Numerical study of the transient two-phase flow within sprinkler fire protection systems

Abstract

In the present study, the transient air and water flow within a full-scale sprinkler fire protection system filled with pressurized air at idle state (dry pipe) was investigated. Computational Fluid Dynamics (CFD) simulations within the OpenFOAM package were carried out to calculate the air/water flow inside the pipes consequently to the opening of one sprinkler head, accounting for the discharge of air through the sprinkler head, and the inflow of water from a fire pump. A VOF (Volume of Fluids) approach was followed, accounting for the compressibility of air, and turbulence was considered using the k-ε realizable model. Furthermore, pump and sprinkler routines were implemented, taking into account the pump performance curve and the phenomenon of choked flow at the sprinkler head when the exit velocity reaches sonic conditions. Various scenarios were studied, i.e. opening of the sprinkler head before pump activation (also known as single interlock) or opening of the sprinkler head after pump activation (double-interlock). In particular, the time constant of the system, i.e. the time necessary to reach steady-state water flow at the sprinkler head required was assessed for systems of gridded typology under various operating conditions (different initial pressure values in the system).