Influence of thermal insulation layer schemes on the frost heaving force in tunnels

In extreme cold regions,a thermal insulation layer(TIL)is commonly employed to mitigate the detrimental effects of frost heaving forces in tunnels.Optimizing the laying scheme of TIL,specifically minimizing frost heaving forces,holds considerable importance in the prevention of frost damage.This research developed a two-dimensional unsteady temperature field of circular tunnels by using the difference method(taking the off-wall laying method as an example)based on the law of conservation of energy.Then,the frozen circle and water migration coefficient were introduced to establish the relationship between the temperature field and frost heaving forces,and a reliable methodology for calculating these forces under the specific conditions of TIL installation was developed.Then(i)the influence of the air layer thickness of the off-wall laying method,(ii)different laying methods of TIL,(iii)the TIL thickness,(iv)the thermal conductivity of the TIL,and(v)the freeze-thaw cycles on the frost heaving force were investigated.The results showed that the frost heaving force served as a reliable and effective metric for evaluating the insulation effect in tunnels.In order to avoid frost damage in compliance with the design requirements,the insulation effects from various laying methods were established,in descending efficacy order as follows:off-wall laying,double layer laying,surface laying,and sandwich laying.Our findings revealed that the optimal thickness for the air layer in the offwall laying method was 0.10 m.The insulation effect of materials with a thermal conductivity below 0.047 W/(m·℃)was furthermore found to be good.Under freeze-thaw cycle conditions,it is concluded that to prevent frost damage,the TIL thickness should be the sum of the thickness r1 of the first freeze-thaw cycle without frost heaving forces and an additional reserve value 0.06r1 of the TIL thickness.

A layered multifunctional framework based on polyacrylonitrile and MOF derivatives for stable lithium metal anode

Composite Li metal anodes based on three-dimensional(3D) porous frameworks have been considered as an effective material for achieving stable Li metal batteries with high energy density.However,uneven Li deposition behavior still occurs at the top of 3D frameworks owing to the local accumulation of Li ions.To promote uniform Li deposition without top dendrite growth,herein,a layered multifunctional framework based on oxidation-treated polyacrylonitrile(OPAN) and metal-organic framework(MOF) derivatives was proposed for rationally regulating the distribution of Li ions flux,nucleation sites,and electrical conductivity.Profiting from these merits,the OPAN/carbon nano fiber-MOF(CMOF) composite framework demonstrated a reversible Li plating/stripping behavior for 500 cycles with a stable Coulombic efficiency of around 99.0% at the current density of 2 mA/cm~2.Besides,such a Li composite anode exhibited a superior cycle lifespan of over 1300 h under a low polarized voltage of 18 mV in symmetrical cells.When the Li composite anode was paired with LiFePO_(4)(LFP) cathode,the obtained full cell exhibited a stable cycling over 500 cycles.Moreover,the COMSOL Multiphysics simulation was conducted to reveal the effects on homogeneous Li ions distribution derived from the above-mentioned OPAN/CMOF framework and electrical insulation/conduction design.These electrochemical and simulated results shed light on the difficulties of designing stable and safe Li metal anode via optimizing the 3D frameworks.

Effect of Heat-Insulating Layer Thickness on Melting Rate of Ice Fixed Abrasives Polishing Pad

The formula of the thickness of the heat-insulating layer is deduced via heat transfer analysis,according to the principle of heat transfer in limited space.Polishing experiments are carried out using the same technological parameters.Compared with the polishing experimental results,the heat transfer model is proved to be correct.As validated by the experimental results,polyurethane heat-insulating layer can effectively improve the service life of the ice fixed abrasive pad and alleviate the melting rate in the polishing process to improve the polishing quality proposed.The heat transfer model provides theoretical basis for research of temperature field of ice fixed abrasive polishing.

Experimental study on the penetration characteristics of leaking molten salt in the thermal insulation layer of aluminum silicate fiber

The molten salt leakage accident is an important issue in the nuclear safety analysis of molten salt reactors.While the molten salt leaks from the pipeline or storage tank,it will contact the insulation layer outside;hence,the processes of penetration and spreading play an important role in the development of leakage accidents.In this study,the penetration and diffusion of leaking molten salt(LMS)in an aluminum silicate fiber(ASF)thermal insulation layer were studied experimentally.A molten salt tank with an adjustable outlet was designed to simulate the leakage of molten salt,and the subsequent behavior in the thermal insulation layer was evaluated by measuring the penetra-tion time and penetration mass of the LMS.The results show that when the molten salt discharges from the outlet and reaches the thermal insulation layer,the LMS will penetrate and seep out from the ASF,and a higher flow rate of LMS requires less penetration time and leaked mass of LMS.As the temperature of the LMS and thickness of the ASF increased,the penetration time became longer and the leaked mass became greater at a lower LMS flow rate;when the LMS flow rate increased,the penetration time and leaked mass decreased rapidly and tended to flatten.

OPTICAL EFFECTS AND MICROSTRUCTURE OF BURIED INSULATOR LAYER FORMED BY O^+ AND N^+ CO-IMPLANTATION

The microstructure and optical properties of a buried layer formed by O+(200keV,1.8×1018/cm2)and N+(180 keV,4×1017/cm2)co-implantation and annealed at 1200℃for 2 h have been investigated by Auger electron,IR absorption and reflection spectroscopicmeasurements.The results show that the buried layer consists of silicon dioxide and SiOx（x【 2）and the nitrogen segregates to the wings of the buried layer where it forms an oxynitride.Bydetail theoretical analysis and computer simulation of the IR reflection interference spectrum,therefractive index profiles of the buried layer were obtained.

Study on influences of TiN capping layer on time-dependent dielectric breakdown characteristic of ultra-thin EOT high-k metal gate NMOSFET with kMC TDDB simulations

The thickness effect of the TiN capping layer on the time dependent dielectric breakdown（TDDB） characteristic of ultra-thin EOT high-k metal gate NMOSFET is investigated in this paper.Based on experimental results,it is found that the device with a thicker TiN layer has a more promising reliability characteristic than that with a thinner TiN layer.From the charge pumping measurement and secondary ion mass spectroscopy（SIMS） analysis,it is indicated that the sample with the thicker TiN layer introduces more Cl passivation at the IL/Si interface and exhibits a lower interface trap density.In addition,the influences of interface and bulk trap density ratio Nit/Not are studied by TDDB simulations through combining percolation theory and the kinetic Monte Carlo（kMC） method.The lifetime reduction and Weibull slope lowering are explained by interface trap effects for TiN capping layers with different thicknesses.

Transforming a Two-Dimensional Layered Insulator into a Semiconductor or a Highly Conductive Metal through Transition Metal Ion Intercalation

Atomically thin two-dimensional(2D) materials are the building bricks for next-generation electronics and optoelectronics, which demand plentiful functional properties in mechanics, transport, magnetism and photoresponse.For electronic devices, not only metals and high-performance semiconductors but also insulators and dielectric materials are highly desirable. Layered structures composed of 2D materials of different properties can be delicately designed as various useful heterojunction or homojunction devices, in which the designs on the same material(namely homojunction) are of special interest because preparation techniques can be greatly simplified and atomically seamless interfaces can be achieved. We demonstrate that the insulating pristine ZnPS_3, a ternary transition-metal phosphorus trichalcogenide, can be transformed into a highly conductive metal and an n-type semiconductor by intercalating Co and Cu atoms, respectively. The field-effect-transistor(FET) devices are prepared via an ultraviolet exposure lithography technique. The Co-ZnPS_3 device exhibits an electrical conductivity of 8 × 10^(4) S/m, which is comparable to the conductivity of graphene. The Cu-ZnPS_3 FET reveals a current ON/OFF ratio of 1-05 and a mobility of 3 × 10^(-2 )cm^(2)·V^(-1)·s^(-1). The realization of an insulator, a typical semiconductor and a metallic state in the same 2D material provides an opportunity to fabricate n-metal homojunctions and other in-plane electronic functional devices.

Modification of the Hybridization Gap by Twisted Stacking of Quintuple Layers in a Three-Dimensional Topological Insulator Thin Film

Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is below some critical thickness, will hybridize and open a gap in the surface state structure. The hybridization gap can be tuned by various parameters such as film thickness and inversion symmetry, according to the literature. The three-dimensional strong topological insulator Bi(Sb)Se(Te) family has layered structures composed of quintuple layers(QLs) stacked together by van der Waals interaction. Here we successfully grow twistedly stacked Sb_2Te_3 QLs and investigate the effect of twist angels on the hybridization gaps below the thickness limit. It is found that the hybridization gap can be tuned for films of three QLs, which may lead to quantum spin Hall states.Signatures of gap-closing are found in 3-QL films. The successful in situ application of this approach opens a new route to search for exotic physics in topological insulators.

Thermal Insulation Distribution Pattern of Layered Clothing Ensemble

With a thermal manikin, the distribution pattern of thermal insulation in multi-layered clothing ensemble is studied. It is found that the thermal insulation of multi-layered clothing ensemble has certain statistical relationship with the thermal insulation of each layer, and the prediction equation has been established.

稠油井内衬保温油管热损失分析及开采参数优化

针对塔河油田稠油开采过程中原油热量损失大、资源浪费的问题,开展内衬保温油管开采技术研究。基于井筒稳态热传递与地层非稳态热传递理论,建立了稠油井井筒热传递数学模型,评价了不同内衬材料油管的保温性能,揭示了含水率、日产液量及内衬保温油管下深对井筒温度的影响规律。研究表明:内衬聚酮防腐层与气凝胶保温层的保温油管保温性能最佳,日产液量和保温油管下深对井口温度影响较大,含水率对井口温度的影响较小;日产液量大于72 t/d且保温油管下深大于3 500 m时,可满足稠油开采的温度要求。该研究明确了内衬保温油管保温的可行性,可为油田保温油管内衬的选材、稠油开采工艺参数的制订提供技术依据。

寒区隧道防冻保温层隔热作用机理及其厚度影响因素研究

针对寒冷地区公路隧道防冻保温层表面铺设,共设置了21组计算工况,通过对年周期下隧道防冻保温层、衬砌结构和围岩沿径向温度场变化以及各工况所需的防冻保温层厚度进行数值模拟计算,研究隧道防冻保温层隔热作用机理及其所需厚度的影响因素。结果表明:防冻保温层隔热作用显著,主要体现在使隧道衬砌结构和围岩年温度振幅降低上,同时年平均温度也有一定升高;随着防冻保温层铺设厚度增大,隧道衬砌结构和围岩年平均温度和年温度振幅分别呈指数函数升高和降低,相应的年最低温度也呈指数函数升高,防冻保温层厚度越大,隔热效果越好,但是隔热效率不断降低;围岩导热系数越大,导温系数越小,防冻保温层隔热效果越显著;防冻保温层所需厚度随围岩导热系数和围岩初始温度升高呈指数函数减小,随围岩导温系数升高呈对数函数增加,随年平均气温和年温度振幅升高分别呈线性减小和增加,防冻保温层厚度应综合考虑以上各因素进行计算确定。

内埋可变导热管建筑顶面隔热层节能分析

为减少室内空调能耗,文中对目前广泛使用的在建筑顶面之上铺制隔热层的建筑节能方法做进一步优化。文中以北京地区某建筑为例进行计算分析发现,隔热层的高热阻在夜间不利于建筑顶层白天积累的热量向外界排散。为在夏季夜间减小隔热层热阻,加速建筑顶层白天积累热量的排散,提出一种内埋可变导热管的建筑顶面隔热层,即在建筑顶面隔热层内间隔一定距离埋制可变导热管。夏季白天工况,可变导热管不启动,为高热阻状态;夏季夜间工况,可变导热管传热能力强,减小了隔热层热阻,加快了夜间建筑顶层结构热量的向外排散,计算结果表明,按照间隔0.3m铺制可变导热管的隔热层比铺制普通隔热层的空调制冷量下降15.1%;冬季工况热管传热能力非常差,隔热层保持了高热阻状态,避免了室内热量损耗。这种方法节能效果明显,可为建筑节能研究工作提供参考。

影像变形的中空玻璃厚度测量与分析

选取某玻璃幕墙项目同一区域内已有影像变形的不同分格尺寸的中空玻璃,测量了中空玻璃空气层厚度和中空玻璃外片平面外凹陷,并对中空玻璃外片凹陷变形进行等效荷载作用校核分析,为影像变形的中空玻璃整改和安全使用提供了数据支持。

纳米纤维素基材料在柔性电子器件中的应用

目的由于纳米纤维素基材料良好的柔韧性、热力学性能和高透明度,近年来在柔性电子产品中引起越来越多的关注。通过综述该领域的研究进展,将有助于研究人员更高效地开展研究。方法综述3类纳米纤维素的制备方法及将纳米纤维素基材料应用在柔性电子产品中的研究进展。分别阐述纳米纤维素基材料应用于器件柔性衬底及绝缘材料的研究实例,并讨论纳米纤维素在各种应用方向中的优势以及存在的问题,最后对材料的未来应用前景进行展望。结论纳米纤维素是天然纤维素与纳米技术结合的产物,可主要划分为纤维素纳米纤丝、纤维素纳米晶以及细菌纤维素3类。近年来,纳米纤维素基材料作为电子器件柔性衬底、绝缘材料等研究均有许多成果问世。虽然纳米纤维素基电子器件的开发还主要停留在实验室阶段,但是与传统的石油化工产品相比,纳米纤维素具有原材料丰富、环保可降解等优点。对纳米纤维素基新型材料的开发利用,有助于解决人类社会中日益严重的电子垃圾问题。

可陶瓷化EPDM绝热材料的烧蚀特性及陶瓷化机理

绝热层中炭化层的特性与其耐烧蚀性能紧密相关。通过对可陶瓷化三元乙丙(EPDM)绝热材料氧乙炔烧蚀特性和成分进行表征分析,得到了线烧蚀率与炭化层不同参数之间的相关性,分析了类陶瓷炭化层的形成机理。结果表明,当可陶瓷化硅树脂填料含量在35~40 phr时,炭化层结构更致密,硬度更高,孔隙率更小,陶瓷产物更多,有效提高了EPDM绝热层的耐烧蚀性能;线烧蚀率与炭化层的结构与成分之间存在强相关性;类陶瓷炭化层结构的形成主要分为高分子聚合物的热分解、小分子物质的化学气相沉积、烧蚀表面SiC的原位生成和熔融SiO_(2)在炭化层中的填充粘结四个阶段,最终形成一种Si—O—C的复相陶瓷结构。

四方相纳米钛酸钡粉体的制备及性能研究

在传统固相法制备四方相纳米钛酸钡粉体中,碳酸钡前驱体的分散性与粒径对所得钛酸钡的形貌、粒径以及介电性能起重要作用。本研究以氢氧化钡与干冰为原料,通过控制氢氧化钡的浓度,制备了碳酸钡粉体,然后以此为原料,制备了钛酸钡粉体和陶瓷,并研究了钛酸钡陶瓷的介电性能。结果表明:本研究制得粒径为180 nm的短棒状碳酸钡粉体,和粒径为400 nm的高分散、高均匀、纯四方相的钛酸钡粉体。在1250℃下煅烧制得钛酸钡陶瓷,其介电常数为4885,介质损耗因数为0.0189。

液氦储罐高真空多层绝热结构影响研究

为了明确液氦储罐真空多层绝热结构的最佳层密度,采用Lockheed模型研究热流密度与层密度的关系,确定最佳层密度,探讨绝热层厚度、环境温度、绝热空间真空度对液氦储罐绝热性能的影响。研究结果表明:液氦储罐最佳层密度为41层/cm;绝热层真空度减小,热流密度下降,真空度下降到一定值后,热流密度几乎不再下降;热流密度与环境温度、绝热层厚度分别呈正、负相关,当厚度增加到一定值后,热流密度下降速率减小。在实际确定绝热层厚度和真空度时,应兼顾经济性和绝热性能。研究结果可为液氦储罐高真空多层绝热结构的设计提供参考。

功能梯度复合材料的制备及隔热性能模拟研究

基于航空航天热防护技术对多功能隔热材料的需求,制备了由力学缓冲层、高温隔热层和核心隔热层构成的功能梯度复合材料,材料应力适应性强、耐温性高、隔热性能优异。通过模拟计算的方法对复合材料的隔热性能进行研究,结果表明,30mm厚的复合材料在1000℃、1000s的热载荷下隔热性能优异,各功能层厚度影响复合材料的传热背温。随着力学缓冲层/高温隔热层相对厚度的增大,复合材料背温和核心隔热层热面温度均增大,由于核心隔热层耐温极限的限制,力学缓冲层厚度最大为12mm,此时复合材料背温为26.10℃。力学缓冲层/核心隔热层、高温隔热层/核心隔热层相对厚度增大时,复合材料背温增大,核心隔热层热面温度减小,力学缓冲层的厚度最小为6mm,此时复合材料背温为20.21℃,高温隔热层的厚度最小为10mm,此时复合材料背温为22.58℃。

绝热层对界面粘接性能影响研究

本文研究了丁腈橡胶(NBR)和三元乙丙橡胶(EPDM)两类绝热层的种类,以及绝热层的厚度、烘干条件等条件因素对端羟基聚丁二烯(HTPB)/异佛尔酮二异氰酸酯(IPDI)推进剂的界面粘接性能的影响。研究结果表明,NBR绝热层和EPDM绝热层对HTPB/IPDI推进剂的界面粘接性能均有明显的弱化作用。相比于EPDM绝热层,NBR绝热层对粘接性能的影响更大。随着NBR绝热层厚度的增加,对推进剂界面粘接性能的弱化作用加剧。通过对NBR绝热层的烘干预处理可以减弱绝热层对推进剂界面粘接性能的不利影响。

超稠油老区氮气辅助VHSD开发数值模拟

转直井辅助水平井重力泄油(VHSD)开发方式已成为超稠油老区进一步提高区块采油速度、油藏采收率的重要调整手段。氮气辅助VHSD的增能提压、顶部隔热效应可有效解决超稠油老区吞吐后压力保持程度低、驱泄操作压力低、蒸汽腔温度低的问题,进而实现节约蒸汽用量、提高产油水平、提升油汽比和减耗降碳的目的。以克拉玛依油田九区某VHSD开发单元为例,采用数值模拟方法分析了在氮气辅助VHSD开发过程中注氮时机、注氮方式、注氮量等参数对提压增能、建立隔热层的影响,以及采出速度和累计注采的变化特点。研究表明,转驱泄初期采用段塞方式注入氮气可有效建立隔热层;矿场试验表明,井组油汽比提升0.025,日产油提升0.7 t,取得了较好的应用效果。研究成果为同类型超稠油老区氮气辅助VHSD效益开发提供了技术借鉴。