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Home > Testing and Measurement > Measurement methods > Heat flux measurement

Heat flux measurement

Three methods are used at GMT for the heat flux measurement:

  • Infrared thermography
  • Thermo Sensitive Paint (TSP)
  • Flux meter

Infrared thermography

Infrared Thermography is a type of infrared imaging science. Thermographic cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 0.9-14 µm) and produce images of that radiation. Since infrared radiation is emitted by all objects based on their temperatures, according to the black body radiation law, thermography makes it possible to "see" one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature, therefore thermography allows one to see variations in temperature (hence the name).

Infrared (IR) thermography is a two-dimensional, non-contact technique of temperature measurement which can be usefully exploited in a vast variety of applications as well as wind tunnel research fields. This technique is used as a tool for thermal surface flow visualization.

This technique is available in all Onera GMT wind tunnels.

Hardware used is 1 Inframetrics camera or 1 AGEMA 880 LWB camera (available lens 7°, 12° and 20°)

Thermo Sensitive Paint (TSP)

Temperature sensitive paint is a rather new term which has arisen after the adoption of the term PSP (Pressure Sensitive Paint).

Nowadays, one thinks about TSP as a tool in wind tunnel testing using metal organic compounds like Ruthenium or Europium complexes. Their useful temperature range is from cryogenic up to approx. 400 K, so that they were not suited for high temperature measurement. This is the reason, why in former times mostly thermographic phosphors were used for measurement and why this term has become a representative for temperature sensitive paint (TSP). The working principle is the same for organic TSP and for phosphors and is based on the temperature sensitivity of their luminescent light when excited by a suited incident light source.

Principle of sensor and measurement system

The principle of temperature sensitive paint (TSP) measurement is based on the thermal quenching process of the luminescence of certain molecules incorporated into a binder matrix. Luminescence is a general term for both fluorescence and phosphorescence and the concerning molecules are called luminophores. A luminophore is activated by absorption of photons of incident light in a certain wavelength range, bringing the molecule from the ground electronic state to excited electronic states. The excited electrons return to the unexcited ground state by a combination of radiative and adiation less processes and emission occurs due to the radiative process. The wavelength of the emission light is shifted with respect to the excitation light, showing a longer wavelength.

 

 

 

Advantages and needs

  • High spatial resolution
  • Same equipment as the PSP can be used
  • No special optics, windows or cameras necessary
  • Very smooth surface finishing possible
  • Application of paint layer needed
  • Need for excitation light source and filter for lamp and camera

Onera performed heatflux measurements with TSP in a supersonic flow.

Flux meter

Onera has the capacity, during model design, to put thermocouples in the model and determine heat flux on the model surface. Function of the number of flux meter on the model, it is possible to determine a heat flux cartography on the surface.