An accurate instrument for emissivity measurements by direct and indirect methods

Abstract

Emissivity is a quantity essential to consider when assessing the measurement uncertainty in non-contact temperature measurements. This paper presents a new instrument for measuring emissivity of opaque materials from 200 °C to 450 °C in the spectral range of 2.1 to 2.5 µm. These ranges are ideal for measuring the temperature of metals, such as aluminium, during manufacture or heat-treating processes. The instrument consists of a pair of hemispherical cups coated with Vantablack® and gold respectively, a custom designed radiation thermometer, and a hot plate. This instrument enables both the direct and the indirect methods for measuring emissivity of materials. Use of two identical cups allowed for quantitative analysis of the uncertainty of the instrument to determine the most suitable emissivity measurement range. The expanded uncertainty of the instrument was lower than 0.058 (k = 2) over the entire measuring temperature range. Studies were undertaken using different materials with emissivities ranging from 0.06 to 1. These included aluminium alloy 6082, stainless steel 304, and HiE-Coat 840M paint. Relative uncertainty analysis indicated that the indirect method was more accurate for measuring low-emissivity materials, whereas the direct method was more suitable for all other materials. Our instrument, with experimentally determined measurement uncertainty, aims to offer accurate emissivity references for use in radiation thermometry applications.

Investigation of Biomass Fouling on Screw Feeder in Preconversion of Pyrolysis

“…The radiative heat transfer rate was calculated using eq based on the Stefan–Boltzmann law. Q rad ( n ) t res = ε n − 1 σ A n / ( n − 1 ) ( T n − 1 4 − T n 4 ) + ε n − 2 σ A n / ( n − 2 ) ( T n − 2 4 − T n 4 ) where t res is the residence time of a wood particle at each section with a nominal value of 0.6 s, ε 0 is the emissivity (0.38) of stainless steel (screw feeder alloy) assuming the amount of heat absorbed by the wood particles is equal to the heat emitted from the screw feeder, ε n is the emissivity of pine wood particles (0.924) for n ≥ 1, σ is the Stefan–Boltzmann constant (5.67 × 10 –8 W/m 2 K 4 ), T 0 is the temperature of the screw feeder, and T n is the temperature of the n th layer of wood particles.…”

“…where t res is the residence time of a wood particle at each section with a nominal value of 0.6 s, ε 0 is the emissivity (0.38 17 ) of stainless steel (screw feeder alloy) assuming the amount of heat absorbed by the wood particles is equal to the heat emitted from the screw feeder, ε n is the emissivity of pine wood particles (0.924 18 ) for n ≥ 1, σ is the Stefan−Boltzmann constant (5.67 × 10 −8 W/m 2 K 4 ), T 0 is the temperature of the screw feeder, and T n is the temperature of the nth layer of wood particles. Upon the combined conductive and radiative heat, the temperature increase of a wood particle in the nth layer passing one section on the screw feeder can be calculated by normalizing the thermal energy by the pine wood particle's mass (m) and specific heat capacity (C, 2300 J/kg K 16 ), as shown in eq 3.…”

A Comparative Review of Thermocouple and Infrared Radiation Temperature Measurement Methods during the Machining of Metals

“…The cameras must be appropriately calibrated using approximate black-body calibration sources and also by defining emissivity coefficients for a range of temperatures, as the measurements are dependent on the emissivity of the material [109,110]. In the literature reviewed, most researchers assumed the material emissivity to be a constant value, which led to the introduction of uncertainties and errors in their measurements.…”

Special Section on TEMPMEKO 2019: a feature on the XIV International Symposium on Temperature and Thermal Measurements in Industry and Science & IV International Temperature Conference, Beijing (TEMPMEKO & TEMPBEIJING 2019) and Metrology for Meteorology and Climate (MMC 2019)

“…A paper by Webster et al [15], included in this special feature, looks into a low-cost, robust, and easy-to-use temperature marker based on organic phase change materials in the temperature range of 1 • C to 7 • C for agricultural, medical and food storage applications. Zhu et al [16] describe an emissivity measurement apparatus in the wavelength range of 2.1-2.5 µm utilizing two hemispherical cups, one coated with gold and the other with vertically aligned carbon nanotube black coating. The uncertainties are evaluated through simulation and the performance is demonstrated by experiment.…”