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.

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.

Quantitative Analysis of Azodicarbonamide in Insulation Layers of Extruded Cables by HPLC–UV Detection

Azodicarbonamide(ADC),which has been abundantly used in the creation offoamed plastics as a blowing and foaming agent,has attracted more and more attention in recent years due to the health risks associated with its consumption.ADC is actually on the REACH(Registration,Evaluation,Authorization and Restriction of Chemicals)regulation Candidate List of Substances of Very High Concern,and the residual content in products needs to be confirmed by the end users according to regulations.Therefore,the determination and monitoring of ADC in plastic products is necessary and crucial not only for the growth of ADC global market but also for the health of the public.In this work,a quantitative method for ADC in insulation layers of cables was developed by using optimized total dissolution methodology(TDM)for sample preparation followed by HPLC under HILIC conditions with UV absorbance detection.The linear range of this method was 6–600μg·g^(-1) ,and the limit of detection(LOD)and limit of quantitation(LOQ)were 0.94 and 3.1μg·g^(-1) in solution,respectively.The method has good recovery and precision,and is easy to operate.It meets the needs of the industry and is conducive to the growth of ADC global market.This method is expected to be applicable to ADC quantitation in other polyolefin products.

Numerical simulation of vibrational response characteristics of railway subgrades with insulation boards

This study presents a numerical method based on the surface temperature data and the ground temperature increase in Daqing for predicting temperature field distribution in the Binzhou Railway subgrade and analyzing the temporal and spatial distribution of freeze−thaw status of railway subgrade.The calibrated numerical method is applied to simulate the temperature field distribution and roadbed vibrational response of the railway subgrade with a thermal insulation layer at different seasons.The results show the following:(1)The thermal insulation layer can remarkably increase the soil temperature below it and maximum frost depth in the subgrade.(2)Thermal insulation can effectively reduce the subgrade vibration and protect it from frost damage.(3)Given that the strength requirements are met,the insulation layer should be buried as shallow as possible to effectively reduce the subgrade vibration response.The research findings provide theoretical support for the frost damage prevention of railway subgrades in seasonally frozen regions.

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.

Research on the Novel Honeycomb-Like Cabin Based on Computer Simulation

The antiknock capability and thermal protection performance of rescue capsules mainly depend on the structural design of the cabin.By designing a new type of cabin structure,it can resist the impact of explosion shock waves and thermal shocks.In this paper,a new honeycomb-like cabin is proposed;the model has a novel thermal insulation layer design.Then,the antiknock capabilities and thermal protection analysis are carried out by using computer software.The“Autodyn”analysis module in ANSYS Workbench 17.0 has been used to simulate the explosion of TNT with a certain quality in a single room.The pressure map over time and the pressure variation curve at different locations for a single room are obtained.Through the analysis module“Transient Structural,”the stress and deformation of the honeycomb-like cabin under the blast load are simulated.The“Transient Thermal”analysis module in the finite element software is used to conduct a transient thermal analysis on the cabin structure.The temperature map and the temperature rise curve of each layer of the cabin cases are obtained.The analysis results indicate that the honeycomb-like cabin design has a good antiknock capability and thermal protection performance,and it can meet the usage requirements of the rescue capsule under dangerous conditions.

IGZO/ZTO TFTs with Modulated Double Channel of Thickness Structures

The device characteristics of IGZO/ZTO(indium-gallium-zinc oxide/zinc-tin oxide)TFTs(thin film transistors)with modulated channels were investigated.The field effect mobility was enhanced to 20.4 cm2/Vs in the channel-modulated TFT.The electrical performance of the TFT device was improved by the insertion of a high carrier concentration layer at the channel/gate insulator interfaces.It was due to the enhancement of carrier accumulation and the reduction of parasitic resistance via channel modulation.The threshold voltage was controlled at appropriate value.These results indicate that the device characteristic of TFTs can be enhanced by the modulated channel structure.

Organic thin film transistors with a SiO_2/SiN_x/SiO_2 composite insulator layer

We have investigated a SiO2/SiNx/SiO2composite insulation layer structured gate dielectric for an organic thin film transistor(OTFT) with the purpose of improving the performance of the SiO2gate insulator. The SiO2/SiNx/SiO2composite insulation layer was prepared by magnetron sputtering.Compared with the same thickness of a SiO2insulation layer device,the SiO2/SiNx/SiO2composite insulation layer is an effective method of fabricating OTFT with improved electric characteristics and decreased leakage current.Electrical parameters such as carrier mobility by field effect measurement have been calculated.The performances of different insulating layer devices have been studied,and the results demonstrate that when the insulation layer thickness increases,the off-state current decreases.

Influence of traffic on the temperature field of tunnel in cold region:A case study on the world’s longest highway spiral tunnel

The impact of the piston wind caused by vehicle traffic on the temperature field distribution of the tunnel cannot be ignored,especially in spiral tunnels,where the temperature field distribution is more complicated than that in straight tunnels.Based on the world’s longest highway spiral tunnel,this study explores the influence of traffic on the temperature fields of spiral and straight tunnels,and proposes a new design method for laying length of insulation layer.The results show that traffic has a significant effect on the temperature field dis-tribution in the tunnel.The influence degree of different traffic elements decreases in the following order:average vehicle speed>daily traffic>morning rush hour>evening rush hour.The temperature field distribution of spiral tunnels is asymmetry on the left and right compared with straight tunnels,while the influence degree of traffic on the outside of spiral tunnels is similar to that of straight tunnels.Due to the difference of wind direction and traffic direction at different tunnel openings,an asymmetric insulation layer laying method is proposed.It is suggested that the lengths of the insulation layers of the Jinjiazhuang Tunnel should be 1200 m for the right tunnel inlet,700 m for the right tunnel outlet,700 m for the left tunnel inlet,and 1400 m for the left tunnel outlet.