with wood plastic composite(WPC)are designed,and the thermal insulation performances of the walls are studied.The results show that the WPC integrated wall with frame-shear structure has a good stability,and the excellent performance of the WPC can be fully realized.Wall studs and wall panels are important factors affecting the thermal performance of the walls.Wood plastic materials can meet the thermal performance requirements of the walls.The single-layer frame walls and double-layer frame walls integrated with the WPC both have a good thermal performance.According to‘Design Standard for Energy Efficiency of Public Buildings(GB 50189-2015)’,the heat transfer coefficient of the single-layer frame wall integrated with 20 mm thick WPC wall boards and WPC wall studs is 0.414 W/(m^(2)•K),which can meet the standard of wall thermal levelⅡt and is suitable for cold areas.The heat transfer coefficient of the double-layer frame wall integrated with 50 mm thick WPC wall panel and WPC wall studs is 0.207 W/(m^(2)•K),which can meet the standard of wall thermal levelⅠt and is suitable for severe cold areas.

Design,Preparation and Properties of Bio-inspired Hierarchical Structure Yarns with Enhanced Thermal Insulation and Water Transfer Ability

Encouraged by the porous and stable structure of cold-resist animals’hair or feather,bio-inspired hierarchical structure yarns combining polyacrylonitrile(PAN)nanofibers and polypropylene(PP)hollow microfibers have been developed by a modified conjugate electrospinning technology.Physical cross-linking has been built to increase fibers adhesion and construct interlayer support for nanofibrous assembly.The nanofibers and hollow microfibers construct a stable porous structure with porosity of 62%,providing excellent thermal insulating ability[temperature difference(|ΔT|)between skin and yarn surface is 4.9℃]as well as good mechanical property.More interestingly,the water transfer ability(infiltrate the yarn in 10 s)of synthetic fibers has been improved greatly by the combination of thin diameter nanofibers to the yarn.It is believed that the research lays the foundation for bio-inspired engineering technology in the manufacture of thermal comfort.

Multifunctional cellular carbon foams derived from chitosan toward self-cleaning, thermal insulation, and highly efficient microwave absorption properties

To adapt the practical demand,designing and constructing the multifunctional microwave absorbers(MAs)is the key future direction of research and development.However,effective integrating the multiple functions into a single material remains a huge challenge.Herein,cellular carbon foams(CCFs)with different porous structures were elaborately designed and fabricated in high efficiency through a facile continuous freeze-drying and carbonization processes using a sustainable biomass chitosan as the precursor.The obtained results revealed that the thermal treated temperature and g-C_(3)N_(4) amount played a great impact on the carbonization degrees,pore sizes,and morphologies of CCFs,which led to their tunable electromagnetic(EM)parameters,improved conduction loss,and polarization loss abilities.Owing to the special cellular structure,the designed CCFs samples simultaneously displayed the strong absorption capabilities,broad absorption bandwidths,and thin matching thicknesses.Meanwhile,the as-prepared CCFs exhibited the strong hydrophobicity and good thermal insulation,endowing its attractive functions of self-cleaning and thermal insulation.Therefore,our findings not only presented a facile approach to produce different porous structures of CCFs,but also provided an effective strategy to develop multifunctional high-performance MAs on basis of three-dimensional CCFs.

Hierarchical porous(Ta_(0.2)Nb_(0.2)Ti_(0.2)Zr_(0.2)Hf_(0.2))C high-entropy ceramics prepared by a self-foaming method for thermal insulation

To meet the emerging demands for thermal protection materials for hypersonic aircraft,developing porous ultrahigh-temperature ceramics with both robust mechanical properties and superior thermal insulation performance is a critical challenge.Herein,we report novel porous(Ta_(0.2)Nb_(0.2)Ti_(0.2)Zr_(0.2)Hf_(0.2))C high-entropy carbide(PHEC)ceramics fabricated by a self-foaming method using commercially available metal chloride and furfuryl alcohol(FA)as precursors.The PHEC ceramics are constructed of microspheres with a size of 2µm,leading to a high porosity of 91.3%and an interconnected frame.These microspheres consist of high-entropy carbide grains(20 nm),resulting in abundant interfaces and nanosized pores in the PHEC ceramics.Due to its unique hierarchical structure,the prepared PHEC ceramics have outstanding compressive strength(28.1±2 MPa)and exceptionally low thermal conductivity(κ_(T),0.046 W·m^(-1)·K^(-1))at room temperature.This makes it a promising thermal insulation materials for ultrahigh temperature applications.This work provides a cost-effective and facile strategy for producing porous ultrahigh-temperature ceramics.

High-stability temperature control and frequency-domain analysis of sandwich-like insulation design based on phase change materials for satellite thermal management

High-stability thermal management is critical for the measurements of high sensitivity for temperature, but also challenging because any small thermal disturbances could lead to unacceptable temperature fluctuations. The present work delivers a design for passive temperature control, customized for a component in the satellites for gravitational wave detection. A novel sandwichlike structure is proposed with the configurations of proper materials, consisting of a layer of insulation material and two layers of nanocomposite phase change materials, bringing an integration of heat insulation and absorption/storage. Its performance is examined using an improved thermal network model and the revised transfer function method(TFM). The basic results of the two methods are validated by present COMSOL simulations and available numerical and experimental data in the literature. An effective reduction of temperature fluctuation is achieved to the scale of 0.1 K, even under two thermal disturbances from different directions: a radiative heat flux of 20 W m~(-2)(inside) and a temperature fluctuation of about 20 K(outside). Moreover,the TFM is employed to analyze the effects of the frequency of thermal disturbance: excellent damping performance is obtained for over 3.2 mHz and the underlying mechanism is discussed. Overall, the present design is expected to be combined with active temperature control to explore more possible ways for temperature control with higher stability.

膨胀型钢结构防火涂层隔热性能的研究进展

隔热性能的准确量化是防火涂层厚度设计的关键。膨胀型钢结构防火涂层的隔热性能在高温下受升温速率的影响,投入使用后其隔热性能会发生退化,这些特点给膨胀型钢结构防火涂层的厚度设计提出了挑战。总结了膨胀型钢结构防火涂层隔热性能的定量表征方法,分析了隔热性能的影响因素以及这些因素的作用机理和规律,提出了膨胀型钢结构防火涂层厚度设计涉及的关键科学问题及解决方法。

BN-石墨烯-BN夹层式结构的ABS基复合材料导热绝缘性能

为解决石墨烯/ABS复合材料导热不绝缘,采用夹层式结构制备ABS基导热绝缘材料。通过混炼分别得到石墨烯/ABS、六方氮化硼(hBN)/ABS复合材料,再将hBN/ABS对石墨烯/ABS进行包覆,得到了hBN/ABS—石墨烯/ABS—hBN/ABS夹层式结构的导热绝缘材料。研究了石墨烯含量和夹层厚度对ABS基导热绝缘材料标准试样的热导率、电阻率的影响,发现,包覆了hBN/ABS绝缘层后的夹层式结构试样,石墨烯填料对导热性能的提升作用幅度减小,此时,材料受氮化硼/ABS绝缘层热传导的影响较大,与改性前的ABS相比,复合材料导热性能得到较大的改善,同时,复合材料阻值达1×1010数量级,成为绝缘体。

三明治式飞行器热防护结构研究进展

三明治式先进热防护结构广泛应用于航空航天装备。然而,由于上述结构多为板面与芯体组合形式,加之通道内流场的综合作用,其换热机理呈现出复杂、多变及强耦合的特点,难以针对真实结构及环境工况开展计算、仿真及实验工作。为此,致力于为飞行器热防护结构设计、仿真、试验、优化工作提供可靠技术支撑,本文选取蜂窝夹芯结构、波纹板夹芯结构和点阵夹芯结构,对于点阵夹芯结构又从四面体、金字塔、X型和Kagome型点阵着手,对国际、国内主要研究团队近年来相关流动与换热研究成果进行综述。阐述了3种热防护结构的结构形式和发展历程,分析了板面与芯体组合作用下的换热形式及隔热机理,归纳总结了现有研究不足之处与发展趋势。可以看出,点阵夹芯相比蜂窝与波纹板夹芯结构,由于其芯体内复杂湍流的存在,换热效率高、温度梯度小,具有更好的隔热潜力。

内/外隔热复合结构炸药装药快速烤燃热防护效应

为了研究快速烤燃(火烧)条件下炸药装药内/外隔热复合结构(内隔热材料/外阻燃材料)的热防护效应,对多种内/外隔热复合结构的炸药装药进行多点测温快速烤燃试验,得到火焰场和炸药装药各测点的温度-时间曲线及装药点火响应时间。开展内/外隔热复合结构炸药装药快速烤燃数值模拟,获得内/外隔热复合结构对装药快速烤燃点火响应时间的影响规律。研究结果表明:在快速烤燃过程中,外阻燃材料由于火烧变性存在导热增强及隔热减弱效应,在数值模拟中需考虑该效应;无论使用单独的隔热/阻燃材料还是使用内/外隔热复合结构,炸药装药的点火响应时间均随着材料涂覆厚度增加而延后,其中内/外隔热复合结构具有更好的热防护能力;点火位置均发生在装药端面棱角处,装药点火后反应烈度不受内/外隔热复合结构影响,反应等级均为爆燃;对于一定热防护性能范围内的隔热阻燃材料,壳体外表面涂层材料是耐高温纳米隔热材料、壳体内表面涂层材料是高效隔热防护材料时复合结构的隔热效果最好,并且当需求的隔热效果给定时,可考虑优先增加壳体外表面涂层的涂覆厚度,实现以最小涂覆厚度的内/外隔热复合结构满足所需的隔热效果。研究成果可为提升弹药热安全性设计提供参考。

相变石膏板围护结构隔热应用实验研究

为研究相变石膏板围护结构在过渡季节的储热性能,搭建了两间尺寸相同的实验对比房,将相变石膏板贴敷于围护结构内侧,测试对多种工况下实验对比房的室内温度及壁面温度,通过房间热性能分析探讨其在过渡季节的适用性。石膏板中的相变微胶囊以石蜡(正十八烷)为芯材,聚甲基丙烯酸甲酯(Polymethyl methacrylate,PMMA)为壁材,相变温度28℃,相变潜热180 kJ/kg。在相同的室外气候条件下,进行一个月的多组工况实验研究,测试了室内空气温度和墙体表面温度的变化规律,并与普通房间进行了室内热环境对比分析。结果表明:相变石膏板热性能稳定;在杭州地区过渡季节最高可降低室内峰值温度1.10℃,减缓壁面温度波动1.18℃,延迟峰值时间40 min,降低室内温度不舒适度6.82℃·h/d,有效缓解了室内的温度波动,增强了围护结构的热惰性。此外,与夜间自然通风相比,相变围护结构在夜间通风的情况下可以减少室内不舒适度时间约2 h,减少累计室内温度不舒适度2.08℃·h/d,有效提高室内热舒适性。该研究通过对比实验验证了相变石膏板应用于围护结构的隔热效果,可为后续模拟研究提供参考。

对流-导热耦合作用下保温层对寒区水工隧洞衬砌结构力学特性的影响

以新疆布伦口水电站引水隧洞为例,考虑对流-导热作用,通过现场监测成果和有限元仿真计算,分析引水隧洞在不同位置铺设不同厚度的保温层对衬砌结构热-力耦合特性的影响。结果表明,表面铺设时,保温层厚度与衬砌的冻胀力呈负相关,且当厚度在0.06 m以上时,二次衬砌的冻胀力变为压应力;保温层厚度与衬砌的横向位移呈正相关,与纵向位移呈负相关。夹层铺设时,保温层厚度与二次衬砌的冻胀力呈正相关,与一次衬砌的冻胀力呈负相关;随着保温层厚度的增加,二次衬砌的最大主应力变为拉应力,不利于二次衬砌的安全稳定;随着保温层厚度的增加,一次、二次衬砌的横向位移差值增大近4倍,纵向位移差值增大10倍以上。

二氧化硅气凝胶原位填充聚酰亚胺泡沫的结构及隔热性能研究

以超轻质开孔柔性聚酰亚胺泡沫为基体,采用溶胶凝胶工艺制备了一系列二氧化硅气凝胶原位填充的聚酰亚胺复合泡沫。复合泡沫密度10~100 kg/m^(3)可调,厚度1~400 mm可调,最大宏观尺寸可达1m×1m。对其泡孔结构、隔热性能、热性能进行了系统表征,分析了二氧化硅气凝胶原位填充聚酰亚胺泡沫的隔热机理。结果表明:二氧化硅气凝胶的引入,可有效降低复合泡沫室温热导率,提高其隔热性能;随着二氧化硅气凝胶含量的增加,聚酰亚胺复合泡沫的热导率由38.8 mW/(m·K)降低至19.6 mW/(m·K);热端温度300℃时,复合泡沫热导率仅为61.1 mW/(m·K);填充二氧化硅气凝胶后,聚酰亚胺复合泡沫热稳定性大大提高,在900℃下热失重残留量约为80%。

基于不同接箍形式的隔热油管传热特性模拟分析

热力采油方法是稠油开采的主要方式之一,在注蒸汽热采过程中,隔热油管可以有效减少井筒径向传热损失;常规隔热油管使用一段时间后,热损失明显增加,如何改进隔热油管结构,降低注汽过程热损失,需要进一步研究。基于常规隔热油管,提出了2种改进隔热油管结构:接箍处含隔热衬套油管和直连式隔热油管;在对3种隔热油管物理结构分析基础上,建立了热损分析模型,根据所建模型,利用COMSOL软件进行了模拟计算分析,给出了3种隔热油管结构的温度分布和热损失变化特性,并进行了对比分析。结果表明:接箍处含隔热衬套油管热损失最小,直连式隔热油管热损失适中,建议对普通隔热油管接箍采取保温措施。本研究为注蒸汽热采过程减少热损失、提高稠油采收效果提供一定支撑。

防寒服开口设计对其保暖性能的影响研究

为探究开口设计对防寒服隔热性能的影响程度,文章对门襟、袖口及领口三个主要的服装开口进行排列组合,通过暖体假人实验探究不同环境温度下、不同开口设计对防寒服隔热性能的影响。结果表明:三种开口的优化设计均对防寒服总热阻有显著影响(p<0.05),其影响程度为领口>袖口>门襟,同时温度会影响三种开口设计对服装隔热性能的提升效果;5℃时服装总热阻最大提升率达7.20%,-10℃时同款防寒服总热阻仅提升5.27%。门襟设计对上臂、下胸及后腰部位的服装隔热性能提升明显,局部服装热阻变化率达6%;环境温度5℃下袖口束紧设计可将手部及下臂部位的服装局部热阻提升7.00%;领口束紧设计可将下胸、腹部、后背、后腰部位的服装局部热阻提升10.00%。研究结果可为防寒服的开口结构设计提供量化的依据和参考。