A METHOD FOR INCREASING THE SENSITIVITY OF PHASE DOPPLER INTERFEROMETRY TO SEED PARTICLES IN LIQUID SPRAY FLOWS

A method has been developed to increase the sensitivity of phase Doppl er interferometry-based particle sizing systems to small particles in the presence of a spray containing large and small droplets; an import ant consideration when using seed particles to track the gas-phase vel ocity in multi-phase flows. The method, applicable to PDPA systems con figured to operate in first and higher order refraction mode, involves doping the sprayed liquid with a dye that is strongly absorbing at th e incident laser wavelengths. This results in greatly diminished scatt ered intensity from larger droplets, thus allowing the photomultiplier gain to be set to a level sufficient to easily detect small particles without saturation. Tests conducted indicate that, at a collection an gle of 30 degrees and droplet absorptivity of gamma = 0.014/mu m, the PDPA can accurately size absorbing droplets up to approximately 200 mu m. This upper limit can be extended by changing cellection angle. Tes ts performed with an actual spray demonstrated that the method allowed detection of 1 mu m to 235 mu m droplets; more than four times the in strument's usual range of 50 : 1. A data correction scheme to determin e the effective probe volume radius for each particle size class has b een developed for absorbing particles, as standard correction schemes derived for non-absorbing droplets excessively weigh distributions tow ard smaller particles.