Dropwise evaporative cooling of a low thermal conductivity solid

Insight on extinguishment of a solid fuel fire by sprinkler generated droplets is obtained by detailed modelling of a single droplet evaporative cooling on a hot low thermal conductivity solid. The assumption of constant and uniform temperature at the solid-liquid interface, which decouples the solid and the liquid modellmg, cannot be applied to this case because strong local cooling of the solid requires the solutions of both regions (liquid and solid) to be coupled. The large thermal gradients observed at the edge of the droplet preclude the application of finite difference techniques for the integration of the transient conduction governing equation. A mixed technique that uses a control volume method for the liquid and a boundary element formulation for the solid is proposed. Both methods are briefly outlined and the computed predictions are validated with experimental measurements which encompass high resolution thermography of the solid surface subjected to evaporative cooling. Insight on the temperature distribution at the solid-hquid interface is obtained deduced from the model and the deviation from the constant and uniform temperature at the liquid-solid interface is assessed. The radial versus axial conduction in the liquid droplet is also quantified.