Simulation of sprinkler—hot layer interaction using a field model

This paper reports a study of the interaction of a sprinkler water spray with the fire‐induced hot layer using the field modelling technique. Data obtained in the large test room of the recent Swedish experiments reported by Ingason and Olsson (1992) are used to validate the results. The problem is divided into a gas phase and a liquid phase. For the gas phase, the set of conservation equations for mass, momentum and enthalpy of air flow induced by the fire is solved numerically using the Pressure Implicit Splitting Operator (PISO) algorithm. For the liquid phase, the sprinkler water spray is described by a number of droplets with initial velocity and diameter calculated by empirical expressions for the nozzle at different operating water pressures and flow rates. The trajectory of each droplet is calculated by solving the equation of motions, by including the dragging and heat transfer with the hot layer. The water droplet is assumed to be non‐evaporating and only the source terms in the gas momentum and enthalpy equations of the air flow included the interaction effects with water droplets, i.e. the ‘Particle‐Source‐in‐Cell’ method. The predicted results include the gas flow, temperature and smoke concentration field; the shape of the water spray; and some relevant macroscopic parameters such as amount of convective cooling, drag‐to‐buoyancy ratio, etc. The average smoke layer temperature and the smoke layer interface height are also calculated. The effect of the mean droplet size on those parameters is illustrated. Finally, a comparison of the water density received at floor level in cases with and without the fire is made.