Posté le 19 September 2023 dans News
THEMACS Ingénierie was present at the largest congress on the thermophysical properties of materials: ECTP-2023 (European Congress on Thermophysical Properties).
We presented thermal conductivity measurements at cryogenic temperatures for hydrogen storage.
We presented a new measurement device for hemispherical total emissivity at cryogenic temperature.
You can download the presentation in PDF HERE.
ECTP2023 – 22nd European Conference on Thermophysical Properties
September 10-13, 2023
Development of a test bench for measuring emissivity at low temperature for the space sector.
Jean-Pierre MONCHAU1*, Bruno BRAS, Nuno DIAS, Eliott CARMINATTI-ROUSSET, Léo RAOULT
(1) THEMACS Ingénierie, 2 bis rue Alfred Nobel, 77420 Champs-sur-Marne, France
(2) ESA, European Space Agency, Keplerlaan 1, 2200AG Noordwijk, Netherlands
*Corresponding author: monchau@themacs.fr
The scientific and technical fields requiring knowledge of the emissivity of surfaces are extremely numerous. Emissivity is essential to calculate and optimize heat exchange by radiation. The emissivity of a material strongly depends on the nature of the material; it can also depend on the wavelength, the morphology of the surface (e.g. roughness) and the temperature.
In the space industry, it is necessary to control heat exchange to maintain the thermal housekeeping within acceptable ranges. Heat exchanges between the spacecraft and the surrounding environment are only radiative exchanges. For this, knowledge of the emissivity with good precision is essential. Typical applications are radiators, Multi-Layer Insulation materials, and other thermal-control surfaces, which frequently operate at cryogenic
temperatures.
There are few devices capable of measuring emissivity at low temperature (T<77K) with sufficient precision. THEMACS Engineering on behalf of the European Space Agency (ESA) has developed a measuring bench to measure the emissivity on any substrate. At these temperatures, reflectometric methods for high emissivity are difficult to use because the useful spectral range is between 10 and 200µm and the reflected flux is low. Consequently, a calorimetric approach is usually more feasible and provide lower uncertainties. The measurement bench is inspired by existing devices [1-3] with the novelty of not needing to produce a specific sample geometry. For this we made a fluxmeter made with an emissive surface at a temperature slightly higher than the sample to be tested. To maintain it at a constant temperature, it is supplied with an electrical power that is continuously measured. The advantage of this approach is that it does not have to regulate the temperature of the sample. Another advantage is to be able to cool down quickly. The fluxmeter is painted with an emissive paint which must be characterized at all temperatures. The first results allowed us to adapt the design in order to significantly lower the level of uncertainty for measurements on different types of materials.
Significant references
1 The total hemispherical emissivity of painted aluminum honeycomb at cryogenic temperatures, J.Tuttle and all, Advenced in Cryogenic Engineering, AIP Conf. 1573,590-596 (2014)
2 Measurement of the total hemispherical emittance of different surfaces at temperature from 4K to 200K, Jamotton and all, Proceeding oft he sixth European Symposium on space environemental control systems, ESA SP-400, 1997
3 A high-resolution measurement of the low temperature emissivity of ball infrared black, J. Tuttle, Edgar R. Canavan, Michael DiPirro, et al., AIP Conference Proceedings 1434, 1505 (2012)
