Phase Doppler Particle Analyzers

Phase Doppler Particle Analyzers are used to measure the size of spherical particles (typically liquid sprays, but also some bubbles and solid spheres). These analyzers are point sampling devices and flux-sensitive instruments. Point sampling refers to an instrument that focuses on a portion of the total spray pattern and requires targeting several test points within the spray in order to obtain a composite sample of the spray flux distribution.

The velocity of the drops/particles can also be obtained. The laser beams of the analyzer intersect at the sample volume location. When a drop passes through the intersection region of the laser beams, the scattered light forms an interference fringe pattern. Since the drop is moving, the scattered interference pattern sweeps past the receiver aperture at the Doppler difference frequency, which is proportional to the drop velocity. The spatial frequency of the fringe pattern is inversely proportional to the drop diameter.

Our lab is equipped with two types of Phase Doppler Particle Analyzers:

• 2D Phase Doppler Particle Analyzer (PDPA)
• 2D Phase Doppler Interferometry (PDI)

“2D” implies that a 2-component velocity measurement can be made and, therefore, an axial and radial velocity vector is determined.

PDPA

The 2D – PDPA is manufactured by TSI Inc., Shoreview, MN. The PDPA uses a low-power laser that is split into four beams by utilizing a beam splitter and a frequency module. The PDPA uses an Argon-Ion, 300 mW laser which is contained and cooled within a separate unit.

PDI

The PDI is manufactured by Artium Technologies Inc., Sunnyvale, CA. The PDI provides the latest in probe volume correction (PVC) and volume flux calculation. The PDI has diode 100 mW lasers which are contained within the transmitter casing and therefore do not lose significant power prior to the measurement volume. 

The phase Doppler analyzers reject signals which do not meet a series of threshold values and validation algorithms automatically. A data analysis routine is used to convert the raw drop count into meaningful drop size distributions.

Measurement range: 0.5 to 10,000 μm.