Particle Shape and Aspect Ratio Effect of Al2O3–Water Nanofluid on Natural Convective Heat Transfer Enhancement in Differentially Heated Square Enclosures

The present numerical investigation, based on the finite volume method, deals with the characterization of flow and thermal fields inside differentially heated square enclosures filled with Al₂O₃–water nanofluid. The study focuses on the effect of shapes and aspect ratios of nanoparticles (NPs), depicted by Rayleigh number (Ra), solid volume fraction (?), and enclosure on both flow and heat transfer enhancement. Streamlines, isotherms contours, and velocity profiles as well as the average Nusselt number are considered. Results found show that the heat transfer rate increases with Rayleigh number as well as with nanofluid volume fraction. For the six different examined cases of NPs’ aspect ratios, nanofluid with oblate spheroids NPs (d_p = 0.13) was found to engender a significant enhancement in the overall heat transfer. In addition, heat transfer rate was more pronounced at great values of aspect ratios of NPs for prolate spheroids. Results also showed that heat transfer enhancement decreases as the Rayleigh number increases independently of the considered enclosure, shapes, and aspect ratios of NPs.     

Kinetic Study of Hindered Amine Light Stabilizer Photografting in Poly(propylene) Films under Natural Weathering and Accelerated UV Conditions: Effect of Additive Concentration

Full Paper: The objective of this work is aimed at determining the kinetics of HALS photografting in PP films as a function of the additive concentration under both natural weathering and accelerated UV conditions. The stabilizer studied had a single structure that combined HALS and a UV absorbing unit detectable at 308 nm in the UV spectrum of PP, capable of inducing a photoreaction with the polymer matrix. The kinetics of HALS photografting on PP films at various additive concentrations was determined by direct spectroscopic measurements on film samples through the absorption band of the stabilizer positioned at 308 nm in the UV spectra, which was attributed to the highly conjugated methylenic double bond. The content of free HALS was determined as a function of exposure time by UV spectroscopy for all the additive concentration ratios used. It is shown that the kinetics of HALS photografting increase with a decrease in the additive concentration ratio. The whole grafting process under conditions of natural weathering occurred in the PP film after almost 350 h of exposure, while approximately 20 h were necessary under accelerated UV conditions. Moreover, these kinetics are well described by a third order polynomial model, validated by a maximum value of the coefficient of correlation close to unity. This was also confirmed by a comparison of the time values measured at 50% of the total grafting calculated from the model with those observed experimentally. This finding was consistent with the data obtained on the free HALS content determined by UV spectroscopy.

The percentage of HALS photografting in PP films as a function of time under natural weathering, determined by UV spectroscopy.     

An optimal open-loop multimode fiber gyroscope for rate-grade performance applications

We report the realization of a new version of a fiber optic gyroscope (FOG), using low-cost multimode fiber components. This is achieved by an optimal choice of the components such as fiber, coupler, light source and photodetector. The aim behind this work is to demonstrate the versatility of the low-cost multimode FOG for rate-grade performance applications. Both analog signal processing and open-loop operation are used in the proposed FOG experiment. The obtained sensitivity is ∼7°/h and the angle random walk is about 0.087°/. The influence of the coupler technology on the performances is investigated.     

Improved efficiency of multicrystalline silicon solar cells by TiO2 antireflection coatings derived by APCVD process

This paper reports about the adaptation of the chemical vapor deposition (CVD) thin films technology to the fabrication process of multicrystalline silicon solar cells as a simple, low cost and very effective technology for efficiency device improvement by reducing reflection and improving the light-generated current. In this contribution, the higher reflection of a mc-Si solar cell surface is strongly reduced by the deposition of TiO₂ antireflection coating (ARC) on the front using the atmospheric pressure chemical vapor deposition method (APCVD). The surface morphology and elemental composition of the TiO₂ antireflective layers were revealed using scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy . The reflectivity was then reduced from 35% to 8.6% leading to the increase of the short circuit current J_sc which was 33.86 mA/cm² with a benefit of 5.23 mA/cm² (surface area=25 cm²) compared to the reference cell (without ARC). This simple and low cost technology induces a 14.26% conversion efficiency which is a gain of +3% absolute in comparison to the reference cell. The LBIC measurements of a typical multicrystalline cell confirmed the uniformity of the photocurrent distribution throughout the device. These results are encouraging and prove the effectiveness of the APCVD method for efficiency enhancement in silicon solar cells.     

Fracture analysis of rubber‐like materials using global and local approaches: Initiation and propagation direction of a crack

In this work, fracture of elastomers is analyzed using global and local approaches, combining experiments, analytical developments, and finite element calculations. The J‐integral is chosen as a global parameter characterizing crack initiation in such materials. Particular attention is paid to single specimen methods for measuring the fracture surface energy. More precisely, models developed in the literature are summarized and, because of the lack of accuracy of these models, an original pertinent expression of J is proposed by analogy with linear elastic fracture mechanics frameworks. However, the J‐integral is not able to predict the kinetic or the propagation direction of a crack. Thus, some local parameters are examined: principal strains, principal stresses, and the strain energy density (SED) factor. Results revealed that all these parameters represent reasonable indicators of the crack propagation direction in elastomers. Moreover, unlike maximal principal stress and SED factor, maximal principal strain seems to govern the crack initiation in this kind of materials. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Numerical study of the influence of diesel post injection and exhaust gas expansion on the thermal cycle of an automobile engine

This study deals with the development of a numerical tool developed to analyze the thermomanagement of the heat rejection from the fuel combustion in the case of a four cylinder 2 L – 110 HP direct injection Diesel engine. It is composed of two main elements: the first one simulates all the phenomena linked to the combustion, the second one is about thermal exchanges in the heart of the engine. We only deal with the first one here.The combustion study is based on two aspects: the consideration of multi injection (the pilot injection, the main injection and the post injection) and the simulation of compressible flows through the exhaust valves.This model allows us to predict the combustion chamber energy balance (heat fluxes, mechanical work) and the fuel consumption with an experimental tolerance within 3%. Engine tests have been made at the laboratory to validate this result.Fuel consumption calculation is linked to the accurate estimation of the exhaust gas flow and temperature. The main interest of this method is that it takes into account the sonic blockage at the exhaust valve opening.This work has also allowed to precise the post injection importance during the engine temperature rise. The increase in thermal rejects is used to accelerate the warm up of the different engine fluids.     

Thermal field in SOFC fed by hydrogen: Inlet gases temperature effect

In the present work, the effect of the hydrogen and the air temperature values on the temperature distribution in a Planar Solid Oxide Fuel Cell is studied by the aid of a two-dimensional mathematical model. Two different configurations of the Solid Oxide Fuel Cells are examined: i) the Anode Supported Planar Solid Oxide Fuel Cell (ASP_SOFC) and ii) the Electrolyte Supported Planar Solid Oxide Fuel Cell (ESP_SOFC). In order to describe the temperature distribution within the SOFC, the coupling of the mass and energy transport phenomena along with the electrochemistry is required. The studied parameters are: a) the hydrogen and the air temperature values and b) the geometry configurations. The complex system of the governing equations is numerically solved with the finite differences method and the calculation of the temperature distribution within each domain of the SOFCs is calculated via the 2-D mathematical model processed by FORTRAN language. Finally, the mathematical model predictions for the temperature distribution under the influence of the studied parameters are thoroughly discussed.     

Study of species, temperature distributions and the solid oxide fuel cells performance in a 2-D model

A two-dimensional mathematical model for a planar SOFC (solid oxide fuel cell) is constructed. The distribution of the chemical species, the temperature and the performance (power) and the current density were calculated using a single-unit model with double channels of co-flow pattern. The finite volume method was employed for the calculation. The method was based on the fundamental conservation laws of continuity, momentum, energy and mass. The equations are implemented in FORTRAN language. The effects of several heat sources and flow rates on the calculated results were also investigated. The reference SOFC polarization curve has been calculated by imposing a uniform temperature of 800 K, a pressure equal to 1 atm; H₂ and O₂ molar fractions equal to 0.97 and 0.21 respectively. Results of temperature, chemical species distributions, performance and efficiency under several heat sources are shown and discussed. At a current density of about 23500 A/m², the power densities under all sources and chemical sources reached their maximums of 12965 W/m² and 16209 W/m² (i.e. 25% lower) respectively. However the temperature increment in the anode is analyzed toward all sources and chemical reaction. The temperature maximum values for each heat source type reached 1005.81 K and 984.69 K respectively.     

Personal monitor glass badge: theoretical dosemeter response calculated with the Monte Carlo transport code MCNPX

This paper describes the results of the simulation of a radiophotoluminescent (RPL) dosemeter with the Monte Carlo transport code MCNPX. The aim of this study is to calculate the response with MCNPX of the RPL dosemeter in terms of equivalent doses H(p) (0.07) and H(p)(10) using X-ray photon radiation qualities N series, together with S-Cs and S-Co nuclide radiation qualities, specified in ISO 4037-1. After comparison with reference values versus experimental results, the deviation of the theoretical responses of the RPL dosemeter proved to be lower than 5 % for reference values and lower than 10 % for experimental results. This good correlation validates the model over the energy range studied.