Droplet sizing interferometer

A two-component phase Doppler interferometer (PDI) was used to determine droplet size, velocity, and number density in spray flames. The data rates were determined according to the procedure discussed in [5]. Statistical properties of the spray at every measurement point were determined from 10,000 validated samples. In regions of the spray where the droplet number density was too small, a sampling time of several minutes was used to determine the spray statistical characteristics. Results were repeatable to within a 5% margin for mean droplet size and velocity. Measurements were carried out with the PDI from the spray centerline to the edge of the spray, in increments of 1.27 mm at an axial position (z) of 10 mm downstream from the nozzle, and increments of 2.54 mm at z = 15 mm, 20, 25, 30, 35, 40, 50, and 60 mm using steam, normal-temperature air, and preheated air as the atomization gas. 

Droplet size may be determined with the use of a laser interferometer. This technique is an extension of the laser Doppler anemometry (LDA) technique commonly used to measure velocities of small particles in a flowing stream. Two equal-intensity Gaussian beams are made to intersect at their focal waists to form a standing electromagnetic wave distribution in the intersection (probe) volume. This standing wave can be visualized conceptually as a set of planar fringes perpendicular to the... 

Capability to Measure Small Changes in Droplet Size. Several experiments were performed to assess the capability of the interferometer/ visibihty technique to measure drop size changes resulting from changes in the atomization procedure or from subsequent drop evaporation. Using... 

Comparison of the Visibility/Interferometer Techniqiie with the MgO Collection Technique. During one experiment, using kerosene as the primary fiuid, a MgO-coated microscope slide was used to collect droplets 40 in. from the nozzle. The impressions formed by the droplets in the MgO were then viewed and sized using an optical microscope. During the same experiment and at the same location, drop sizes were measured using the visibility technique. One hundred drops were analyzed using each technique, and comparisons were drawn. 

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