The Effect Of Evaporative Cooling On The Activation Time Of Fire Sprinklers

Arrays of fire sprinklers are installed in buildings to protect the property and their occupants against the damages of fire. When a fire occurs, the sprinkler closest to the fire location typically activates first and releases water droplets into the rising plume of hot gases. Part of these droplets is entrained by the plume and may impact on adjacent sprinklers providing evaporative cooling and thus delaying their activation. The current model that simulates the thermal response of fire sprinklers does not include this evaporative cooling effect; therefore, a new model is proposed to extend the applicability of the previous formulation. The new model includes one parameter, determined experimentally, that is associated to the evaporative cooling effect. Commercially available sprinklers are tested to assess the accuracy of the proposed model for a range of conditions (hot gas temperature and velocity, water volumetric fraction and sprinkler orientation with respect to the flow).