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

Abstract

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).

Fire dynamics simulator technical reference guide volume 1 :

“…The amount of heat conducted away from the link by the mount is indicated by the "C-Factor", C. The RTI and C-Factor are determined experimentally. The constant C 2 has been empirically determined by DiMarzo and co-workers [95,96,97] to be 6 × 10 6 K/(m/s) 1/2 , and its value is relatively constant for different types of sprinklers. The algorithm for heat detector activation is exactly the same as for sprinkler activation, except there is no accounting for conductive losses or droplet cooling.…”

Fire dynamics simulator (version 4) :

“…The sensitivity of the detector is characterized by the value of RTI. The amount of heat conducted away from the link by the mount is indicated by the "C-Factor", C. The constant C 2 has been empirically determined by DiMarzo and co-workers [45,46,47] to be 6 × 10 6 K/(m/s) 1 2 , and its value is relatively constant for different types of sprinklers.…”

An Investigation of the Causative Mechanism of Sprinkler Skipping

“…Therefore, in the present work, an experimental study of sprinkler skipping is conducted to identify the causative mechanisms of the phenomenon. It is also expected that the testing results from this work can be utilized to assess the sprinkler models in fire simulation software [7][8][9].…”