Emissivity measurement of PbLi droplets in a vacuum for heat recovery by radiation

•The emissivity of a liquid lithium-lead droplet is verified by infrared thermal imaging.•An measurement is performed using 0.8 mm diameter droplets at 400℃ with a velocity of 3 m s−1.•Three H2 gas pressures are applied to verify the effect of incident hydrogen molecules.•The obtained emissivity are 0.35 ± 0.06, 0.33 ± 0.06, and 0.36 ± 0.06.•The incident H2 molecules have no effect on the emissivity.