A NEW CRITERION FOR STABILITY OF SMOKE LAYER UNDER SPRINKLER SPRAY

A model has been developed for the interaction of the buoyant smoke layer and the sprinkler spray. Based on the theoretical analysis, the ratio of the maximal drag force of unit area 0D and the maximal buoyancy force of unit area 0B in spray region is proposed as a new criterion for predicting the stability of smoke layer under sprinkler spray. For validating the criterion, the sprinkler operating pressure and the smoke temperature are measured by using an experiment system located at the PolyU/USTC Atrium for sprinkler spray-smoke layer interaction. 0D and 0B are calculated by 3rd-order Simpson method. The experimental results show that the smoke layer remains stable when the 00 / BD ratio is less than 1, and a downward smoke plume which represents the instability of the smoke layer forms when the 00 / BD ratio is more than 1. The driving force of the down- flow is the difference between 0D and 0B. KEYWORDS sprinkler spray; instability of smoke layer; interaction of smoke layer and sprinkler spray; drag force; buoyancy forc