Accurate emissivity characterisation of metals from near infrared to long wave infrared

Emissivity is a highly important, but often overlooked, characteristic of materials. It represents the efficiency of that material’s surface to radiate thermal radiation, in comparison to an ideal blackbody radiator. Different materials have different emissivity, and this is dependent on temperature, wavelength and viewing angle. Overlooking this important parameter will lead to errors within material process measurements, as well as the development of associated numerical models.

The processing of materials within the foundation industries requires an accurate measurement of temperature to ensure both material quality and process efficiency. To achieve this by the non-contact measurement approach of radiation thermometry, prior knowledge of the material emissivity is required. If the emissivity is unknown, it will lead to an incorrect reading of temperature, resulting in compromised material quality and process efficiency. Another application requiring measurement of emissivity is the emerging area of waste heat recovery within material processing. An accurate measure of emissivity is required for the development of numerical models, and, ultimately, to optimise the efficiency of energy capture.

This project will develop a test setup to accurately measure emissivity across the full infrared spectrum. The project will involve the design and creation of radiometers operating at near infrared (NIR), short wave infrared (SWIR), mid wave infrared (MWIR) and long wave infrared (LWIR). These radiometers will be used, in combination with a split tube furnace, to compare

the radiated emission from metal samples to that of a reference blackbody cavity. This capability to accurately map the emissivity spectrum from NIR to LWIR will be an invaluable tool to the aforementioned radiation thermometry and waste heat recovery applications within the metals industry.

Matthew Hobbs

University of Sheffield