Performance of a Monofiber Optical Probe in Determining the Droplet Size and Velocity in Spray Systems Compared with a High-Speed Camera

Abstract

The ability of a monofiber optical probe to characterize the hydrodynamics in spray systems was compared with that of a high-speed camera. Initially, the performance of both techniques was determined on the same droplets by using a syringe to produce a series of droplets. The optical probe gave a discrepancy according to the high-speed camera mainly due to the fact that the image processing of the high-speed camera photos determined the velocity from the movement of the droplet centroid while the optical probe determined the interfacial velocity from its collision with a droplet. The droplet oscillation occurred since the droplet formation process and droplet coalescence on the probe eventually led to the discrepancy. However, when comparing both techniques statistically, their results were not apparently different. Secondly, a full-cone industrial nozzle was used to provide the spray. The average velocities from the two characterization techniques were then in close agreement; the oscillation and coalescence effects became insignificant due to less dense, the smaller sizes and the higher velocities of the droplets. However, the collision on the probe tip was off center and the difference in size limits still caused the discrepancy, especially for the size distribution. Nevertheless, a major advantage of the optical probe is that it is capable to determine the droplet hydrodynamics in dense spray conditions and enable the direct determination of the local liquid fraction, one of the important characteristics of a spray system.

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“…Diameters were determined by evaluating the area A (m 2 ) of each particle on 300 images. The area of the droplet was obtained through the common image analysis procedure . From this area, equivalent diameters were calculated, assuming that particles were spherical Once an equivalent diameter had been associated with each droplet of the spray, an average diameter for the spray was determined using the Sauter diameter definition .…”

“…The area of the droplet was obtained through the common image analysis procedure. 25 From this area, equivalent diameters were calculated, assuming that particles were spherical…”