Phase-doppler interferometry with probe-to-droplet size ratios less than unity. I. Trajectory errors.

Phase-Doppler interferometry in which a probe volume that is much smaller than the droplets being measured has been shown to work well when coupled with a phase-ratio and intensity-validation scheme that is capable of eliminating trajectory-dependent scattering errors. With ray-tracing and geometric-optics models, the type and magnitude of trajectory errors were demonstrated quantitatively through stochastic trajectory calculations. Measurements with monodispersed water droplet streams and glass beads were performed to validate the model calculations and to characterize the probe volume. Scattered-light intensity has also been shown to provide a robust means of determining the probe cross-sectional area, which is critical for making accurate mass flux measurements.

Phase-Doppler interferometry with probe-to-droplet size ratios less than unity. II. Application of the technique.

Practical limitations associated with the use of small probe volumes with respect to the droplet size that is being measured by the phase-Doppler interferometry technique are discussed. An intensity-validation scheme and corresponding probe volume correction factor have been developed that reject trajectory errors and account for the rejections in calculation of the probe cross-sectional area. The intensity-validation scheme also provides a tractable method of setting the photomultiplier tube gain and laser power. Volume flux measurements in dilute sprays have shown a significant improvement over those made by standard phase-Doppler interferometry techniques at small beam waist/droplet size ratios.

Response characteristics of the phase Doppler particle analyzer for sizing spherical particles larger than the light wavelength.

A theoretical model, based on the geometrical optics approach, has been developed to simulate various aspects of the phase Doppler particle analyzer (PDPA). The model has taken into consideration the nonuniform (Gaussian) illumination of the particles as they pass through the measurement probe volume. Instrument response curves have been generated for various scattering angles by performing spatial and temporal integration of the scattered intensity distribution over the receiver surface. Experimental and theoretical investigations have established the applicability of this instrument to both forward scattered and backscattered angles.

Sizing fine particles with the phase Doppler interferometric technique.

A theoretical model based on the Lorenz-Mie theory was used to study the response characteristics of the Aerometrics phase Doppler particle analyzer (PDPA). The validity of the model was verified experimentally, and its suitability for calculating measurement uncertainties was established. The theoretical and experimental results suggest that size resolutions of the order of +/-0.3 microm are possible when the PDPA is used to measure small spherical particles (< 10 microm). We show that the optical configuration of the PDPA plays an important role in establishing the sizing uncertainty of the instrument.