Imaging measurement techniques

  Schlieren visualization Copyright: © WSA High-Speed-Schlieren- Visualization of spray evaporation

At the Institute of Heat and Mass Transfer visualization techniques like the PIV-Method or High-Speed-Visualization are used for studying the high dynamic processes in multi-phase flows. One example for multi-phase flows is the direct injection in engines. Our experience shows that the High-Speed-Visualization with continuous light sources is a poor method for the visualization of high dynamic multi- phase flows. To resolve the microscopic time scale of a high dynamic multi- phase flow we use a monochromatic pulsed high speed light source in combination with a High-Speed-Camera or a Double-Frame-Camera. Often it is also necessary to make processes like the evaporation visible. This goal we reach with combination of our high-speed visualization system with a Schlieren visualization system.

Far-field microscopy is often used for researching the microscopic multi-phase flow regimes. Driven by the conviction that local resolutions for the visualization of the smallest structures in present researches are too low, we at the Institute of Heat and Mass Transfer developed a transmitted light microscope. The images which are taken with this microscope include information about the shape, size, number and speed of structures with local resolution which was not reached until now. Since you can only visualize the contour in optically dense objects with such microscopy techniques, you get little information about the internal structure of the object. The Ballistic Imaging is a possible method to reveal the internal structures for optically dense sprays. As one of the few institutions worldwide, the Institute of Heat and Mass Transfer uses the Ballistic Imaging to visualize high dense sprays.

Measurement techniques

  • Transmitted light microscopy
  • Ballistic Imaging
  • High-Speed-Visualization
  • Schlieren visualization
  • PIV

Measured Variable

  • Macroscopic spray geometry
  • Microscopic spray structure
  • Droplets and ligaments
  • Phase boundaries
  • Microscopic and macroscopic spray velocity
  • Flow field
  • Evaporation