THE INTERACTION OF SPRINKLER SPRAYS AND FIRE PLUMES
Link, Eric D.
Marshall, Andre W
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The critical factor for successful suppression using fire sprinklers is the delivery of water to burning surfaces. Water delivery is dependent on initial spray characteristics and subsequent spray interactions with the opposing fire plume, which can deflect or reverse the sprinkler spray away from the targeted fire source. Measurements provide a comprehensive validation data set for computational fluid dynamics (CFD) spray models, as well as insight and engineering guidance to the spray-plume interaction important in fire sprinkler applications. An experimental facility consisting of an array of four sprinklers, similar to that of typical suppression system installations, is used to evaluate both quiescent spray dispersion and spray-plume interaction conditions. A 0.2 m x 0.2 m centrally located forced air jet, with velocities ranging up to 4 m/s is used (in place of a fire) to provide a well-characterized, repeatable kinematic challenge to the spray. Measurements include quiescent case spray dispersion and local volume flux delivery to the plume source to evaluate spray penetration through the plume. Additional measurements include air jet centerline drop velocity and drop size at variable source injection velocities to evaluate plume penetration behavior. These spray dispersion experiments capture the dominant transport physics and kinematic behavior of the spray plume interaction. Scaling analysis of the spray plume interaction is explored for two regimes of spray penetration; individual drop action and group spray action. In the individual drop action regime the droplets have a negligible effect on the plume and penetration scales with the ratio of drop terminal velocity to plume velocity. In the group action regime, a spray work criterion is proposed, accounting for drag interactions with the plume. The complete set of spray dispersion and plume penetration measurements comprise a data set of high resolution and well-characterized boundary conditions (including detailed initial spray measurements for each sprinkler in the array) useful for CFD validation.