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Thermal Imaging Technique for Measuring Mixing of Fluids

National Renewable Energy Laboratory

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Technology Marketing Summary

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.

  • Inexpensive, fluid mixing measurement
  • Easy setup
  • Reduces measurement time
Applications and Industries
  • HVAC
  • Home energy efficiency
  • Fluid flow testing
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Patent 9,366,689
Systems and methods for thermal imaging technique for measuring mixing of fluids
Systems and methods for thermal imaging for measuring mixing of fluids are provided. In one embodiment, a method for measuring mixing of gaseous fluids using thermal imaging comprises: positioning a thermal test medium parallel to a direction gaseous fluid flow from an outlet vent of a momentum source, wherein when the source is operating, the fluid flows across a surface of the medium; obtaining an ambient temperature value from a baseline thermal image of the surface; obtaining at least one operational thermal image of the surface when the fluid is flowing from the outlet vent across the surface, wherein the fluid has a temperature different than the ambient temperature; and calculating at least one temperature-difference fraction associated with at least a first position on the surface based on a difference between temperature measurements obtained from the at least one operational thermal image and the ambient temperature value.
National Renewable Energy Laboratory 06/14/2016
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
ROI 13-19DevelopmentAvailable03/03/201403/03/2014

Contact NREL About This Technology

To: Erin Beaumont<>