Researchers at the TU-Darmstadt have developed a new technique to measure the size and velocity of droplets and particles in a flow. The new method measures reliably also non-transparent particles and droplets of suspensions or emulsions. Industrial application areas include primarily diagnostics in processes such as spray drying, spray painting or in the food industry. The characterization of droplets and particles in a flow is a central diagnostic problem for many research and development tasks; however conventional techniques are largely unsuitable for processing non-transparent particles or particles with solid content such as suspensions. Researchers at the Institute of Fluid Mechanics and Aerodynamics at the TU-Darmstadt have improved existing time-shift technique to enable reliable size and velocity measurements of such particles.
Moreover, the new developments have led to a more compact instrument realization at significantly lower investment costs. Implementation of the optical technique can be in either a forward or backscatter configuration, allowing easy adaption to any particular measurement task. Hence, the instrument offers significant advantages for utilization in an industrial environment.
Proven in the lab and now undergoing extensive verification tests, is also the ability to measure refractive index with the instrument. This offers a means of distinguishing between species and/or phases, for instance identifying water droplets and ice crystals in mixed glaciated spray conditions. The measurement principle of the time-shift technique is based on light scattered by particles from a highly focused light sheet of specific intensity profile. Either one or two detectors register the scattered light, which, because of the light sheet intensity profile, will be function of time and particle velocity. The nature and time features of the received signal on the photodetectors can be directly related to size and velocity of the particle, knowing beforehand the relative refractive index. By using two detectors, redundancy offers the further option of estimating refractive index.
The TU-Darmstadt will present the new measurement technique at the Achema 2012 in Frankfurt from 18 to 22 June (Hall 9.2, Stand A66).
