A Mathematical Model of the Drag Component of a Sprinkler Spray Adjacent to Horizontal Smoke Vents

A mathematical model has been developed to investigate the effect of a sprinkler spray on adjacent horizontal smoke venting and in particular the water droplet drag component. The pressure difference across a roof vent and the volumetric flow of smoke vented are determined by considering the interaction between the drag force of the sprinkler spray and the buoyancy of the smoke layer in the spray region. Smoke venting may become progressively more inefficient as the sprinkler operating pressure increases due to the cooling and drag effect of the sprinkler spray. Full scale experiments were carried out to validate the model. Results show that the mathematical model can predict the observed trend of a decrease in vented volumetric flow with an increase in sprinkler operating pressure, which eventually leads to ineffective smoke venting. Experiments with different smoke venting areas show that vent area has little influence on smoke flow once sprinkler pressure causes a loss in smoke flow efficiency or vent function.