Reflective Thermal Insulation Research Articles

Design and Experimental Evaluation of Composite Magnesium Phosphate Cement-Based Coating with High Cooling Effect

The application of surface heat reflective coatings is one of the effective measures to solve the temperature disease of concrete structures in sunlit environments. To achieve strong bonding, high durability, and good cooling characteristics, a novel inorganic reflective thermal insulation coating was prepared using magnesium phosphate cement (MPC) as the binder and reflective matrix, and titanium dioxide and glass beads as the reflective thermal insulation reinforcement functional additives. The optimum ratio of the new reflective thermal insulation coating was preferred through laboratory irradiation test, thermal conductivity test, and spectral reflectance test. The results show that MPC itself was a good reflection cooling material, and the surface and internal temperatures of concrete blocks were reduced by 7.6 °C and 6.6 °C, respectively, after using MPC as the cooling coating. When 2% titanium dioxide was added to MPC, the surface and internal temperatures were further reduced by 6.0 °C and 4.9 °C, respectively. On top of this, the surface and internal temperatures of the concrete were reduced by a further 3.9 °C and 2.2 °C when 8% glass beads were added. The bond strength of the MPCTG coating to the concrete matrix reached 2.1 MPa. Finally, the microscopic characteristics and the reflective thermal insulation mechanism of the MPCTG coating were investigated with the aid of SEM, thermo gravimetric analysis, and XRD analysis. The results show that the MPC in the MPCTG coating was well hydrated, and a large number of hydration products encapsulated the unreacted MgO particles, titanium dioxide, and glass beads, forming a dense whole with high reflection and low thermal conductivity, and the coating effectively prevented the entry of radiant heat. At the same time, the MPCTG coating was thermally stable below 70 °C. The magnesium phosphate cement-based reflective thermal insulation coating developed in this study has potential application prospects in concrete structure cooling coatings.

Novel and environment-friendly high NIR reflectance color pigments based on Fe, Pr, Ho, Nd, Er and Ce doped lithium aluminum molybdate: Synthesis and properties

This paper reports the syntheses of a series of polychromatic pigments with the general formula LiAl1-xMx(MoO4)2 (M = Fe, Pr, Ho, Nd, Er, Ce; x = 0–0.4) and the characterization of near-infrared reflectance properties. The synthesized pigments exhibited green (Pr), lavender (Nd), pink (Er) and different yellows (Fe, Ho, Ce). The XRD patterns of typical LiAl1-xFex(MoO4+δ)2 samples show that the prepared samples are triclinic lithium aluminum molybdate structures with space group P-1.The iron in the sample mainly existed in the form of Fe3+, which led to the directional growth of grains with different morphologies. The near-infrared solar reflectance (R*%) of LiAl1-xFex(MoO4)2 pigments reached 94.19%. As the doping concentration of rare earth was increased, the color of the pigments gradually deepens. By introducing rare earth elements Pr, Ho, Nd, Er, and Ce into the LiAl(MoO4)2 matrix, the color of the pigment was successfully changed from white to green, lavender, pink, and yellow, indicating that doping can control the color of the pigment. Moreover, the prepared pigments had high R*% (>87%), indicating that the pigment samples have excellent thermal insulation properties and can be used as a new type of reflective thermal insulation coatings.

Reflective thermal insulation in non-ventilated air-gaps: experimental and theoretical evaluations on the global heat transfer coefficient

The refurbishment of existing buildings represents a priority target to reduce global energy consumption. An interesting solution is represented by multilayer systems made by insulating panels mounted on a suitable frame to form non-ventilated air-gaps with the existing envelopes. This solution is attractive because it allows for renewal and energy requalification of building façades by interventions addressed exclusively to the external surfaces, without interfering with occupants. However, it produces an increase of the building volume that could be in contrast with local construction regulations. In this context, the application of reflective (low-ε) thermal insulation panels inside the air–gap seems appropriate to reduce the system thickness without penalizing the thermal transmittance of the renovated envelope. However, addressed investigations conducted on the combined convective and radiative heat transfer coefficients inside enclosures equipped with low-ε materials, are lacking. In this paper, an experimental campaign conducted in a climatic chamber by the heat flux meter method on three different samples of commercial reflective panels inside a non-ventilated air–gap has shown, for the same sample thickness, an increase of the air–gap thermal resistance up to seven times. In order to evaluate the performances on a real scale, the experimental results were employed to tune a model developed in the COMSOL environment to determine the attainable global heat transfer coefficient in real scale air cavities. The results showed that thermo-reflective panels can produce the same effect of at least 6 cm of traditional insulating materials by avoiding additional space. Moreover, useful design information concerning the attainable thermal resistance growth related to the air–gap thickness and the thermo-reflective panel emissivity, were introduced. Results showed that by setting the vertical wall height, an optimal air–gap thickness that allows for minimizing the global heat transfer coefficient, can be identified, however, this is mainly when the emissivity coefficient of the panel surfaces is lower than 0.5. Furthermore, by setting the optimal thickness, the increase of the transferred thermal flux by quadruplicating the wall height is moderate being slightly greater than 16%. By monetizing the saved volume growth, the multilayer system equipped with thermo-reflective panels is economically profitable, especially with the insulating panel cost increase and in zones where the average building value is high.

The Study on Thickness Detection Technology of Reflective Thermal Insulation Coatings for Buildings Based on Hyperspectral Technology

As a new type of building coatings, reflective heat insulation coatings have been widely used in building construction by virtue of its advantages of energy saving and environmental protection. The high and low performance of reflective heat insulation coatings directly affects the performance of building energy saving and environmental protection, and has a great impact on the indoor environment of buildings. Reflective thermal insulation coatings for buildings mainly achieve energy saving and environmental protection by reflecting and absorbing solar radiation(visible-near infrared) and building radiation(thermal infrared). For specific building reflective heat insulation coatings, the interaction between them and light mainly depends on the construction parameters, such as coating thickness. Therefore, hyperspectral technology is used to quantitatively analyze the reflection and absorption characteristics of building reflective heat insulation coatings, and to study the influence of coating construction parameters(thickness) on the performance of building reflective heat insulation coatings, so as to provide scientific and technological support for coating construction detection. With the help of hyperspectral technology, this study measured the spectral data of different coatings thickness, analyzed the evolution law of the spectral characteristics of coatings with the increase of the thickness of coatings, studied the coatings index which can characterize the thickness of coatings construction, and analyzed the correlation between the spectral data of coatings and the coatings index constructed by them and the thickness of coatings respectively. Selecting and screening the sensitive indicators of coatings construction thickness, building the thickness detection model of coatings construction, and searching for the method suitable for the thickness detection of coatings construction. The results show that:(1) the spectral data located in the 420～1 070 nm range are sensitive to the thickness of coatings 0.1～2.5 mm, and the correlation coefficient r with the thickness of coatings construction is high and phase-wise. For stability, it shows that the spectral range is sensitive to the thickness of coatings and can be used to detect the thickness of coatings;(2) Compared with the original spectrum, the coating index can effectively enhance the sensitivity of the spectrum to the thickness of coatings, and the RCI index constructed from 484 and 479 nm is the best parameter to characterize the thickness of coatings in the five categories of coatings index;(3) Among the five kinds of coatings indices, the model based on RCI index has the highest accuracy and is the best one, and its R~2=0.973, RMSE=0.185, RPD=4.018.

Thermal protective qualities of the combined material with reflective thermal insulation from aluminium foil

The article presents the results of experimental and theoretical studies of the thermal insulation qualities of foamed polyethylene with layers of reflective thermal insulation located in its thickness. Currently, the determination of the heat-protection properties of multilayer materials with reflective thermal insulation is carried out experimentally in laboratory conditions. Theoretical studies of the processes of heat transfer in the bulk of such multilayer materials and developed thermophysical model of the heat transfer process through this combined multilayer thermal insulation allowed to develop an engineering calculation method for determining the thermal resistance of multilayer polyethylene foam with reflective thermal insulation from aluminium foil, taking into account thermal conductivity and radiation. The obtained values of the thermal resistance of multilayer polyethylene of various thicknesses by calculation showed the convergence with experimental values. This indicates that reflective thermal insulation with a low emissivity of the surface, located in the thickness of the foamed polyethylene, increases its thermal performance qualities.

Characterization, calibration and validation of an industrial emissometer

Abstract. We report on the radiometric characterization and calibration of the TIR 100-2 (INGLAS Produktions GmbH, 2019) industrial emissometer. This instrument is used for handheld, on-site directional total emissivity measurements in industrial applications, e.g., the measurement of the emissivity of highly reflective thermal insulation materials. The diameter of the measurement field is determined by two different methods. The emissometer is calibrated with three different sets of low- and high-emissivity reference samples. Each calibration is validated by comparing the results of the TIR 100-2 to directional total emissivity results of the Emissivity Measurement in Air Facility (EMAF) at the Physikalisch-Technische Bundesanstalt (PTB), Berlin. Finally, the hemispherical total emissivity of highly reflective thermal insulation materials is determined using the TIR 100-2 according to the European Standard EN 12898, and, again, the results are validated with results obtained at the EMAF.

Controlled TiO2 coating on hollow glass microspheres and their reflective thermal insulation properties

Hollow glass microspheres (HGMs) have great potential in building energy-saving and industrial insulation. Anatase TiO2-modified HGMs were prepared by a sol‒gel method in acetic acid-ethanol solution. Scanning electron microscopy, X-ray diffraction, zeta-potential measurements, nitrogen-sorption measurements, and Fourier-transform infrared and ultraviolet-visible-near-infrared diffuse reflectance spectroscopies showed that the alkali modification of the HGMs greatly influenced the loading and microstructure of the TiO2 film. The TiO2 loading could be accurately controlled by ethanol addition and the TiO2 coating time. A mechanism for the TiO2 coating of the HGM surface is proposed. The synergistic action of hydrogen bonding and electrostatic forces resulted in close contact between the HGMs and TiO2 sol at pH 3.5. The effects of different TiO2 loading rates on the reflective and thermal insulation properties were studied. The near-infrared reflectance of 15.9% TiO2 coated on HGMs was 96.27%, and the inner surface temperature of the composite pigment coated on aluminum board was reduced by 22.4°C. The TiO2/HGM composite pigments exhibited excellent solar reflective and thermal insulation properties, so have potential in the construction of exterior walls and roofs.

Study on the thermal performance and design method of solar reflective–thermal insulation hybrid system for wall and roof in Shanghai

Solar reflective coating applied on roof/wall surface is becoming an important passive cooling technology for building energy efficiency. Shanghai is located in the climate of hot summer and cold winter, so the hybrid system of solar reflective coating combined with thermal insulation materials on roof/wall should be an efficient way for building energy saving. In this paper, the thermal performance and design method of the hybrid system was discussed. Equivalent thermal resistance for solar reflective coating was put forward for thermal performance evaluation and energy efficiency design for the hybrid system. Equivalent thermal resistance considers not only reflectance of the material, but also the weather conditions, demand for indoor comfort, orientation and thermal performance of base wall/roof. Equivalent thermal resistance in typical summer day and winter day of Shanghai were theoretically calculated and tested. Annual equivalent thermal resistance which integrated the benefit in summer and the penalty in winter was achieved by linear regression algorithm of simulated energy, and the results were 0.07–0.40 m2·KW−1 for wall and 0.18–1.07 m2·KW−1 for roof. This means solar reflective coating is energy saving equivalent and replaceable with 7–23 mm thermal insulation layer on wall, and 14–107 mm on roof. This method was useful and accepted in the energy efficiency design standard of Shanghai.

To the determination of heat exchange conditions near the inner surface of walls with reflective thermal insulation from aluminium foil

Materials with a low coefficient of surface radiation intensively reflect the radiant component of the heat flux and reduce heat losses through the building envelope. When designing building structures with reflective thermal insulation it is necessary to evaluate the efficiency of its application. However, at present there are no methods for calculating the value of thermal losses through external walls in the presence of reflective thermal insulation on internal surface of the wall, as well as there are no data on the values of heat transfer coefficients at the inner surface of building envelope with reflective thermal insulation. In this regard, in the climatic chambers of NIISF RAABS, complex thermal engineering studies were carried out. For this a cellular concrete wall 2,8 x1,2 m was put up into the chamber with reflective thermal insulation on the inner surface and without it. The obtained results of experimental studies, presented in the work, allowed obtaining numerical values of heat transfer coefficients at the inner surface of walls with reflective thermal insulation, and use the obtained data in further calculations.

Cylindrical cryogenic calorimeter testing of six types of multilayer insulation systems

Extensive cryogenic thermal testing of more than 100 different multilayer insulation (MLI) specimens was performed over the last 20 years for the research and development of evacuated reflective thermal insulation systems. From this data library, 26 MLI systems plus several vacuum-only systems are selected for analysis and comparison. The test apparatus, methods, and results enabled the adoption of two new technical consensus standards under ASTM International. Materials tested include reflectors of aluminum foil or double-aluminized Mylar and spacers of fiberglass paper, polyester netting, silk netting, polyester fabric, or discrete polymer standoffs. The six types of MLI systems tested are listed as follows: Mylar/Paper, Foil/Paper, Mylar/Net, Mylar/Blanket, Mylar/Fabric, Mylar/Discrete. Also tested are vacuum-only systems with different cold surface materials/finishes including stainless steel, black, copper, and aluminum. Testing was performed between the boundary temperatures of 78 K and 293 K (and up to 350 K) using a thermally guarded one-meter-long cylindrical calorimeter (Cryostat-100) for absolute heat flow measurement. Cold vacuum pressures include the full range from 1 × 10−6 torr to 760 torr with nitrogen as the residual gas. System variations include number of layers from one to 80 layers, layer densities from 0.5 to 5 layers per millimeter, and installation techniques such layer-by-layer, blankets (multi-layer assemblies), sub-blankets, seaming, butt-joining, spiral wrapping, and roll-wrapping. Experimental thermal performance data for the different MLI systems are presented in terms of heat flux and effective thermal conductivity. Benchmark cryogenic-vacuum thermal performance curves for MLI are given for comparison with different insulation approaches for storage and transfer equipment, cryostats, launch vehicles, spacecraft, or science instruments.

The measured study of natural weathering performance of reflective thermal insulation coating in hot-summer and warm-winter region

In order to study the attenuation performance of solar direct reflectance of reflective thermal insulation coating under natural weathering, we conducted a measured study on five coatings with the built natural weathering platform. After the 18-month natural weathering experiments, the color of coating templets turn undertint or black with coating layer pulverized and fallen off, some of the templets starting to crack, fall off and go mouldy. Meanwhile, the reflectance ratio of reflective thermal insulation coating decreased significantly after 3 to 6 months, the degree of attenuation of the five templets is 2% to 28%. After 18 months’ exposure to the blazing sun, the most significant degree of attenuation reached 46%. The solar direct reflectance of coating templet of the same brand remained high as before after natural weathering with an initial high solar direct reflectance

Verification of the thermal insulation properties and determination the optimal position of the reflective thermal insulation layer in the wood based envelope

Abstract To achieve thinner wood based envelope is necessary look for an alternative thermal insulation material, which will have the best possible thermal insulation properties while maintaining affordability. One such material is also reflective thermal insulation layer, but it is necessary to verify the thermal insulation properties and determine the optimal position in the wood based envelope.

Evaluation Method for Energy Saving Effect of Reflective Thermal Insulation Coatings

According to the climate and energy saving characteristics in the hot summer and cold winter zone, especially in view of requirements for thermal insulation in summer, reflective thermal insulation coatings (RTIc) are gradually applied in building energy efficiency of exterior envelope. A feasible evaluation method for energy saving effect is very important for acceptance of energy efficient building construction. In this paper, thermal resistance has been used as the evaluation index. The energy efficiency of the reflective thermal insulation coatings was investigated. Four hot boxes were applied contrast test. Based on the qualitative and quantitative analysis of electricity consumption within 36 hours and comparative analysis of heating process simulating sunlight environment, thermal resistance of RTIc can be calculated on the basis of the correlation between power saving rate and thermal resistance so that energy saving effect of RTIc can be quantitatively characterized.

Summary on the Evaluation Indicator for Thermal Insulation Performance of Reflective Thermal Insulation Coatings

Reflective thermal insulation coatings (RTIc) are applied widely in Hot Summer and Cold Winter Zone and in Hot Summer and Warm Winter Zone. A feasible evaluation method for energy saving effect is very important for acceptance of energy efficient building construction. Combining with the research on RTIc at home and aboard, series of evaluation indicators of thermal insulation performance and energy saving effect of RTIc such as solar reflectance, hemispherical emittance, temperature, thermal resistance, energy efficiency and thermal inertia were summarized and the existing problems and several suggestions were also proposed.

Innovative Superplastic Forming Based on <i>In Situ</i> Infra-Red Sheet Heating

This paper describes the research work that was performed in order to propose an innovative and low cost process route for superplastic forming of aluminum and titanium alloy sheets. The driving idea was to heat only the metallic sheet using heating elements included in the pressure chamber. Several heating configuration have been tested and equipment designs investigated. Based on experimental results and numerical thermal analysis, it was found that halogen heating lamps with a high reflective thermal insulation was the best for the upper pressure chamber, whereas low effusivity Refractory Castables materials seem optimal as low cost forming die. Energy consumption evaluation shows more than 80% energy saving in nominal titanium alloy forming. A pilot forming equipment was developed and first aluminum sheet forming trials give interesting results.