Numerical Studies On Sprinkler-Hot Layer Interaction

Abstract

This paper describes how sprinkler water spray would interact with a fire-induced hot layer. The field modelling technique is used and the problem is divided into gas and liquid phases. Experimental results reported by Walton and Budnick were used to verify the predicted results. 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 iprinkler 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 flowrates. The trajectory of each droplet is calculated by solving the equation of motions, taking into account the dragging and heat transfer with the hot layer through which it travels. The water droplet is assumed to be non-evaporating, and the convective heat transfer coefficient is fitted by an empirical equation. Only the source terms at the gas momentum and enthalpy equations included the interaction effects with water droplets, that is, 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, and so on. Effect of the mean droplet size on those parameters is illustrated in this paper.