Camille Solliec

Numerical and Experimental Study of a Continuous Electrostatic Smoking Process

The smoking process is a batch one with long duration processing (some hours). Deposition of smoke particles can be enhanced by electrostatic precipitation. However, a better knowledge of the fundamental physics is needed to optimize the process. We carried out experimental and numerical studies to obtain essential information on the smoke flow. First, experiments physically characterized the wood smoke. These measures lead us to study the turbulent two-phase flow using an algebraic slip model. The main coupling with electrical forces is taken into account through the slip velocity. Various assumptions were tested concerning the coupled phenomena in order to build an algorithm that is able to simulate these phenomena. Numerical resolutions are compared with data from the literature on a simple electrostatic precipitator (three wires between two plates). Simultaneously, experiments were performed on a simplified scaled-down model of the smoking process (wires and one plate). The results of particle image velocimetry show clearly that the electrostatic precipitation phenomenon is effective above a threshold voltage and is significantly influenced by geometry of electrodes. Experiments and numerical resolutions underwent a validation phase. A small-size industrial demonstrator, of which the promising results will not be discussed in this paper, was conceived by exploiting the presented works.

Numerical Study of the Flow and Mass Transfer in Micromixers

Computational fluid dynamic simulations are used to characterize the flow and the liquid mixing quality in a micromixer as a function of the Reynolds number. Two micromixers are studied in steady flow conditions; they are based on two geometries, respectively T-shaped and cross-type (⊤ and + shapes). Simulations allow, in the case of ⊤ micromixers, to chart the topology of the flow and to describe the evolution of species concentration downstream the intersection. The streamline layout and the mixing quality curves reveal the three characteristic types of flow, depending on Reynolds number: stratified, vortex and engulfment flows. Vortices appear after impingement, in the exit channel. They become asymmetrical and gain in length with an increase in Re making the flow unsteady, which induces an enhancement of the mass transfer by advection between the two liquids. In the case of cross-type micromixers, the structure of the flow is strongly three-dimensional. It is characterized by symmetrical vortices in both output channels. In the zone close to the impingement, a back flow is observed which induces strong shear stresses. The results show that the + shaped system can improve the mixing process in comparison with the micromixers having ⊤ geometry. The numerical study also allows to select the locations of the most relevant zones of study, from an experimental point of view. It will allow to choose the location of PIV planes and local non intrusive sensors, such as electrochemical microprobes, in order to experimentally investigate the flow.© 2008 ASME

Preventing Indoor Bioaerosol Contamination in Food Processing Environments and HVAC Systems: Assessment of Particle Deposition for Hygienic Design Purposes

This chapter deals with airborne particle contamination in food processing indoor environments and particularly within heating, ventilation, and air-conditioning (HVAC) systems in food factory buildings. The major types of bioaerosols encountered in the food manufacturing sector as well as the bioaerosol sampling methods are firstly introduced. Secondly, some features of air handling systems such as zoning, cleanrooms, localized air handling systems, and HVAC systems are presented. Besides, the study of particle deposition to duct surfaces from turbulent airflow is reviewed and discussed. Substantially, an original work combining industrial diagnosis and experiments at factory scale with experiments at laboratory scale is then proposed through the case study of the CleanAirNet project. The CleanAirNet project (Hygienic Design of Ventilation Duct Networks in Food Factories) aimed at producing new knowledge, models, and techniques to help control the safety of the food products through a better control of aerosol particle transport and deposition in the ventilation networks of the food industry. The different work packages of the project are presented relatively to the state-of-the-art particle deposition on duct surfaces. The methodological findings and relevant applications (e.g., a newly patented particle trapping device for air handling systems) for food industries are exposed. The CleanAirNet project was supported by the French National Research Agency (ANR) from 2008 to 2012; the project consortium was conducted by seven institutes and universities, as well as three industries from the food sector.

Characterisation of Flow and Mass Transfer in Cross Shape and T-Shape Micromixers

The understanding of physical phenomena such as flow behaviour and mass transfer performance is needed in order to develop appropriate micromixers for industrial or biomedical applications. In this work, CFD is used to characterize the flow and the liquid mixing quality in a micromixer as a function of the Reynolds number. Two micromixers are studied in steady flow conditions; they are based on two geometries, respectively T-shaped (⊤) and cross-type (+). Simulations allow, in the case of ⊤ micromixers, to chart the topology of the flow and to describe the evolution of species concentration downstream the crossing. The streamlines layout and the mixing quality curves reveal three characteristic types of flow previously reported in the literature, depending on Reynolds number: stratified, vortex and engulfment flows. In the case of cross-type micromixers, the structure of the flow is strongly three-dimensional and is characterized by symmetrical vortices in both output channels. The results show that the + shaped system can improve the mixing process in comparison with the micromixers having ⊤ geometry. The second part of the study is experimental. Two cells are constructed, for both geometries (T-shaped and cross) using square channels with 400 μm hydraulic diameter. In order to use particle image velocimetry (PIV), a system has been adapted to measure velocity fields for various channel plans at different channel depths. This allows observing the evolution of the flow and the vortices development along the microchannels. A second experimental technique, the electrochemical one involving microelectrodes implemented at several positions on the channel wall located near the crossing, has been used. The electrochemical method can locally characterize the formation of swirling flows. These two complementary experimental results will be analysed and a comparison with the CFD results will be performed.Copyright