Papers by Keyword: Emissivity

Abstract: In this study, low-thermal emissivity coatings were developed using aluminum leafing particles dispersed in an acrylic binder. The aluminum particles were modified through a ball milling process to enhance their leafing properties, with milling times ranging from 5 to 15 h. The effects of milling time on particle size, morphology, and leafing degree were examined using scanning electron microscopy (SEM) and laser diffraction analysis. Coatings with different particle volume concentrations (PVC) and thickener contents were prepared, and their thermal emissivity was evaluated. Results showed that milling time significantly affected the leafing behavior of the aluminum particles, with longer milling times leading to improved dispersion and lower emissivity values. The addition of a thickener enhanced particle distribution, but excessive concentrations resulted in void formation due to hindered solvent evaporation. The lowest thermal emissivity was achieved at a milling time of 15 hours and 10% PVC, providing valuable insights for the design of effective low-emissivity coatings for thermal management applications.

Abstract: Tantalum carbide (TaC) coating, produced in an ultrahigh temperature chemical vapor deposition (CVD) process, exhibited high thermal and chemical stabilities, low emissivity, and high purity. Low emissivity of 0.3~0.43 was measured on TaC coating at 1000°C and compared with the one of SiC coating. As revealed in both simulation and experiment, the low emissivity of TaC coatings not only improves temperature uniformity in the SiC PVT process, but also reduces power consumption in both SiC crystal growth and GaN epitaxial deposition. The results provide important guidance to process tuning when switching from a conventional graphite or SiC-coated component to its TaC-coated counterpart.

Abstract: Laser powder bed fusion (LPBF) is a frequently used manufacturing process due to its advantages in lightweight construction, design possibilities and functionalization of geometry. However, the printed parts will often have to undergo time and cost expensive non-destructive testing by sophisticated methods like X-CT. Thus, there is a strong demand to identify suitable online process monitoring techniques that allow to reduce or substitute post-process NDT effort. The temperature field reacts sensitively to deviations during processing, thus online temperature monitoring is a promising approach. In the present work a spatially resolved temperature measurement, based on 2-channel-pyrometry, is used for process monitoring in LPBF. The camera system is coaxially integrated into the beam guidance of the LPBF system. The coaxial observation enables a lateral resolution better than 10 μm over the whole build-up area of 250 x 250 mm2. Single tracks were welded with different parameters and observed by the camera system to identify thermal indicators. Metallographic cross-sections of the tracks were compared with the melt pool width measured by the online observation system. The deviation was ca. 3 %. In addition, cubes of 10 mm by 10 mm by 10 mm are built up. The melt pool area is identified as useful indicator for the process behavior and for the first time the assessment of part density is demonstrated in LPBF during process by the help of a thermal monitoring system.

Abstract: La_0.8Sr_0.2MnO₃ was prepared to investigate the infrared emissivity of the sample under 0.76-2.5 μm and 2.5-500 μm infrared fields. The sample exhibited characteristic peaks of rhombohedral perovskite structure at 298-318 K, and split of the main peak weakened with increasing temperature. Intensity of the ferromagnetic resonance peak enhanced with increasing temperature, and the peak was shifted toward high magnetic field. A weak paramagnetic resonance peak appeared at 318 K, indicating that ferromagnetic-paramagnetic transition was occurring. The temperature of the sample under 2.5-500 μm field was higher than that under 0.76-2.5 μm. The emissivity of the sample increased with radiation time under 2.5-500 μm, but it had no obvious changes at about 0.665 under 0.76-2.5 μm. The emissivities at the same temperature fields were higher than those under 0.76-2.5 μm and 2.5-500 μm fields, respectively. It suggested that 0.76-2.5 μm and 2.5-500 μm radiations had inhibition effect on emissivity of La_0.8Sr_0.2MnO₃.

Abstract: Radiation leaving the solid surface provides an important reference for detection in both military and civilian areas. In this paper, total radiation leaving a solid plate is calculated with different emissivities considering the environment radiation. The results prove that a lower emissivity of the surface material has a stronger reflection of irradiance from the Sun, and therefore may enhance the total radiation leaving the plate. This is different from most cases where a lower emissivity always leads to a smaller radiation effects. The emissivity of material coated to the solid surface should be properly chosen according to the detailed surrounding environment as well as the radiative properties of the solid parts in order to achieve a minimum radiation effects.

Abstract: This work compares thermal colour and emissivity of different pigments printed on to two types of jersey knitted fabrics (cotton and polyester). In order to analyze and differentiate the thermal colours of the knitted fabrics samples, diurnal and nocturnal thermal images of a female body were captured in an outdoor environment using a thermal imaging camera. Five pigments (white, black, yellow, magenta and cyan blue) were analyzed in a conditioned environment, simulating atmospheric (diurnal/nocturnal) and skin temperature, using a climatic chamber, a thermal manikin and a thermal imaging camera. The thermal tests allowed identifying the thermal colour of the printed pigments for application in the diurnal thermal camouflage garments.

Abstract: The work is devoted to effective and ecological technologies for the application of functional structured materials for roads, railways, airfields on permafrost with forced cooling of the sub-soil foundation. The physical and mathematical simulation of the thermal state of frozen ground with single and double-layer coatings was performed. The temperature profiles of a model combine roadbed on the longstanding permafrost have been calculated at winter conditions of the Northern Hemisphere. This roadbed include an upper surface coating with low thermal conductivity and high emissivity in the long-wavelength IR range at convective-radiative heat exchange. The second high-conductive subsurface coating is laid on the underlying sub-soil and ensures its cooling as the “heat pump”. The efficiency of the proposed technology of roadbed construction based on the use of non-toxic waste of numerous industrial productions. The carried out research will be in demand for the specialists of transport support, engineering glaciology, in the field of climatology, oceanology, construction, environmental measures, and also in the presentation of financial and economic forecasts of the prospects for the development of polar and subpolar regions, the Arctic and the Antarctic, and high-mountain.

Abstract: High emissive Ca²⁺/Fe³⁺-doped LaAlO₃ based ceramic materials were prepared by flame spraying and controlled crystallization method. The phase composition, microstructure, infrared optical properties of Ca²⁺/Fe³⁺-doped LaAlO₃ based ceramic powders were investigated. The physical mechanism for the significantly enhanced infrared emissivity of LaAlO₃ by doping with Ca²⁺ and Fe³⁺ was analysized. This high emissive Ca²⁺/Fe³⁺-doped LaAlO₃ based ceramic materials shows promising applications in high temperature thermal process field to enhance the radiative heat transfer and improve its thermal efficiency.

Abstract: Thermal insulation effect of reflective insulation is based on the reflection of thermal radiation. Reflective insulations are mainly used in combination with the non-ventilated air cavity. Proposed paper deals with experimental measurements of the thermal insulation properties of the air cavity surrounded by low-emissivity surfaces and comparison of measured values with calculated values according to the standardized procedures. The beginning for determination of the thermal resistance of air cavity was to conduct several experimental measurements by Hot Box method using heat flow meter. The results show good agreement between measured and calculated data.

Abstract: An exact measurement of the disc brakes car temperature present difficulties, because the higher thermal stress is produced on the shiny metallic surface, which are in movement and in sliding contact with the brake pads. If an infrared camera is used for the thermal evaluating of the disc brakes, an important factor that must be considered is the reflected temperature. The aim of this research is to study the modification of the reflected temperature in correlation with the disk brake temperature and to establish a relationship for the estimation of this variation.