Effect of Operating Parameters on the Heat Transfer and Liquid Film Thickness of Revolving Heat Pipe

This paper presents a study on the effects of operating parameters on the liquid film thickness and heat transfer of revolving heat pipe. The effects of speed, radius of rotation, evaporator and condenser temperatures, and mass of the working fluid are considered. Also, the effects of these parameters on the maximum heat transfer and minimum mass of the working fluid supplied to the heat pipe are considered. A simplified theoretical model is presented to estimate the heat transfer and the liquid film thickness. The theoretical model is used to determine the driven forces on the control volume. The system of equations associated with the heat pipe model is solved using the fourth-order Runge–Kutta method through a numerical code written in MATLAB. The results show that the heat transfer increases by decreasing the mass of the working fluid and increasing the temperature difference through the heat pipe. They also show that the liquid film thickness increases with the decrease in temperature difference and with increase in the mass of fluid. The maximum heat transfer increases with the increase in the rotation speed. The minimum mass of the working fluid supplied to the heat pipe increases with the increase in temperature difference and with the decrease in the rotation speed.     

Importance du facteur lithologique sur le développement des ravins du bassin versant d'Oued Maiez en Tunisie Centrale

L'érosion ravinante réduit de plus en plus les terres cultivables en Tunisie Centrale en les transformant en badland. Le développement des ravins est variable dans l'espace et dans le temps suite à la variabilité des paramètres physiques et naturels qui régissent l'accroissement des ravins. Nous nous sommes proposés dans cette recherche d'étudier l'effet des formations lithologiques sur le développement des ravins dans le bassin versant de 1500 ha d'Oued Maiez situé en Tunisie Centrale. Les cartes du réseau hydrographique de 1963 et 1989 ont étéétablies à partir des photographies aériennes au 1/12,500 non redressées. La prospection du terrain nous a permis de constater que la nature lithologique des différentes unités géologiques et superficielles identifiées comme relativement homogènes dans le bassin versant est un facteur déterminant dans le développement des ravins. Ainsi, les argiles gypseuses de la formation Chérichéra (Lutétien-Priabonien) présentent un chevelu de ravins dense alors que les sables fins de l'Oligocène inférieur sont incisés par des ravins en forme de gorges étroites dont la profondeur dépasse souvent les 5 m (Fig. 7). Nous avons alors établi un levé cartographique détaillé au 1/12,500 de ces différentes unités qui sont au nombre de 8. La détermination de la densité du ravinement, définie comme étant le rapport de la longueur des ravins dans une unité lithologique sur sa superficie, a été faite par la numérisation des cartes du réseau hydrographique et géologique et l'extraction à l'aide du système d'information géographique (SIG) Arc/info des ravins inclus dans chacune de ces unités (Figs. 9, 10). Il ressort de cette quantification que, dans les unités dont la superficie varie entre 33.96 ha et 416.86 ha, la densité du ravinement varie entre 101 m/ha et 285 m/ha en 1989 (Tableau 2). La plus faible densité se trouve dans la formation Chérichéra datée de l'Oligocène inférieur à moyen et constituée par la superposition de plusieurs séquences élémentaires d'argile feuilletée verte, de silt et de grès roux coquillier à ciment calcaire. La plus forte densité se trouve dans l'unité 2 datée du Lutétien supérieur- Priabonien et composée d'argiles verdatres à violacées riches en gypses lamellaires.     

Highlighting delayed elastic processes at zero stress in a polymer glass

The present study highlights the existence of a post‐evolution of the fracture and damage in glassy polymers at zero‐stress relaxation evidencing that the dynamic is not frozen below the glass transition but that it releases at zero stress in the plastic regime from past stresses. The observation of a further evolution of the glass without applied stress (at zero stress) is unexpected and inaccessible using conventional tensile tests since they are not designed to enable a zero‐stress measurement. Non‐contact methods such as confocal microscopy and autocorrelation analysis are used to examine polymethylmethacrylate samples plastically deformed (up to 8% elongation rate) and subsequently studied in the unloaded state. The zero‐stress evolution is morphologically characterized by a nucleation of new microfractures and an evolution of the existing cracking. The analysis of the image correlation indicates that the strain field continues to evolve revealing an intermittent retraction of the displacement field at time scales up to several days. Different temperatures from ?75 °C up to ?45 °C below the glass transition have been tested and prove that the retraction process is thermally activated. The retraction process (about 1% ? 2% of the deformation rate) implies that plastic deformation does not relax completely from anterior stresses but exhibits a delayed elasticity. These properties have profound consequences impacting the future physical and mechanical properties of the material. © 2015 Society of Chemical Industry     

Layered space-time multiuser detection over wireless uplink systems

In this paper, we investigate the use of layered space-time (also known as the vertical Bell Laboratories layered space-time (V-BLAST) scheme) for multiuser detection in fading channels. The multiple transmit antennas in V-BLAST are treated as individual mobile station transmitters, while the base station consists of multiple receive antennas. In the proposed system, users are organized in groups and allocated a unique spreading code within the same group. Using these codes, we are able to separate the different groups, and layered space-time algorithm is then invoked to further remove the remaining interference between users. A decorrelator-type receiver-based layered space-time detection is proposed for both complex and real constellations. For the latter case, we derive our receiver after evaluating and comparing the performance of two decorrelators based on the V-BLAST scheme. It is demonstrated that a significant performance improvement and increase in system capacity is obtained with very low spreading factors. Further results are also introduced by considering reduced complexity receivers based on serial layered space-time group multiuser detection, and parallel layered space-time group multiuser detection.     

Experimental study of convective heat transfer on a finned rotating cylinder

In this study, the local convective heat transfer from a rotating finned cylinder to the surrounding air was evaluated using an infrared thermographic experimental set up. Solving the inverse conduction heat transfer problem allows the local convective heat transfer coefficient to be identified. We used the specification function method, along with spatio-temporal regularization, to develop a model of local convective heat transfer in order to take lateral conduction and 2D geometry into account. This model was tested using rotational Reynolds numbers (based on the cylinder diameter and the peripheral speed) between 4300 and 17 900. The local heat transfer on the fin surface was analyzed to determine the influence of the rotational Reynolds number and the influence of the height and spacing of the fins. In this paper, we propose an efficiency definition that allows the optimal geometrical configuration of the finned cylinder to be identified for the given operating conditions.     

Structural, morphological and mechanical characteristics of polyethylene, poly(lactic acid) and poly(ethylene-co-glycidyl methacrylate) blends

In this work, uncompatibilized and compatibilized blends of low density polyethylene (LDPE) and poly(lactic acid) (PLA) were subjected to several investigations: Fourier transform infrared (FTIR) spectroscopy, morphological analysis and mechanical testing (tensile, impact, microhardness). The copolymer (ethylene-co-glycidyl methacrylate) (EGMA) was used as compatibilizer. The percentages of PLA in LDPE/PLA samples ranged from 0 to 100 wt% while the EGMA was added to the blend 60/40 (LDPE/PLA) at concentrations of 2, 5, 7, 10, 15 and 20 parts per hundred (phr). FTIR analysis showed the absence of any interaction between LDPE and PLA, but after addition of compatibilizer, reactions between epoxy groups of EGMA and carboxylic or hydroxyl groups of PLA were confirmed. Tensile and impact tests revealed a loss of ductility of LDPE with the incorporation of PLA, except for the composition 80/20 (LDPE/PLA). However, the addition of 15 phr of EGMA led to the maximum increase in the elongation-at-break (about three times the value of uncompatibilized blend) and in the impact strength, but a marginal improvement was observed for tensile strength. SEM micrographs confirmed that the enhancement of mechanical properties is due to the improvement of the interfacial adhesion between different phases owing to the presence of EGMA. The microhardness values of the different blends (uncompatibilized or compatibilized) were in good agreement with the macroscopic mechanical properties (tensile and impact strengths).     

Impact of cleaning and disinfection on the non-culturable and culturable bacterial loads of food-contact surfaces at a beef processing plant

We assessed the impact of industrial cleaning and disinfection (C&D) on colony-forming units (CFUs), viable (culturable and viable but non-culturable) cells and on total cells (viable and dead cells). Bacterial loads on polyvinyl chloride (PVC) and stainless steel surfaces in a cutting room at a beef processing plant were determined before and after C&D by real-time PCR to quantify cells from successive swabs from surfaces with or without an ethidium monoazide pre-treatment and by CFU counts on tryptone soy agar. Agar contact plates were also applied after C&D for comparison. Before C&D, total cells reached 5.4 and 4.7logcells/cm(2), viable cells 4.0 and 4.4logcells/cm(2) and CFUs 3.1 and 2.9logCFU/cm(2) on PVC and stainless steel surfaces, respectively. Although C&D left surfaces visually clean, it did not lead to a significant reduction in total cells. Significant reductions were only observed on PVC for CFUs: 0.8 log and on stainless steel surfaces for viable cells and CFUs: 0.8 and 1.5 log, respectively. Our results show that CFUs were both more easily detached and killed on stainless steel surfaces than on PVC surfaces. Other important results include the following observations: 1) a single swabbing detached only between 2 and 27% of the actual bacterial load; 2) after C&D, the difference between the actual culturable population and the one assessed by one agar contact plate was 1.9 and 2.7logCFU/cm(2) on PVC and stainless steel surfaces, respectively.     

Genetic algorithms and particle swarm optimization for exploratory projection pursuit

Exploratory Projection Pursuit (EPP) methods have been developed thirty years ago in the context of exploratory analysis of large data sets. These methods consist in looking for low-dimensional projections that reveal some interesting structure existing in the data set but not visible in high dimension. Each projection is associated with a real valued index which optima correspond to valuable projections. Several EPP indices have been proposed in the statistics literature but the main problem lies in their optimization. In the present paper, we propose to apply Genetic Algorithms (GA) and recent Particle Swarm Optimization (PSO) algorithm to the optimization of several projection pursuit indices. We explain how the EPP methods can be implemented in order to become an efficient and powerful tool for the statistician. We illustrate our proposal on several simulated and real data sets.     

Reduction electrochimique de composes organiques en presence de tensio-actifs—I. etude polarographique de nitrobenzenes monosubstitues en milieu acide

During the polarographical reduction of substituted nitrobenzenes in acidic medium, the potential value of the four-electron reduction wave is shifted towards more negative values when BRIJ or CTAB are added.The E_{$\text{1}\text{2}$} variations, according to the surfactant concentration, indicate the formation stage of micelles. This one is only slightly modified by the nature of the substituents, used: CN, Cl, F, CH₃, OCH₃, NH₂.The differences between the E_{$\text{1}\text{2}$} values in aqueous and micellar mediums are always more important with BRIJ than CTAB, but they are similar, for the two surfactants, according to the various substituents.Plotting the E_{$\text{1}\text{2}$} and δ substituents values (according to Hammett and Taft parameters) indicates a linear variation with the same correlation coefficient with CTAB 10^?2 M, BRIJ 10^?2 M or without surfactant. The slopes are therefore quite different and measure: 0.15, 0.20, 0.24 V.The reaction kinetics are almost unmodified by CTAB additions, but strongly slowed by BRIJ additions.