Water Mist Suppression of PMMA Boundary Layer Combustion - A Comparison of NanoMist and Spray Nozzle Performance

摘要

Water is a multiphase fire-suppressing agent and its transport and distribution pose additional challenges that necessitate research efforts. This report compares the effects of ultra fine water mist ((caret)3 micrometers) and regular spray nozzle mist ((caret)30 micrometers) on forced flow boundary layer combustion of PMMA plate, where mist was introduced with the incoming air. With the spray nozzles, burning rate downstream was enhanced due to spray- induced turbulence, which enhanced heat feedback rate to the plate in this region. Because of the higher heat feedback rate, the downstream achieves steady state burning rate faster with mist than without mist. On the other hand, the ultra fine mist has no induced turbulence and burning rate was suppressed everywhere along the plate due to mist cooling and dilution effects. Transient burning rate downstream lasts longer in this case due to the lower heat feedback rate. Flame extinguishment is by blow-off and larger spray droplets are most efficient in achieving that.