Laser Imaging

The Oxford Imaging VisiSizer is used when either the droplet / particle shape or the solid particulates / bubbles within the droplet are of interest. Examples of past projects using the Oxford laser imaging system at Spraying Systems Co. include extensive measurements with the agricultural industry, where solid particles are often intended to be contained within the spray droplets, as well as applications where the spray material is expected to cause the droplets to be non-spherical.

• Agricultural Spray with Solids Content
  Spraying Systems Co. worked with an agricultural company to determine the optimal spray nozzle parameters to obtain a target drop size with a solids-content containing material. The desired droplet sizes needed to be large enough to minimize drift, but small enough to become evenly distributed on the target. The Oxford imaging system was used to visualize the solids within the droplets, as well as tune the spray parameters to obtain the desired droplet size and velocity characteristics.

• Viscous, Non-spherical Spray Material
  The measurement of non-spherical drops can be a very difficult task. Spraying Systems Co. worked with an academic unit to determine the required spray parameters to produce spherical droplets with various rheology materials (density, viscosity, surface tension, other additives). The result was a list of required operating conditions to ensure spherical droplets using various combinations of material rheologies.

Laser imaging offers many unique benefits due to its full-frame image results; standard or proprietary image analysis may be used to determine nearly any spray characteristic. Because the laser illuminates the droplets from the back side, bubbles and / or solid content within the droplets is often distinguishable, if present. The laser imaging system is only limited in that each droplet must be visually distinguishable and is therefore best suited for low droplet-concentration sprays.

This laser imaging method uses a diffused laser light source and an in-line camera to image a small measurement volume (typically one square centimeter). The laser is pulsed to illuminate the droplets for only a fraction of a second, resulting in an instantaneous spray image. The backlit imaging method allows for clear identification of droplets or particles as they block some percentage of the laser light from reaching the camera. These images are then analyzed to recover droplet size and velocity, which is determined using two images with a known time delay between the pair. Image analysis determines sphericity, as well as a number of other spray characteristics.