A review on the applied techniques of exhaled airflow and droplets characterization
Merghani, …
Thématique: QAI
Measurement of pore size distribution of building materials by thermal method
N. Dujardi …
Thématique: OPTIMISTHE
Novel in situ measurement methods of the total heat transfer coefficient on building walls
A. Françoi …
Thématique: OPTIMISTHE
In situ quantitative diagnosis of insulated building walls using passive infrared thermography
M.H.A. Lar …
Thématique: OPTIMISTHE
Measurement of pore size distribution of building materials by thermal method
The present work focuses on the study of the thermophysical properties of low porous insulation materials. In peculiar, we investigate the pore structure of composite materials and cements by thermal method. This method, adapted for fragile materials, is based on an existing model which allows the determination of pore size distribution. Firstly, the existing analytical model is presented. The thermal conductivity is modeled by assimilating the studied medium to N fluid phases and one solid phase in series / parallel. Secondly, some extensions to this model are proposed. In particular, we show that in the case of a single pore size, it is possible to obtain a finer pore size distribution by means of a normal law. We also show for the first time that the normalization of the thermal conductivity is an interesting way to study the pore size distribution of a material without knowing the overall porosity rate (which strongly depends on the method used). Furthermore, this model and its extensions have been successfully applied to different kinds of materials (plant fiber composites and cements). Fibers reinforced composites have one class of pores around 30 – 60 lm. Chemical treatments do not affect this pore size. Cements show a macroporosity (around 20 lm) which is often underestimated.
Thématique: OPTIMISTHE
Abstract High energy consumption in the building sector appeals for the implementation and the improvement of innovative approaches with low-environmental impact. The development of eco-friendly composites as insulating materials in buildings provides practical solutions for reducing energy consumption. Different mass proportions (2.5%, 10%, and 20%) of untreated and chemically treated palm fibers were mixed with (cement, water and sand) so as to prepare novel composites. Composites were characterized by measuring water absorption, thermal conductivity, compressive strength and acoustic transmission. The results reveal that the incorporation of untreated and chemically treated date palm fibers reduces novel composites’ thermal conductivity and the mechanical resistance. Thermal measurements have proved that the loading of fibers in composites decreases the thermal conductivity from 1.38 W m−1 K−1 for the reference material to 0.31 W m−1 K−1 for composites with 5% of treated and untreated fibers. The acoustical insulation capacity of untreated palm fiber-reinforced composites (DPF) was the highest at 20% fiber content, whereas treated palm fiber-reinforced composites (TPF) had the highest sound insulation coefficient for fiber content lower than 10%. Compressive strength, thermal conductivity and density correlation showed that only chemically treated fiber-reinforced composites (TPF) are good candidates for thermal and acoustic building insulations.
Thématique: OPTIMISTHE
Measuring the administered dose of particles on the facial mucosa of a realistic human model.
Duan, M., …
Thématique: QAI
Cracks in silicon photovoltaic modules: a review
Photovoltaic cells are considered as one of the most critical components in photovoltaic systems for they convert the sunlight photons into electricity. However defects on the surface of the photovoltaic cells have a detrimental effect on them. Thus, research focuses on one hand on the degradation caused by the cracks namely on their impacts on the efficiency of photovoltaic modules and on the other hand on the techniques which are used to spot them. The main objective of this review is to inquire on the impact of the microcracks on the electrical performance of silicon solar cells and to list the mostused detection techniques of cracks.
Thématique: OSED
Paraffin/ Expanded Perlite/Plaster as Thermal Energy Storage Composite
The use of thermal energy storage composite materials allows passive cooling and heating in buildings, yielding substantial energy savings. The purpose of this study is to develop and test a new phase change material (PCM) composite by loading expanded perlite (EP) with paraffin (RT27) to form plaster composites. The leakage tests allowed to unfold the optimal RT27 loading rate. To avoid paraffin leakage out of the composite structure, a waterproof product, Sikalatex® (SL), was used to coat the RT27/EP composite before mixing it with plaster. Thermal properties of RT27/EP/SL integrated in plaster were assessed. The effect of aluminum powder insertion on enhancing the composite thermal properties, was investigated. Paraffin loading rate was 60% by direct impregnation. FTIR analyses proved that the produced composites showed a good chemical compatibility between different components. DSC analyses revealed that composites have suitable energy storage capacities of 51.57 ± 0.01 and 49.95 ±0.15 kJ.kg-1 for RT27/EP/SL and RT/EP/SL/Al, respectively. These composites are suitable for indoor temperature regulation. Thermal cycling tests showed a good thermal stability of plaster PCM composite. Thermal conductivity of plaster composite containing 50% wt of RT27/EP/SL/Al composite was increased by 80% and 68% at 12°C and 40°C respectively compared with the aluminum free composite.
Thématique: OPTIMISTHE
Numerical Simulation of GaAs Solar Cell Under Electron and Proton Irradiation
Though gallium arsenide (GaAs) solar cells are proven to be relatively stable in space working conditions, they are prone to the effects of aging, which deteriorate their characteristics. The lifetime of solar cells is restricted by the degree of radiation damage that they receive. This important factor affects the performance of solar cells in practical applications. The aim of this article is to investigate by numerical simulation on the influence of aging on the main characteristics of GaAs solar cells in the space. Degradations of the electrical characteristics are simulated for over a period of 15 years. The atmosphere (AM0) conversion efficiency decreases with time from 19.08% for the unirradiated cells to 10.38% in 15 years of the mission in space. Even with low doses of particle irradiation, the performance is significantly reduced subsequent to usage over the period of 15 years of the mission in space. Numerical simulation results also reveal that the short-circuit current, the open-circuit voltage, and the conversion efficiency decline gradually with time. Moreover, the calculated evolutions are in good agreement with the measured behaviors of GaAs-based solar cells embedded in geostationary satellites during the Navigation Technology Satellite 2 (NTS-2), the Engineering Test Satellite V (ETS-V), and the NAVigation Satellite Timing And Ranging (NAVSTAR) missions, which substantiate the introduced aging law accounting for both the cumulated doses of particles and the different electron and hole traps in the structure.
Thématique: OSED
Are VOCS an efficient way to detect fungal development in maize grains?
Aleksic, B …
Thématique: QAI
Impact of the aging of a photovoltaic module on the performance of a grid-connected system
Photovoltaic systems belong to the green energy dynamics which is an ambitious program based on energy efficiency and sustainable development. In this study, the impact of the aging of a photovoltaic module is investigated on the electrical performance of a grid-connected system. A photovoltaic conversion chain with MPPT (Maximum Power Point Tracking) control and LC (Inductor-Capacitor) filter is modeled and dimensioned according to the grid constraints. A method of hybridation detection of the MPPT coupling long-time aging evolution and short-time determination is proposed. Aging laws for the electrical and optical degradations of the photovoltaic module are introduced for the long-time evolution. Results display the lowering of the maximal power point with a rate of 1%/year and a slight augmentation of the THD over time even though it remains inferior to the IEEE standard STD 19-1992 maximum value of 5% for a usage of 20 years. Moreover, an equivalent scheme for the additional electrical resistance engendered by the aging of the photovoltaic module regarding other resistances of the photovoltaic system is given. Finally, the elevation of this resistance by 12.8% in 20 years may have non-negligible consequences on the power production of a large-scale installation.
Thématique: OSED
The present work focuses on the study of the thermophysical properties of Posidonia Oceanica natural fibers in order to investigate the potential of their use as loose-fill thermal insulation material in the Mediterranean construction. 24 samples were prepared. Bulk densities were varied from 17 kg m-3 to 155 kg m-3. Chemical alkali treatments with various conditions were applied to these fibers. The influence of treatments and of density on morphological and thermophysical properties of samples was evaluated. The surfaces were examined by using scanning electron microscopic. The thermal measurements were performed with the Hot Disk thermal constants analyzer. Results have shown that thermal conductivity decrease when density decreases until an optimum. After that, it increases as the density is reduced. Furthermore, regarding thermal conductivity, it was found out that the effect of chemical treatment is not significant mainly at the low densities. A very slight improvement was found at high densities with treated fibers, mainly the treatment that consists of immerging fibers twice in 2% sodium hydroxide solution during 2 h at 80 °C. Higher mass heat capacity was observed with this same treatment. Additionally, it was revealed in this study that Posidonia-Oceanica fibers have thermal conductivity and thermal diffusivity close to conventional insulation materials and higher mass heat capacity that reached 2533 J kg-1 K-1.
Thématique: OPTIMISTHE
Aerosol mass concentration measurements: Recent advancements of real-time nano/micro systems
Soysal, U. …
Thématique: QAI
Fan H., Li …
Thématique: QAI