P. Boulet

Water Mist and Radiation Interactions: Application to a Water Curtain Used as a Radiative Shield

A numerical simulation has been carried out on a water curtain used as a radiative shield against a source of thermal radiation. An Eulerian-Lagrangian code for the dynamics of the mist is combined to a Monte Carlo simulation of the radiative transfer in the air-droplet medium. Various attenuation efficiencies have been evaluated through comparisons on an academic reference case where multiple injections are generated on a line in order to build a water curtain. The aim of this study is to pinpoint more efficient configurations improving the radiative attenuation in saving the used water amount.

Numerical Evaluation of Radiation Extinction Coefficient Using Fractal Geometry for Vegetation Modeling

This article focuses on the accurate determination of the radiation extinction coefficient (β) for a vegetal set like a tree in the frame of forest fires. Usually, this coefficient is calculated using the De Mestre relationship, not taking into account the leaf orientation and position. In order to evaluate their role, a realistic vegetal structure is numerically created using LAI data, De Wits models, and IFS geometry. A ray-tracing method is used to simulate the radiative transfer inside the numerical tree. The results show that the leaf distribution and position cannot be neglected in β determination. The use of well-known correlations are not sufficient to predict β: over-estimations of up to 100% have been observed.

Radiative shielding by water mist : comparisons between downward, upward and impacting injection of droplets

Radiative shielding with water curtain has been studied numerically, investigating three different possibilities of droplet injection : downward, upward and impacting on a wall to be protected. The efficiency has been evaluated based on radiation attenuation predicted considering a given incident flux attenuated when crossing the area where water is injected. For upward and downward injection, a simple water curtain is considered. For the impacting spray case, a water film streaming on the wall is considered in addition to the spray (an idealized film with constant and fixed thickness for the moment). The dynamics has been imported from an Eulerian-Lagrangian simulation and radiative transfer has been addressed with a Monte Carlo method. Results show that the upward injection performs better than the downward injection due to a favoring dynamics that increases the residence time of droplets. The impacting spray could be even more efficient owing to the possible high attenuation efficiency of films, but present results still make use of simplifications on the water film falling on the wall and present promising observations require further verification.