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).
A model for the prediction of dropwise evaporative cooling over hot solid surfaces is proposed for the case of radiant heat input. A detailed representation of the droplet shape during the transient is provided. The direct radiant contribution to the evaporative process is expressed as a liquid-vapor interfacial term and a constant heat absorption term within the liquid layer. The liquid layer is treated with a onedimensional heat conduction approximation justified by previous results and three submodels are used to describe it during the transient. A boundary element method for the solid thermal behavior, previously developed, is extended to this case. The results obtained from a closed-form solution, with simplified solid-liquid interfacial boundary conditions, are also included. Comparisons with the experimental data illustrate the adequacy of the model and the performance of the closed-form solution.
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