High-speed Imaging

High-speed cameras provide the ability to capture and play back videos of the spray process, which might happen too quickly to be evaluated in real time. 

High-speed Imaging Overview
High-speed video of the spray process allows for evaluation of the transient spray characteristics, whether the area of interest is at the exit of the nozzle or near the spray target. Spraying Systems Co. uses an Olympus i-SPEED TR camera, which features a maximum frame rate of 10,000 fps, a user-friendly interface and a stand-alone video playback screen.

Method of Capturing High-speed Images

The high-speed imaging system uses a high-sensitivity, custom CMOS sensor with a high shutter speed to acquire up to 10,000 image frames per second. Images may be acquired at a pixel resolution of up to 1280x1024 (up to 2,000 fps). Typically, an external high-intensity light source is used to back-light the spray region, resulting in darkened regions where spray droplets or particles are present.

High-speed Imaging Benefits

High-speed imaging provides a unique view of the instantaneous spray distribution, concentration, shape and trajectory, and also allows for the assessment of very fast spray development. The image-based measurement makes the results mostly qualitative in nature, but the images are easily evaluated and provide a simple way to visualize the spray. However, the image’s field of view is limited, and because adequate background light is required, this instrument works best with light droplet density sprays.

Examples of the Value to Customers

High-speed imaging provides a unique combination high-temporal resolution and high-pixel resolution for visual spray evaluation. Examples of past projects using high-speed imagery at Spraying Systems Co. include transient spray development evaluation with the PulsaJet® nozzle, and overspray evaluation for surface coating.

  • PulsaJet® Spray Transients
    PulsaJet nozzles manipulate the total spray flow rate by quickly pulsing the electrically-actuated nozzle on and off with a prescribed duty cycle. However, when spraying a highly viscous material for a customer, the spray characteristics deteriorated. Spraying Systems Co. used the high-speed camera to record the spray for many cycles. During the low-speed playback, extra-large droplets were clearly observed at the start of each spray. This problem was resolved with a slight nozzle design change, resulting in a well-atomized spray during the entire spray pulse cycle.

  • Overspray Evaluation
    A customer was experiencing excessive overspray in a surface coating application. It was not clear where the overspray was originating, as the nozzle spray angle was sized appropriately for the target width. High-speed videos were acquired near the target edge, and it was observed that the spray material was only partially adhering to the target surface and the remainder was splashing off the target. By reducing the nozzle spray angle and using two side-by-side nozzles, the splash-off was nearly eliminated, reducing material costs and cleanup time.

Example Data

Hollow Cone Spray
 
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