A Prototype Probe For Direct Measurement of the LWC in SLD Clouds

This paper presents experimental results that were obtained with a prototype probe designed to measure liquid water content (LWC) in Appendix C and SLD icing cloud conditions. The LWC probe consisted of a total pressure probe, a water collector to ‘trap’ ingested water droplets, and a suction fan to provide a controlled volumetric airflow. Water droplets were collected iso-kinetically by the probe, and the LWC was determined from the water mass and volumetric air drawn into the probe. A water collector was developed that made use of a combination of hydrophobic fiber mesh, water adsorbent paper and desiccant materials to store the ingested water droplets. However, the water absorbed by the desiccant material was difficult to ascertain hence the dessicant material was removed from the water collector and a humidity sensor was installed inside the probe. The performance of the prototype probe was evaluated in a laboratory by injecting a known quantity of water directly into the probe inlet and comparing this to the amount adsorbed by the water collector. The results showed that the mean collection efficiency of the LWC probe was 92.1 ± 8.3% for an LWC range of 0.2 to 1.9 g/m³. A method for computing LWC from the relative humidity measurements inside the probe and the water collected by the water collector was developed and tested.