3D Mapping of the Sprinkler Activation Time

Abstract

Sprinkler activation is one of the key events defining the course of a compartment fire. The time when activation occurs is commonly used in the determination of the design fire scenario, which is the cornerstone of the design of building fire safety features. A well-known model of sprinkler activation (response time index (RTI) model) was introduced into the numerical scheme of the ANSYS Fluent computational fluid dynamics (CFD) package. The novel way in which the model is used is the calculation of the time for sprinkler activation within each discrete cell of the domain. The proposed novel approach was used in a case-study to assess the effects of comfort mode natural ventilation on a sprinkler’s activation pattern. It was found that hinged vents in the comfort mode had a significant effect on sprinkler activation, both in terms of delaying it as well as limiting the total number of cells in which the sprinkler would have activated. In some scenarios with a hinged vent, no activation was observed in the central point of the vent, possibly indicating problems with the autonomous triggering of the fire mode of such a device. It was also found that the RTI and C (related to the conductive transport of sprinkler fitting) parameter values had a moderate influence on sprinkler activation time—only for high-temperature sprinklers (≥ 141 °C). This study shows the applicability of the 3D activation time mapping for research focused on the fire safety of sprinkler-protected compartments and for the performance-based approach to sprinkler system design. Even though the RTI model is the industry standard for the determination of sprinkler response, the model implementation in ANSYS Fluent was not validated. This means that sources of uncertainty, mainly connected with the determination of flow velocity and temperature are not known, and the model should be used with caution. An in-depth validation is planned for subsequent studies.

A Study on the Reliability of Modeling of Thermocouple Response and Sprinkler Activation during Compartment Fires

“…After the calculation is finished, one can retrieve data for any cell in the domain or prepare 2D or 3D maps of suitable variables. Furthermore, the same analysis can be simultaneously performed for multiple sprinkler types and thermocouple bead dimensions without any significant increase in the computational cost, as shown in [11]. This can be used by the designers of sprinkler systems.…”

“…Under certain circumstances (e.g., in the presence of automatically activated natural vents) a sprinkler system laid out according to standardized guidance might not provide optimal protection, and it could be beneficial to be able to assess the layout using numerical simulations of different fire scenarios. Węgrzy ński et al developed a methodology that allows for identifying the locations of sprinkler head placements based on 3D activation maps [11]. Furthermore, since sprinklers are usually mounted just beneath a compartment ceiling, the temperature distribution in this region has a crucial significance for proper activation as well [12].…”