Thermal radiative properties of metamaterials and other nanostructured materials: A review

The ability to manufacture, control, and manipulate structures at extremely small scales is the hallmark of modern technologies, including microelectronics, MEMS/NEMS, and nano-biotechnology. Along with the advancement of microfabrication technology, more and more investigations have been performed in recent years to understand the influence of microstructures on radiative properties. The key to the enhancement of performance is through the modification of the reflection and transmission properties of electromagnetic waves and thermal emission spectra using one-, two-, or three-dimensional micro/nanostructures. This review focuses on recent developments in metamaterials-manmade materials with exotic optical properties, and other nanostructured materials, such as gratings and photonic crystals, for application in radiative energy transfer and energy conversion systems.     

Single-layer heat mirror films and an improved method for evaluation of its optical and radiative properties in infrared

A technique for preparing single heat mirror films with high quality is described. We also present an improved method for evaluating its optical and thermal radiative properties in the infrared region (2.5<λ<25 μm). The calculated results agree well with that obtained by experimental measurements. The results calculated by using the simple Hagen–Rubens relation are also given. It is shown that the Hagen–Rubens relation is not accurate to predict the thermal radiative properties for the transparent semiconducting oxide films, such as indium tin oxides, prepared in our studies.     

The research applications of new heat insulation composite material in automobiles

With the rapid development of its unique advantages, nonwoven fabric has become the leading material of automotive textiles. Nonwoven fabric has become an ideal material for automobiles and replaced traditional textiles and plastic products. This paper takes a car as the research model. A DRL‐2B thermal conductivity tester was used to test thermal conductivity of the material based on the plate method. Material systems and structures of new types of heat insulation composite materials were determined according to test results and the theory of heat transfer. Then, the final new type of heat insulation material was determined by calculating and comparing average heat transfer coefficients and heat transfer between traditional insulation materials and new types of heat insulation materials. The calculated results were verified by experiments in this paper. All the test results show that the new type of composite insulation material is significantly better than traditional insulation materials, and the test results match the calculated results.     

Effect of Radiative Heat Transfer on Indoor—Fire

The importance of radiative heat transfer in the simulation of indoor-fire has been studied.Computer codeshave been developed based on four-flux model and discrete transfer model,respectively.Evaluation of the codesagainst exact analytic solution and experimental data shows that the discrete transfer model gives numericalresults with acceptable accuracy while the four-flux model underpredicts the heat fluxes although the gen-eral trend is reasonable.Numerical studies have been performed of two-dimensional,axisymmetric turbulent,buoyancy-controlled indoor fire.The computational results show that neglecting radiation in the simulationcan cause overprediction of 500K in the maximum temperature and less uniform velocity field compared to theprediction by discrete transfer model.The four-flux method has been found to produce less uniform velocityand temperature values than discrete transfer model,but is more economic in computation.     

Measurements of thermal properties of insulation materials by using transient plane source technique

The paper reports on the measuring technique and values of the measured thermal properties of some commonly used insulation materials produced by local manufacturers in Saudi Arabia. Among the thermal properties of insulation materials, the thermal conductivity (k) is regarded to be the most important since it affects directly the resistance to transmission of heat (R-value) that the insulation material must offer. Other thermal properties, like the specific heat capacity (c) and density (ρ), are also important only under transient conditions. A well-suited and accurate method for measuring the thermal conductivity and diffusivity of materials is the transient plane source (TPS) technique, which is also called the hot disk (HD). This new technique is used in the present study to measure the thermal conductivity of some insulation materials at room temperature as well as at different elevated temperature levels expected to be reached in practice when these insulations are used in air-conditioned buildings in hot climates. Besides, thermal conductivity values of the same type of insulation material are measured for samples with different densities; generally, higher density insulations are used in building roofs than in walls. The results show that the thermal conductivity increases with increasing temperature and decreases with increasing density over the temperature and density ranges considered in the present investigation.     

Thermal storage material from inertized wastes: Evolution of structural and radiative properties with temperature

Hazardous wastes, such as asbestos-containing wastes (ACW) or fly ashes (FA) resulting from municipal solid waste incineration, can be converted into inert materials using plasma torch technology. Depending on the origin of the wastes and on the cooling conditions, the materials obtained at room temperature can be glassy or partially crystallized. The aim of this work is to investigate the potential valorisation of such inertized products as sensible heat material for high temperature thermal storage in thermodynamic solar power plants. Thermal stability and optical properties have been studied from room temperature up to 1000 °C by infrared spectroscopy, differential scanning calorimetry and X-ray diffraction. All the studied materials are stable and present high total emissivity within the experimented temperature range. Their physical and chemical characteristics make of them to be good candidates for sensible heat storage materials.     

Al(H2PO4)3对玻化微珠保温材料性能的影响

研究了结合剂Al(H2PO4)3对玻化微珠保温材料抗折/耐压强度、重烧线变化率和体积密度等性能的影响。     

Thermal radiative properties of a smooth air-water interface

Thermal radiative properties for an air-water interface were calculated by considering the interface to be smooth and the water to be at uniform temperature. Monochromatic hemispherical and total normal reflectance, monochromatic and total normal transmittance, Planck mean and Rosseland mean absorption coefficients were evaluated. The wavelength interval covered by the calculations was between 0.2 and 200 μ. Other thermal radiative properties, such as emittance and absorptance, were related to the above properties, and a comparison with available results shows favorable agreement. The use of these properties in the area of remote sensing and global energy balance makes the data essential for identifying the most effective region of the spectrum and for explaining some of the naturally occurring processes where radiative transfer plays an important role.     

Silica aerogel granulate material for thermal insulation and daylighting

Silica aerogel granulate is a nanostructured material with high solar transmittance and low thermal conductivity. These properties offer exciting applications in building envelopes. One objective of the joint R&D project ISOTEG at ZAE Bayern was to develop and characterize a new glazing element based on granular silica aerogel. Heat transfer coefficients of less than 0.4 W/(m² K) and a total solar energy transmittance of 35% for the whole glazing unit were achieved. The glazing has a thickness of less than 50 mm. Another application for granular silica aerogel is, for example, in solar collectors.The thermal properties of the glazing as well as the optical and thermal properties of the granular aerogels are presented here. The solar transmittance of a 10 mm packed bed of silica aerogel was 53% for semi-translucent spheres and 88% for highly translucent granulate. In our heat transfer experiments the gas pressure, external pressure load, temperature and gas filling were varied. The various thermal conductivity values measured for the glazing and collector applications were compared to the values calculated using two different packed bed models. For the gas-dependent measurements the intergranular voids in the granulate were 1.0 ± 0.1 mm before loading the packed bed, 0.3 ± 0.1 mm at an external load of 3.2 bar (3.2 × 10⁵ Pa) and 0.6 ± 0.1 mm after release.A direct radiative conduction of λ_direct = 4.5 ± 0.5 × 10⁻³ W m⁻¹ K⁻¹ was obtained.     

机车司机室新型隔热吸声材料介绍及运用

以检验资料、使用情况为依据,详细介绍了KPB-3J憎水型轻质矿物棉复合板的容重、导热系数、释放气体分析及毒性、吸声性、防水性、工艺性、适用性等方面的良好性能特点,并与离心式超细玻璃棉板做了简要的对比,认为KPB-3J憎水型轻质矿物棉复合板值得在各型号机车、动车、城轨车辆等的司机室内推广使用。     

Thermal analysis of coupled vapor-cooling-shield insulation for liquid hydrogen-oxygen pair storage

The long-term storage of liquid hydrogen (LH₂)-liquid oxygen (LO₂) pair with extremely low heat leakage is essential for future deep space exploration. Vapor-cooled shield (VCS) is considered an effective insulation structure that can significantly reduce the heat penetration into the LH₂ tanks, however it is relatively ineffective for the LO₂ tanks. Novel coupled VCS insulation schemes for LH₂-LO₂ bundled tanks were proposed to achieve optimal performance not only for the LH₂ but also for the LO₂ tanks. A thermodynamic model had been developed and validated by experiments. The optimal VCS location, the temperature profile within the insulation, the heat leakage reduction contributed by the VCS, and the thermal performance versus scheme structural mass had been parametrically investigated. A comparison indicated that the proposed single integrated shield configuration can reduce the heat flux of the LH₂ and the LO₂ tanks by 64.0% and 54.8%, respectively compared with the non-VCS structure. In addition, the results also confirmed that zero boil-off storage of LO₂ can be achieved by only utilizing the exhausted hydrogen vapor, with no need for an extra cryocooler.     

Structure–property correlations of polymeric films for transparent insulation wall applications. Part 1: Solar optical properties

In this paper the results of a research project to establish a fundamental understanding of the physical relationships between the material structure and solar optical properties of polymeric transparent insulation (TI) materials are described. First, a systematic characterization of potential materials for TI applications in respect to their relevant physical properties in the solar radiation range was done. Second, based on the investigation of polymer films with different thicknesses model functions for the solar optical properties were established. Third, the solar optical properties were interpreted on base of polymerphysical relations. The characterization in the solar range and the calculation of solar optical film properties have shown, that the solar extinction is dominated by scattering occurring mainly at the surface. A linear relationship between the solar optical thickness and the film thickness was obtained for film thicknesses ranging from 12 to 150 μm. For various amorphous and semi-crystalline films the surface roughness correlated well with the solar optical thickness.     

Structure–property correlations of polymeric films for transparent insulation wall applications. Part 2: Infrared optical properties

In this paper the results of a research project to establish a fundamental understanding of the physical relationships between the material structure and the infrared optical properties of polymeric transparent insulation (TI) materials are described. First, a systematic characterization of potential materials for TI applications in respect to their relevant physical properties in the infrared radiation range was done. Second, based on the investigation of polymer films with different thicknesses model functions for the infrared optical properties were established. Third, the infrared optical properties were interpreted on base of polymerphysical relations. The characterization in the infrared range and the calculation of infrared optical film properties have revealed, that various functional groups of the macromolecular structure are highly absorbing. For polymers with service temperatures of about 100 °C the carbon–oxygen single bond was identified as highly effective. For 50 μm thick films a good correlation between the concentration of the functional carbon–oxygen group and the non-spectral infrared optical thickness as well as the hemispherical emittance was found. An outstanding performance profile for TI wall applications with black absorbers was obtained for cellulose based materials.     

Thermal conductivity of wool and wool–hemp insulation

Measurements have been obtained for the thermal resistance of sheep‐wool insulation and wool–hemp mixtures, both in the form of bonded insulation batts, using a calibrated guarded hot‐box. The density was 9.6–25.9 kg m^?3 for the wool and 9.9–18.1 kg m^?3 for the wool–hemp mixtures. The measurements were made at a mean sample temperature of 13.3°C using a calibrated guarded hot‐box. The estimated uncertainly in the resistance measurements was of the order of ±7%. The thermal conductivity of the samples, derived from the thermal resistance measurements on the basis of the measured thickness, was well correlated with the density, although the variation with density was larger than that obtained in previous studies. The conductivity of the wool–hemp samples was not significantly different from that of the wool samples at the same density. Moisture uptake produced an increase of less than 5% in the conductivity of the bonded wool insulation for an increase in absorbed moisture content of 20%. The thermal resistance was 1.6% lower on average for samples oriented in the horizontal plane rather than the vertical plane, but this difference is not significant. Copyright © 2005 John Wiley & Sons, Ltd.     

Aging of polymeric films for transparent insulation wall applications

A research project to develop and optimize a transparent insulation (TI) structure based on commercially available films showed, that in addition to poly(carbonate) (PC) and poly(methylmethacrylate) (PMMA) other amorphous and semicrystalline polymers such as cellulose triacetate (CTA) and poly(ethyleneterephthalate) (PET) exhibit favorable property profiles for application in low temperature systems (e.g. TI wall systems). Investigations were carried out in order to study the influence of time, temperature, humidity and solar radiation on the solar and infrared performance properties of various polymer films. Whereas the infrared properties are only slightly influenced after exposure to elevated temperatures, humidity and solar radiation, in the solar range especially extinction due to scattering increases. Detailed results are presented in the paper for four polymer film types and for TI structures made thereof. Furthermore, the results are interpreted in terms of both the molecular and supermolecular structure of the polymer films. Besides PC and PMMA films, PET and CTA films show an interesting long-term performance, being an interesting alternative to the more expensive PC and PMMA polymers.     

SLA (Second-law analysis) of transient radiative transfer processes

This paper concerns a SLA (second-law analysis) of transient radiative heat transfer in an absorbing, emitting and scattering medium. Based on Planck’s definition of radiative entropy, transient radiative entropy transfer equation and local radiative entropy generation in semitransparent media with uniform refractive index are derived. Transient radiative exergy transfer equation and local radiative exergy destruction are also derived based on Candau’s definition of radiative exergy. The analytical results are consistent with the Gouy–Stodola theorem of classical thermodynamics. As an application concerning transient radiative transfer, exergy destruction of diffuse pulse radiation in a semitransparent slab is studied. The transient radiative transfer equation is solved using the discontinuous finite element based discrete ordinates equation. Transient radiative exergy destruction is calculated by a post-processing procedure.     

电气设备常用绝缘材料特性

论述了绝缘材料对电力电子系统及设备稳定运行的重要意义,介绍了中低压电气设备在结构设计中对绝缘材料的特性要求和使用原则,对电气绝缘系统的可靠性及试验方法进行了介绍,为电气系统结构设计及使用提供参考。对常用的绝缘子、环氧树脂、热缩套管等绝缘材料进行了分析介绍,以指导中低压电气设备结构设计中对绝缘材料的正确使用。     

双层保温结构性能分析

根据保温施工经验和现场试验结果 ,提出一种既经济又能保证热力管道保温效果的保温结构设计方法———双层保温结构 ,并对其特点、施工要求进行了论述     

The influence of inner material with different average thermal conductivity on the performance of whole insulation system for liquid hydrogen on orbit storage

At present, several composite insulation systems were proposed that can be used for passive insulation systems, including foam-variable density multilayer insulation (VDMLI), aerogel-VDMLI and hollow glass microspheres (HGMs)-VDMLI. The passive insulation systems with different inner material (IM) showed different performances. However, the relationship between the average thermal conductivity of IM and the insulation performance of the whole system has rarely been investigated. It is of great significance for efficient configuration and matching of the passive insulation system. In this paper, a series of average thermal conductivity of IM were assumed to predict the insulation performance of the whole system at 20 K–300 K and high vacuum. In order to further illustrate the relationship between IM and MLI/VDMLI, the foam was replaced by the HGMs as 5 mm a unit forming a series of HGMs-foam-MLI/VDMLI insulation systems. The performance of the systems was investigated. After the foam was completely replaced by the HGMs, the performance of MLI and VDMLI systems was improved 33% and 13%, respectively. Moreover, each mode of heat transfer including solid conduction, radiation, and gas conduction for foam-MLI/VDMLI and HGMs-MLI/VDMLI insulation systems were calculated and analyzed.     

外墙外保温系统的经济实用性分析

对几种外墙外保温系统在墙体保温应用技术及工艺质量方面各自的优点与缺点、经济性、实用性、保温隔热性、防火性、保温层牢固程度、使用寿命等几个方面进行对比分析,重点分析了各外保温系统存在问题的原因,并提出相应的解决措施。