7. Special measurement techniques

7.1 Optical techniques

Optical measurements, specially adapted to particulate media, are being used more and more. These techniques, initially used in research, are now finding their way into industrial applications. Different methods need to be applied depending on the nature of the particulate flow. Flows with very low particle loads (diluted flows) can be analyzed using VLD techniques (laser Doppler velocimetry) or image analysis (high-acquisition-frequency videography). These two types of measurement cannot be used in dense flows (as is the case with industrial beds), which are opaque to the passage of light. In this case, local fiber-optic measurement techniques are employed.