Fire Safety Science Digital Archive

A phase Doppler particle analyzer (PDPA) was used to screen candidate water mist nozzles for use in a scaling validation aimed to allow scaled-down testing of water mist systems. Proper configuration of the PDPA remains somewhat of an art due to a lack of definitive guidelines for the many user-defined setup and data regression options. To validate the setup, a custom-designed iso-kinetic sampling probe (Probe) was developed to independently measure water mist fluxes at the same locations as the PDPA measurements. Using the Probe as a guide, the optimal PDPA operation parameters can be determined expeditiously for reliable measurements. To provide input to numerical modeling of water mist sprays, gross drop size distributions in terms of cumulative volume fraction were conventionally derived from local drop size distributions and water flux measurements and fitted using a composite of Rosin-Rammler and log-normal distributions. However, it was found that the accuracy of the data fit in the lower drop size range can substantially affect the conversion accuracy to the gross drop number distribution required by numerical modeling. This issue can be resolved by deriving the gross drop number distribution directly from measurements, or by ensuring a sufficiently accurate data fit in the lower drop size range if converted from the cumulative volume fraction.