Numerical Simulation and Experimental Verification of Temperature Distribution of Piezoelectric Stack with Heating and Thermal Insulation Device

This paper discusses the temperature field distribution of piezoelectric stack with heating and thermal insulation device in cryogenic temperature environment. Firstly,the model of the piezoelectric damper is simplified and established by using partial-differential heat conduction equation. Secondly,the two-dimensional Du Fort-Frankel finite difference scheme is used to discretize the thermal conduction equation,and the numerical solution of the transient temperature field of piezoelectric stack driven by heating film at different positions is obtained by programming iteration. Then,the cryogenic temperature cabinet is used to simulate the low temperature environment to verify the numerical analysis results of the temperature field. Finally,the finite difference results are compared with the finite results and the experimental data in steady state and transient state,respectively. Comparison shows that the results of the finite difference method are basically consistent with the finite element and the experimental results,but the calculation time is shorter. The temperature field distribution results obtained by the finite difference method can verify the thermal insulation performance of the heating system and provide data basis for the temperature control of piezoelectric stack.

Analyses of non-aqueous reactive polymer insulation layer in high geothermal tunnel

The scenario of geothermal tunnel is commonly observed around the world,and increases with the new constructions in the long and deep tunnels,for example in China.Tunnel insulation is generally divided into active and passive insulation.In passive insulation,it is an effective way to set low thermal con-ductivity materials as the thermal insulation layer as the choice of insulation material mainly depends on the thermal conductivity.Polymer is a kind of material with good geothermal performance,but there are relatively few studies.In this context,the transient plane source(TPS)method was used to measure the thermal conductivity of the developed polymer.Then,the temperature field of the high geothermal tunnel insulated by the non-aqueous reactive polymer layer was simulated.With the parametric analysis results,the suggestions for the tunnel layers were proposed accordingly.It revealed that the thermal conductivity of polymer first increases and then decreases with temperature.There are two rising sec-tions(?40e10?C and 20e90?C),one flat section(10e20?C)and one descending section(>90?C).It is observed the thermal conductivity of polymer increases with increase of the density of insulation layer and the density,and the thermal conductivity decreases when exposed to high temperatures.The temperature of the surrounding rocks increases with increase of the thermal conductivity and the thickness of polymer.Finally,a more economical thickness(5 cm)was proposed.Based on the parametric study,a thermal insulation layer with thermal conductivity less than 0.045 W/(m K),thickness of 5 cm and a density less than 0.12 g/cm 3 is suggested for practice.

Analytical and numerical modeling for the effects of thermal insulation in underground tunnels

The heat How generated from the infinite rock mass surrounding the underground tunnels is a major cause for the increasing cooling demands in deep mine tunnels.Insulation layers with lower thermal conductivities on tunnel walls and roof ceilings are believed to supply a thermo-barrier for heat abatement.However,it is found that no systematic theoretical investigations were made to predict and confirm the effectiveness of underground thermal insulation.Specifically,investigations on the underground insulation problems involving heat flows through the semi-infinite hot rock mass and insulation layer were not sufficient.Thus,in this paper,the thermal characteristics,accompanied with heat flow through the semi-infinite rock mass and the insulation layer,were modeled by both analytical and numerical methods with focus on underground mine tunnels.The close agreements between models have indicated that the thermal insulation applied on tunnel surfaces is able to provide promising heat abatement effects.

Preparation and Recipe Optimization of Water-based Architectural Heat Insulation Coatings

Water-based architectural heat insulation coatings were studied to overcome the drawbacks of conventional inorganic silicate heat insulation coatings. The heat insulation coatings were prepared with the method of mechanical agitation when the mixed organic polymer emulsions were used as binder of the coatings and the mixed heat insulating aggregates were applied as powder, and some assistants were also added. Water temperature difference in the plastic container, which was coated with heat insulation coatings, represented the heat-insulating property of the coatings. The influences of components of mixed polymer emulsion, mass ratio of polymer emulsion to powder, particle size of heat insulating aggregates, added amount of air entraining admixture and the match of thickeners on the properties of the coatings were studied. The experimental results show that the heat insulation coatings with good finishing, heat-insulation property and artificial weathering can be prepared when the binder is composed of 66.92% styrene-acrylic emulsion, 16.59% elastic emulsion and 16.49% silicone-acrylic emulsion, the mass ratio of polymer emulsion to powder is 0.45, the particle size of heat insulating aggregates is in the rang of 200 and 250 mesh size, the added amount of sericite is 15%, and the added amount of air entraining admixture is in the range of 1.0% and 1.5% and the thickeners are the mixtures of ASE-60 and RM-5000.

CFD Simulations of Wind Effect on Net Solar Heat Gain of South Walls with Internal Insulation

Computational fluid dynamics( CFD) techniques are used to investigate effects of both wind direction and wind speed on net solar heat gain of south wall with internal insulation in winter.Results show that wind effect has a significant influence on the net solar heat gain,where the impact of wind direction is stronger than that of wind speed. For regions in lower reaches of the Yangtze River,difference of their average net solar heat gains( NSHGS) is about 20% due to various wind speeds and wind directions.Buildings in districts with a dominant wind direction of north achieve the highest solar energy utilization.

Recent Progress of Bionic Hierarchical Structure in the Field of Thermal Insulation Protection

Some living organisms with hierarchical structures in nature have received extensive attention in various fields.The hierarchical structure with multiple pores,a large number of solid-gas interfaces and tortuous conduction paths provide a new direction for the development of thermal insulation materials,making the living creatures under these extreme conditions become the bionic objects of scientific researchers.In this review,the research progress of bionic hierarchical structure in the field of heat insulation is highlighted.Polar bears,cocoons,penguin feathers and wool are typical examples of heat preservation hierarchy in nature to introduce their morphological characteristics.At the same time,the thermal insulation mechanism,fractal model and several preparation methods of bionic hierarchical structures are emphatically discussed.The application of hierarchical structures in various fields,especially in thermal insulation and infrared thermal stealth,is summarised.Finally,the hierarchical structure is prospected.

Ni Flower/MXene-Melamine Foam Derived 3D Magnetic/Conductive Networks for Ultra-Efficient Microwave Absorption and Infrared Stealth

The development of multifunctional and efficient electromagnetic wave absorbing materials is a challenging research hotspot.Here,the magnetized Ni flower/MXene hybrids are successfully assembled on the surface of melamine foam(MF)through electrostatic self-assembly and dip-coating adsorption process,realizing the integration of microwave absorption,infrared stealth,and flame retardant.Remarkably,the Ni/MXene-MF achieves a minimum reflection loss(RLmin)of−62.7 dB with a corresponding effective absorption bandwidth(EAB)of 6.24 GHz at 2 mm and an EAB of 6.88 GHz at 1.8 mm.Strong electromagnetic wave absorption is attributed to the three-dimensional magnetic/conductive networks,which provided excellent impedance matching,dielectric loss,magnetic loss,interface polarization,and multiple attenuations.In addition,the Ni/MXene-MF endows low density,excellent heat insulation,infrared stealth,and flame-retardant functions.This work provided a new development strategy for the design of multifunctional and efficient electromagnetic wave absorbing materials.

Analyses on performances of heat and multilayer reflection insulators

This research was conducted to study the performances of the heat and multilayer reflection insulators used for buildings in South Korea to realize eco-friendly, low-energy-consumption, green construction, and to contribute to energy consumption reduction in buildings and to the nation＇s greenhouse gas emission reduction policy （targeting 30% reduction compared to BAUCousiness as usual） by 2020）. The heat insulation performance test is about the temperatures on surfaces of test piece. The high air temperature and the low air temperature were measured to determine the overall heat transfer coefficient and thermal conductivity. The conclusions are drawn that the heat transmission coefficients for each type of existing reflection insulator are： A-1 （0.045 W/（m-K））, A-2 （0.031 W/（m.K））, A-3 （0.042 W/（m.K））, A-4 （0.078 W/（m.K））, and the average heat conductivity is 0.049 W/（m-K）; The heat conductivity for each type of Styrofoam insulator are 0.030 W/（m.K） for B-l, 0.032 W/（m-K） for B-2, 0.037 W/（m＇K） for B-3, 0.037 W/（m.K） for B-4, and the average heat conductivity is 0.035 W/（m＇K） regardless of the thickness of the insulator; The heat conductivity values of the multilayer reflection insulators are converted based on the thickness and type C-1 （0.020 W/（m.K））, C-2 （0.018 W/（m.K））, C-3 （0.016 W/（m.K））, and C-4 （0.012 W/（m.K））; The multilayer reflection insulator keeps the indoor-side surface temperature high （during winter） or low （in summer）, enhances the comfort of the building occupants, and conducts heating and moisture resistance to prevent dew condensation on the glass-outer-wall surface.

Hydrothermal Solidification of Diatomite and Its Heat Insulating Property

To meet the commercial requirements of inorganic heat insulators,the mixture of diatomite and Ca(OH)2 are evenly dispersed,mold-compacted,and then hydrothermally solidified due to the formation of tobermorite under an autoclaved process.Systematic investigations of the preparation conditions(including mix ratio,autoclaved factors,mold pressure,etc)were carried out to optimize the serving properties of such tobermorite-based products.As a result,a compressive strength of more than 30 MPa was realized for the specimen in high density(about 1.30(g·cm-3)).On the contrary,the specimen in light weight for example 0.63(g·cm-3)typically showed a thermal conductivity of around 0.12(W·m-1·K-1).The present work developed a feasible way to produce and to control the serving properties of diatomite-based heat insulators by a process of hydrothermal solidification,in which the optimized value of Ca/Si ratio was proposed to be 0.6~0.7,while the water content is 25% in weight,and hydrothermal reaction is performed at 180 ℃ for no more than 24 hours.

PRINCIPLE AND METHOD OF CVD MODIFIED TECHNIQUE OF FOAM ASBESTOS

In this paper the method of chemical vapor depostion is used to discuss the principle and method of foam asbestos, a new heat insulation material whose synthetical properties are improved remarkably after modifying. It becomes one of the best heat insulation materials and, a kind of safety, no social effects of pullution material to a great extent.

Properties of plasma sprayed NiCrAlY+（ZrO2+Y2O3） coating on refractory steel surface

NiCrAlY+(ZrO_2+Y_2O_3)thermal barrier coating was prepared on the surface of refractory steel 1Cr18Ni9Ti with plasma spraying technique. The phases and microstructure of the thermal barrier coating were determined by scanning electron microscopy(SEM) and X-ray diffraction(XRD). The results show that the bonding between thermal barrier coating and substrate is sound. The surface hardness of 1Cr18Ni9Ti reaches up to 1000 HV, but that of substrate is only 300HV. The patterns sprayed with CoNiCrAlY+(ZrO_2+Y_2O_3) ceramic coating have a good heat insulation effect at 800℃ for heat insulation temperature difference reaches 54℃, which increases the operating temperature and service life of refractory steel.

Review on safe blasting technology in high-temperature coal seams in China

In order to define the development direction of safe blasting technology in high-temperature coal seams in China, this paper presents a systematic, state-of-the-art review on safe blasting technology. Information such as high-temperature coal fire extinguishment and cooling, anti-high-temperature blasting supplies, heat insulation blasting setting, operation procedures for high-temperature blasting, and so on, are presented. Analysis shows that the development of effective technology for coal seam fire extinguishing and cooling, the manufacture of anti-high-temperature blasting supplies, especially priming materials, the development of heat insulation blasting setting, and the establishment of technical specifications suit large-scale blasting design and construction work at high-temperature coal seams, are the essential methods for safe blasting at high temperature coal seams.

Multi-functional and multi-scenario applications for MXene aerogels with synergistically enhanced asymmetric modules

The development of multifunctional materials and synergistic applications of various functions are important conditions for integrated and miniaturized equipment.Here,we developed asymmetric MXene/aramid nanofibers/polyimides(AMAP)aerogels with different modules using an integrated molding process.Cleverly asymmetric modules(layered MXene/aramid nanofibers section and porous MXene/aramid nanofibers/polyimides section)interactions are beneficial for enhanced performances,resulting in low reflection electromagnetic interference(EMI)shielding(specific shielding effectiveness of 2483(dB·cm^(3))/g and a low R-value of 0.0138),high-efficiency infrared radiation(IR)stealth(ultra-low thermal conductivity of 0.045 W/(m·K)and IR emissivity of 0.32 at 3–5μm and 0.28 at 8–14μm),and excellent thermal management performances of insulated Joule heating.Furthermore,these multifunctional AMAP aerogels are suitable for various application scenarios such as personal and building protection against electromagnetic pollution and cold,as well as military equipment protection against infrared detection and EMI.

Synchronous deprotonation–protonation for mechanically robust chitin/aramid nanofibers conductive aerogel with excellent pressure sensing, thermal management, and electromagnetic interference shielding

Aerogels with regularly porous structure and uniformly distributed conductive networks have received extensive attention in wearable electronic sensors,electromagnetic shielding,and so on.However,the poor mechanical properties of the emerging nanofibers-based aerogels are limited in practical applications.In this work,we developed a synchronous deprotonation–protonation method in the KOH/dimethyl sulfoxide(DMSO)system at room temperature for achieving chitin cross-linked aramid nanofibers(CANFs)rather than chitin nanofibers(ChNFs)and aramid nanofibers(ANFs)separately by using chitin and aramid pulp as raw materials.After freeze-drying process,the cross-linked chitin/aramid nanofibers(CA)aerogel exhibited the synergetic properties of ChNF and ANF by the dual-nanofiber compensation strategy.The mechanical stress of CA aerogel was 170 kPa at 80%compressive strain,increased by 750%compared with pure ChNF aerogel.Similarly,the compressibility of CA aerogel was somewhat improved compared to ANF aerogel.The enhancement verified that the crosslinking reaction between ANF and ChNF during the synchronous deprotonation process was formed.Afterwards,the conductive aerogels with uniform porous structure(CA-M)were successfully obtained by vacuum impregnating CA aerogels in Ti_(3)C_(2)T_(x) MXene solution,displaying low thermal conductivity(0.01 W/(m·K)),high electromagnetic interference(EMI)shielding effectiveness(SE)(75 dB),flame retardant,and heat insulation.Meanwhile,the as-obtained CA-M aerogels were also applied as a pressure sensor with excellent compression cycle stability and superior human motion monitoring capabilities.As a result,the dual-nanofiber based conductive aerogels have great potentials in flexible/wearable electronics,EMI shielding,flame retardant,and heat insulation.

Engineering pulp foam with highly improved water stability and multifunctional properties by incorporation of natural rubber and montmorillonite

Considering the aim of carbon neutrality and reducing plastic pollution,lightweight porous materials with good thermal insulation and mechanical robustness derived from renewable resources are in high demand.Cellulose-based pulp foams(PFs)offer considerable potential applications in many fields;however,the cost-effective manufacturing of PFs with satisfactory properties remains challenging.Herein,we demonstrate a simple and low-cost strategy to prepare a novel pulp/natural rubber(PNR)foam by combining wood pulp fiber and natural rubber latex through wet foaming and oven drying,eliminating traditional freeze-drying and solvent exchange processes.The obtained PNR foam exhibited high porosity(98.4%-99.1%),low density(14.1–24.0 mg/cm^(3)),and excellent water stability(without disintegration under magnetic stirring for 14 days).Moreover,montmorillonite(MMT)was easily incorporated into the PNR during the preparation process,improving the mechanical strength and heat insulation of the obtained PNRMMT foam.The optimized PNR-MMT foam could be compressed more than ten times without losing its resilience,exhibiting a compressive strength of 2.7 MPa at 80%strain,five times higher than that of pristine PF.Moreover,the PNR-MMT foam exhibited excellent flame retardant,good“spill”oil absorption,and good antibacterial properties towards Escherichia coli and Bacillus subtilis.Overall,this study provides a facile,sustainable,and low-cost route for manufacturing PNR-MMT foams with high resilience,good thermal insulation,excellent flame retardancy,and strong antibacterial properties,thus highlighting their usage potential in a broad range of applications.

Experiments and numerical study on heat transfer of moist silica aerogel composites at high temperatures

Silica aerogel composites have promising applications in high-temperature heat storage insulation.However,the impact of high temperatures and moisture on their insulation performance remains unclear.To reveal the influences of high temperature and moisture absorption property on the heat transfer of silica aerogel composites,an experimental and numerical study was conducted to explore the micromorphology,thermophysical parameters,moisture absorption characteristics,and temperature response.The service temperature limit of the silica aerogel composite has been clarified.Measurements have conducted for the thermal conductivity,specific heat capacity,thermal diffusivity,specific surface area,density,porosity,and pore size distribution of the heated silica aerogel composite(at temperatures of 600,800,1,000,1,100 and 1,200℃).The moisture absorption characteristic curve at 20℃ has been obtained.Thermal testing of silica aerogel composites under varying heating temperatures and moisture content has been completed.Additionally,a numerical method has been developed to calculate the temperature curve of moist silica aerogel composites.The insulation performance of silica aerogel composite with varying moisture contents depends on the game between thermal conductivity and latent heat.Compared with the negative effect of the moisture content on insulation performance,the positive influence of moisture evaporation and heat absorption is dominant in situations involving temperatures higher than the phase transition temperature.

Multifunctional aramid nanofibers reinforced RGO aerogels integrated with high-efciency microwave absorption, sound absorption and heat insulation performance

Although lightweight and three-dimensional(3 D) graphene aerogels are highly desirable for microwave absorption(MA) due to their high porosity,specific surface area,and 3 D conductive network,it still remains a large challenge to construct a multifunctional application framework to quickly adapt to the complex practical environment,making it to be efficiently applied in a variety of complex situation.Herein,multifunctional aramid nanofibers(ANFs) reinforced reduced graphene oxide aerogels(RGO@ANF) have been achieved by in-situ gel reaction,freeze-drying,and thermal annealing processes.The introduced ANFs in RGO aerogels can prevent the graphene sheets from over-stacking and enhance the connectivity of cell walls,thus leading to excellent compression resistance,MA,sound absorption,and thermal insulation performance.Under 70% strain,the maximum compressive stress of RGO@ANF aerogel reaches78.8 kPa,and reversible compressibility with reliable resistance to fatigue for 100 compressive cycles at20% strain.Further,the RGO@ANF aerogel exhibit a minimum reflection loss(RL_(min)) of-56.5 dB and a maximum effective absorption bandwidth(EAB) of 7.0 GHz at a thickness of 2.8 mm,basically covering the X and Ku bands.Moreover,the hybrid aerogel exhibited excellent sound absorption with an average absorption coefficient> 0.56 at 2-6 kHz and good thermal insulation performance with low thermal conductivity of about 49.18 mW m-1K-1.The integrated graphene aerogels with such multifunctional performances hold a great promise for applications such as MA,sound absorption,and heat insulation.

Rigid foam polyurethane （PU） derived from castor oil （Ricinus communis） for thermal insulation in roof systems

This paper discusses the response of the thermal insulation Lining of rigid foam potyurethane （PU） derived from castor oil （Ricinus communis） in heat conditions, based on dynamic climate approach. Liners have been widely used, because the coverage of buildings is responsible for the greatest absorption of heat by radiation, but the use of PU foam deMved from this vegetal oil is unprecedented and has the advantage of being biodegradable and renewable. The hot wire paraLleL method provided the thermal conductivity vatue of the foam. The thermo- gravimetric analysis enabled the study of the foam decomposition and its Lifetime by kinetic evaLuation that involves the decomposition process. The PU foam thermal behavior analysis was performed by coLlecting experimental data of internal surface temperature measured by thermocouples and assessed by representative episode of the climatic fact. The results Lead to the conclusion that the PU foamderived from castor oit can be applied to thermat insulation of roof systems and is an environmentaLLy friendly materiaL.

Preparation,with graphene,of novel biomimetic selfhealing microcapsules with high thermal stability and conductivity

This paper reports a comparative study of microcapsules with enhanced thermal stability and electrical conductivity inspired by the bionic thermal insulation of birds’feathers for self-healing aged asphalt.The work is based on an in situ polymerization with composite shell components of graphene and hexamethoxymethylmelamine resin.By using graphene,microcapsules with rough surfaces are achieved,improving the interface between microcapsules and asphalt.In addition,the microcapsules’initial thermal decomposition temperature is appropriately high,so that the stability of the microcapsule in the asphalt highway system is protected.The proportion of graphene in the microcapsule shell can regulate the microcapsule’s heat resistance because graphene modifies the shell’s structural makeup.Additionally,the microcapsules’electrical conductivity is relatively high.The self-healing capability of bitumen sharply increases,providing benefit to the effect of microcapsules on the properties of aged asphalt.

Multifunctional protective aerogel with superelasticity over−196 to 500℃

Protective materials that possess superelasticity and multifunctionality over a broad temperature range are urgently needed in various advanced applications.However,under harsh work conditions,the performance of current materials may largely deteriorate to lose protective functionality.Herein,we report a bidirectionally oriented multi-walled carbon nanotubes(MWCNTs)-reinforced chitosan carbon aerogel(CS-MWCNT)that possesses superelasticity,high electromagnetic interference shielding,thermal insulation,and infrared stealth at both low temperatures(such as liquid nitrogen)and high temperatures(such as alcohol flames).Highly oriented lamellar arch structures combined with an MWCNTs-reinforced carbon skeleton act as elastic segments to disperse the stress during compression and endow CS-MWCNT with the ability to recover to almost the original size after being compressed at−196-500℃.The lamellar structures make CS-MWCNT thermally insulating and infrared stealth with a low thermal conductivity of~0.03 W/(m·K).Furthermore,a high electromagnetic interference(EMI)shielding effect of 64 dB is realized via an absorption-dominant EMI shielding mechanism derived from the successive inherently conductive carbon lamella,and the EMI shielding performance is largely maintained after treatment under extreme conditions like low temperature,high temperature,as well as cyclic compression.This work provides a new strategy for the development of temperature-invariant multifunctional aerogels for harsh environment applications.