A new model to predict the activation time of fire suppression sprinklers is validated experimentally. The model extends the range of applicability of previous formulations to allow for the presence of water droplets in the fire plume. The presence of wate droplets in the hot gasf flow is due to the activation of the first sprinkler. The droplets are carried by the gas and deposited on the surrounding sprinklers, where they evaporate. The vaporization process cools the sprinklers and this cuases a delay in their activation. Three sets of commercially avilable sprinklers are tested under three different boundary conditions. The experimental results show good agreement with the predictions of the model within the uncertainies associated with the measurements. The influence of th sprinkler frame orientation on the evaporative cooling is also discussed in this paper.
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