Determination of Emissivity by Using Reflected Thermal Radiation
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The determination of emissivity is crucial in any temperature measurement using radiation thermometry. Without this knowledge, large measurement uncertainties result. There is a lack of information on emissivity for common materials. Where there are databases, these databases often give emissivity for a specific material in a range or give emissivity for different conditionings of the material. This information may not apply to certain uses of the material. This creates quite a bit of doubt for anyone making measurements in the field. What is needed is a method to determine emissivity for a material object in the field. In 2011, Yamada and Ishii discussed a method that was set up in a fixed geometry to determine the emissivity of a specular object. In this paper, a method is discussed to determine the emissivity of both specular and diffuse objects using a thermal radiation source. The theory is presented. Then, practical measurements which were made are discussed. These measurements are compared to emissivity determined by other methods.Keywords:
Low emissivity
Thermal Radiation
Void (composites)
Thermal Radiation
Reflection
Diffuse reflection
Radiation properties
Low emissivity
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In order to verify the heat dissipation characteristics of selective low emissivity materials, the traditional low emissivity materials and selective low emissivity materials were coated on the oxidized steel surface, and the heat transfer model between the target and the dark room was established. Finally, the heat dissipation characteristics of selective low emissivity materials were simulated, and the effects of the emissivity and the darkroom temperature on the heat dissipation characteristics of selective low emissivity materials were analyzed. The results showed that for high temperature targets, selective low emissivity materials had better heat dissipation characteristics than traditional low emissivity materials. The lower the emissivity in mid-far infrared bands, the better the heat dissipation characteristics of selective low emissivity materials. When the ambient temperature of the dark room fell from 30°C to -30°C, the lower the temperature, the better heat dissipation characteristics of selective low emissivity materials.
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Determination of the surface temperature and emissivity of glossy materials is a complicated task due to the relatively wide range of emissivity values and the reflection of infrared radiation from surrounding objects. As a consequence, standard methods used in infrared thermography are not applicable. In this article, an alternative method is proposed for the measurement of the surface temperature and emissivity of glossy materials used in the external structures of buildings that is based on an external source of thermal radiation. It is shown that the method gives quite accurate values of emissivity of both low- and high-emissivity glossy materials, whereas the surface temperature of low-emissivity glossy materials is less accurate and strongly depends on the accuracy of the used thermal camera.
Low emissivity
Thermography
Thermal Radiation
Reflection
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Low emissivity
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Abstract Generally, commercial textiles show high mid-infrared emissivity and the thermal radiation accounts around 50% of the heat loss. However, conventional clothes usually increase the thickness to reduce the heat conduction without considering lowering the mid-IR emissivity. Thus textiles with reducing infrared emissivity for passive radiative heating offer an energy-free way to keep human body warm. Herein, we reduced mid-IR emissivity of the textiles by covering Ti 3 C 2 T x MXene sheet on the cotton fabric through dip coating. MXenes as a new family of two-dimensional (2D) materials shows strong absorption in visible and near-IR regions and strong reflection in mid-IR region. Through simple and scalable method of dip coating, we fabricate four samples with different MXene content from 0.05 mg/cm 2 to 0.20 mg/cm 2 with 0.277∼0.431 mid-IR emissivity. This material and preparation method can be used for personal thermal management on traditional clothing.
Low emissivity
Textile
Thermal Radiation
MXenes
Reflection
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This chapter contains sections titled: Background High Emissivity Coatings Commercial High Emissivity Coating Update Benefits of Using High Emissivity Coatings Factors Adversely Affecting the Evaluation or Performance of High Emissivity Coatings High Emissivity Coating on Owens Corning Insulation Furnaces Future Directions Acknowledgement
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Infrared emissivity is one of the most important factors for the temperature measurement by infrared thermography. Although the infrared emissivity of an object can be measured from the ratio of blackbody and the object, at room temperature it is practically difficult to measure the value due to the background effects. Hence, quantitative reflectance of bare steel plate and the surface of coating was measured by FT-IR spectroscopy and emissivity was calculated from this. The emissivity of polished bare steel surface was from 0.06 to 0.10 and the value for the unpolished bare steel can not be achieved because optical characteristics changes of surface roughness induces erroneous results. Emissivity of transparent paint coated steel was from 0.50 to 0.84. Depends on the IR absorption regions, which is a characteristic value of the coating, emissivity changes. This study suggests surface condition of material, thickness, roughness et cetra are important factor for IR optical characteristics. Emissivity measurement by reflection method is useful technique to be applied for metal and it with coating applied on the surface. The range of experimental errors of temperature can be narrowed by the application of infrared thermography from the measured thermal emissivity.
Low emissivity
Black-body radiation
Reflection
Thermography
Thermal infrared spectroscopy
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Based on the calculation model established in this paper, the radiation temperature of a thermal target attached a thin film on its surface was calculated during sun exposure. From the results, stealth effects of the film with different parameters of the emissivity were investigated. For a thermal target, the low emissivity film has a good stealth effect in 8~14μm. However, due to the influence of solar radiation, it is difficult to achieve stealth in 3~5μm by using a low emissivity film alone. Then some other methods, such as insulation, cooling and so on, have to reduce the radiation of the thermal target for infrared stealth in this band. Moreover, these methods can also reduce the radiation of the thermal target in 8~14μm, so requirements for the emissivity of stealth film in this band can be lowered.
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Thermal Radiation
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Under precondition of high emissivity,the thickness of high emissivity ceramic coatings should be reduced to satisfy the requirement for mechanical property,which can also save raw materials and decrease the weight of the apparatus.So the relationship between emissivity and thickness of the coatings is important.In this paper,the coatings were prepared from Al2O3 sols and high emissivity fillers by spin and spray processes,respectively.The relationship between emissivity and thickness of coatings was examined,and the critical thickness of coatings was determined while the emissivity changes with the thickness rapidly.Based on Maxwell-Garnett theory,a new theoretical model about the relationship between emissivity and thickness of composite coatings is established.The emissivity values from the theoretical calculation are agree with the experimental data,which shows that the model can be used to predict the emissivity or the critical thickness of the composite coatings.
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