Research Data - Determination of total hemispherical emissivity utilizing an in-situ calibrated, coupled experimental-simulative electron beam calorimetric approach

Abstract

The accurate determination of the total hemispherical emission coefficient (THEC) of materials is essential for modeling radiative heat transfer in high-temperature vacuum environments. This study presents a rapid steady-state calorimetric method to determine the THEC using a vacuum electron beam (EB) facility. A graphite-coated Inconel 718 foil with a thickness comparable to the electron penetration depth was used as the emission target, allowing temperature equalization within seconds. Surface temperatures were recorded via a calibrated two-colour thermal imaging system. An in-situ calibration was conducted, using the melting point of pure copper as a fixed reference. Numerical simulations were employed to validate both the emissivity determination and the temperature calibration methodology. EB heating efficiency was determined at 150 keV in a combined experimental-simulative approach using Monte Carlo simulations and backscattered electron intensity capture. Temperature calibration showed high reproducibility with a median absolute deviation of +- 0.4% and a half range of +- 1.1% at 1085 °C, and was shown to be transferable to other materials. EB heating efficiency slightly decreased from 0.832 +- 0.003 at room temperature to 0.825 +- 0.002 between 800 °C to 1140 °C. THEC values between 0.88 and 0.92 with a maximum half range of +-0.06 were obtained in the range of 840 °C to 1110 °C for graphite-coated Inconel 718 with a median roughness of Ra = 1.2 µm. Reflected radiation from the emission target and thermal losses from conduction and sublimation were assessed and found negligible. Results were consistent with literature, particularly under high surface roughness or pre-oxidized conditions.