Numerical studies on the interaction of sprinklers and the hot layer

At least four mechanisms can be identified to explain the interaction between sprinkler and fire in an enclosure: The direct cooling of the burning objects; the cooling of the hot layer; the pre-wetting of the walls, floors and neighbouring objects; and finally the displacement of oxygen from the fuel. This paper reports the interaction of the sprinkler water spray with the hot layer. A field modelling technique is used and the problem is divided into gas and liquid phases. For the gas phase, the set of conservation equations for mass, momentum and enthalpy is solved numerically using the PISO algorithms. For the liquid phase, the sprinkler water spray is described by a number of droplets with initial velocity and diameter calculated by empirical expressionsfor the nozzle at different operating water pressures andflow rates. The predicted results include the gas flow, temperature and smoke concentration fields; the shape of the water spray; and some relevant macroscopic parameters such as amount ofconvective cooling, drag to buoyancy ratio etc. The effect of the mean droplet size on those parameters is illustrated.