The Drop-Size Response of the CSIRO Liquid Water Probe

Abstract

The response of the CSIRO liquid water content (LWC) device to water drops of different sizes has been investigated in a wind tunnel. Two series of experiments were conducted. The first compared the probe-measured LWC of sprays with different median volume diameters (MVD) to the LWC computed through water mass conservation considerations; the second series compared the probe LWC to that computed from the droplet spectra measured by Particle Measuring Systems' (PMS) probes. In the first series of experiments, the response was found to decrease from 100% for a water spray with an MVD of ∼ 20 μm to about 50% for a spray with an MVD of ∼ 150–200 μm. From these results, we expect that the King Probe can be used without correction for measuring the LWC of droplet distributions with MVDs less than about 40 μm. As the MVD increases, there will be a gradually diminishing response, which for MVDs of greater than 100 μm will require substantial correction. The second series of experiments produced physically unreasonable results, suggesting that the size calibration of the PMS Forward Scattering Spectrometer Probe needs to be reevalualed. These results also indicate that a correction is required for the PMS Two-Dimensional Grey Optical Array Imaging Probe.