Evelyne Gehin

A simultaneous characterization of thermal conductivity and diffusivity of polymer materials by a periodic method

A periodic method is used to determine simultaneously both thermal conductivity and diffusivity of various polymer materials at room temperature. The sample is placed between two metallic plates and temperature modulation is applied on the front side of one of the metallic plates. The temperature at the front and rear sides of both plates is measured and the experimental transfer function is calculated. The theoretical thermal heat transfer function is calculated by the quadrupole method. Thermal conductivity and diffusivity are simultaneously identified from both real and imaginary parts of the experimental transfer function. The thermophysical parameters of several polymer samples (PTFE, PVDF and PA11) with different thicknesses (respectively, 5 mm, 2 mm and 300 µm) were studied and compared with values from the literature. The values identified for the thermal parameters are in good agreement with values from the literature for PTFE and PVDF samples; however, we show that the method reaches its limit for the thinner PA11 sample, owing to inadequacy of the thermal model.

Impact of Health on Particle Size of Exhaled Respiratory Aerosols: Case‐control Study

Abstract Individuals with viral infection could possibly emit an infectious aerosol. The distinction between exhaled breaths of infected and healthy individuals should facilitate an understanding of the airborne transmission of infections. In this context, the present study is aimed at distinguishing healthy individuals from symptomatic ones by the study of their exhaled breath. A setup composed of a modified hood connected to an electrical low pressure impactor, which allows for the study of a wide range of particle sizes (from 7 nm to 10 μm), has been developed in order to collect exhaled breaths. This setup has been used with seventy eight volunteers. The results obtained using Principal Component Analysis (PCA) showed that exhaled breaths of individuals without symptoms have statistical similarities and are different from those of individuals with symptoms. This separation was made by the greater proportional emission by individuals with symptoms of particles collected on stages 3 (D 50 = 0.09 μm), 6 (D 50 = 0.38 μm), 8 (D 50 = 0.95 μm), 10 (D 50 = 2.40 μm), and 12 (D 50 = 4.02 μm) of the impactor. There was not a specific size distribution obtained for the individuals with symptoms. As a consequence, further research on the exhaled breath should be undertaken with symptomatic volunteers and would require the analysis of this wide range of particle sizes.

Development and evaluation of a method for the quantification of airborne Thermoactinomyces vulgaris by real-time PCR.

Actinomycetes are ubiquitous and some can be potentially pathogenic for humans when present in the air of some working areas. Its notably the case for Thermoactinomyces vulgaris in composting facilities where aerial concentrations can reach high values of more than 10(7) CFU·m(-3). Workers exposure to these inhalable bioaerosols can be the source of various diseases. The literature reveals a lack of knowledge about risk assessment: there is neither dose-effects relationship for most agents, or threshold limit value. The objectives of this study were to develop and standardize a method to quantify workers exposure to bioaerosols. We have developed and evaluated a method to quantify airborne T. vulgaris based on DNA extraction of aerial microbial communities and qPCR. Four DNA extraction protocols were compared, and primers and a hydrolysis probe were designed for specific amplification of the target species (gyrB gene). This method was compared to traditional methods based on viable or cultivable counting by epifluorescence microscopy or plating on selective media. The method was applied on environmental bioaerosols sampled under real exposure conditions in composting plants. We demonstrate that the method to quantify T. vulgaris in bioaerosols is specific, sensitive and repeatable. We demonstrate the occurrence and quantified T. vulgaris in the atmosphere of composting facilities with concentrations ranging from 3×10(2) to 3×10(6)×m(-3).

Mechanisms of Particle Deposition in Ventilation Ducts for a Food Factory

An improved Eulerian model is proposed to predict particle deposition velocity in a typical mechanical ventilation system of a dairy food factory. For fully developed turbulent flow, the model is modified based on the three-layer model developed by Zhao and Wu (2006a), accounting for thermophoresis as well as turbophoresis, Brownian diffusion, turbulent diffusion, and gravitational settling. Based on in-situ measurements of the aerosol size distributions, particles discussed in this article were in the size range 0.3–20 μm. The measured mass concentration and the predicted particle deposition velocity were used to calculate the deposited particle mass flux in the ventilation duct. The results indicate that the effects of temperature gradients and of surface roughness should be considered in food factories ventilation ducts. For horizontal surfaces, it is shown that even a little difference between empirical and theoretical models can lead to a 2-fold difference in the predicted deposited particle mass flux. Findings of this work may help to identify the specific parameters for cleaning procedures.

Design optimisation of silicon-based MEMS sensors dedicated to bioaerosols monitoring

Due to recent paradigm changes for the monitoring of air pollution, assessing human exposure to (bio)- aerosols with low-cost sensors is expected to be of growing importance. In this context, our work subsequently investigates the development of Si-based gravimetric instruments. Thus particle-resonator interactions are considered to provide a particle detachment criteria as well as geometrical features ensuring performances both in terms of sensitivity and uniform resonator response. Analytical and numerical methods have been carried out and confronted to experimental results.

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.