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Thermal Imaging Technique for Measuring Mixing of Fluids

Stage: Development

There are multiple methods for measuring fluid flow. Current methods rely on different physical principles such as: pressure measurement, particle tracking using images, heat removal from a wire and Doppler shift measurements. However, infrared images are not used to quantitatively measure flow properties, fluid mixing, or mass concentration of fluids. These existing techniques for measuring two dimensional velocity fields, such as particle image velocimetry (PIV), require expensive and specialized equipment such as lasers, advanced optics and particle seeding of flows. These result in high costs, significant setup time, extensive safety measures, and may require a dedicated facility to operate. There are faster and cheaper techniques for measuring velocities such as pitot probes or hot wire anemometers; however, they provide point measurements. 

If these instruments are used to obtain two dimensional flows they become prohibitively expensive, time consuming, and have limited spatial resolution. Additionally, Laser Doppler Velocimetry (LDV) can provide high spatial resolution but is only a point measurement technique, requires many of the same expensive equipment costs as PIV, and is inadequate and time consuming for obtaining two dimensional flows and is therefore generally not used for that purpose.

Infrared thermography has been used to qualitatively determine if there are fluid flows, such as a cold spot around a hole in a building wall, but has not been used to quantify fluid flow rates or mixing.

NREL researchers have developed a new measurement technique that reduces equipment cost and time required to obtain spatially resolved two dimensional measurements of the mass fraction distribution of mixing flow streams. By using infrared thermography with advanced algorithms, two dimensional flows can be measured both qualitatively and quantitatively.

The technique invented needs only an infrared camera, inexpensive, disposable materials, and a pitot probe or other point measurement sources for speed measurements, which allows the user to take measurements at only a few locations instead of the entire flow field. Depending on the situation and accuracy required, calibration may not be necessary; however, better and more accurate measurements result from utilizing this technique with calibration.

NREL is looking to either license the technology or partner with a company to further develop the technology.

For more information, please contact Erin Beaumont at:


ROI 13-19

U.S. Patent # 9,366,689

Applications and Industries

  • HVAC
  • Home energy efficiency
  • Fluid flow testing


  • Inexpensive, fluid mixing measurement
  • Easy setup
  • Reduces measurement time


US Patent 93...9.pdf

Aug 26, 2019