Effects of photomultiplier tube voltage setting on phase-Doppler measurements

Abstract

Phase Doppler measurement devices have established themselves as an alternative to laser diffraction-based measurements for recording spray drop size distributions. In addition, phase Doppler devices also provide droplet velocities and volume flux. One limitation of the phase Doppler systems that is not discussed often in the literature is their sensitivity to the amplification voltage used on the photo-multiplier tube (PMT) detector. The correct value of voltage to use depends on the spray density, and so a calibration must be made for each spray by mechanically measuring the flux at a point in the spray. Phase Doppler output parameters (drop sizes, velocities, validation rate, and derived parameters) were measured as a function of voltage in a fixed location in a water spray. The measurements of volume median diameter were not as sensitive to the voltage setting as the volume flux measurements, which may be why the issue of voltage sensitivity is not discussed much in the literature. The contributions of the current work are: for the first time, measurements of sensitivity of DV05 and LWC to PMT voltage settings in PDI are reported, as well as the details of the different validation parameters instead of only the overall validation rate.