Numerical simulation for the a priori evaluation of the efficiency of stand-alone purifier in an office - Application to formaldehyde

This study deals the elimination of formaldehyde present in air of weakly ventilated office by the installation of a purification stand-alone device functioning by photocatalytic oxidation. The process consists first in absorbing gaseous formaldehyde present in indoor air to oxidize it in carbon dioxide and water by UV irradiation. The working of this photoreactor can lead to the almost complete degradation of formaldehyde. The aim is to determine the device efficiency in terms of exposition according to the ventilation parameters of the room (air change rate, pollutant emission rate), the reactor characteristics (geometry, size, flow rate, efficiency) and its position. The simulated system is a furnished office in which a surface source of pollutant and a purification device are placed. The conservation equations for momentum, mass and energy are solved using numerical simulation software Fluent® in steady-state. Numerical simulations provide access to the velocity and concentration fields in the volume. This approach allows also to identify dead zones, where pollutant accumulates, and short-circuits in the studied system. For the different cases, the average concentration reached in steady-state is compared to the concentration without purifier to determine the reduction rate. The results of the work reveal the influential parameters for the design and the setting up of a stand-alone purifier. This study should eventually define the criteria for correct positioning of the device in relation to the air inlets and outlets of the room. These simulations also allow to define the range of optimal flow rate for a proper operation of the reactor in order to prevent risks caused by formaldehyde exposure. This work is a part of a study which aim is the design and the realisation of a purification device for indoor air, alternative to ventilation (high energy-consuming). The purification capacities of the reactor will be evaluated in a test room, where conditions are controlled, and compared to the results of numerical simulation.