Thermo-hydrodynamic Airflow Behavior Analysis in Solar Chimney Device

A numerical methodology has been developed to analyze the thermo-hydrodynamic aspect of airflow occurring in solar chimney power plants (SCPP) according to some dominant parameters. The general curvilinear coordinates finite volume method (GCCFVM), which is necessary in the case of turbulent flow through complex geometries, is used in this work. The governing equations describing the steady state turbulent fluid flow are solved numerically using this technique. It is shown that the chimney tower dimensions control directly the hydrodynamic field. However, the collector dimensions control directly the thermal field and indirectly the hydrodynamic field. It is demonstrated that the solar radiation influences strongly and positively the thermo-hydrodynamic field by increasing the mass flow rate. The mass flow decreases with the increase of the ambient temperature and then the system is more efficient with low ambient temperature. Indeed, the mass flow rate increases from 0.8 kg/s up to approximately 2 kg/s when the solar radiation varies between 200 W/m2 and 1000 W/m2 for fixed ambient temperature value of 30 °C. When ambient temperature increases from 10 °C up to 50 °C, the mass flow rate decreases slightly and in a linear manner from 1.7 kg/s to 1.5 kg/s for fixed solar radiation intensity value of 600 W/m2. Contrasting to other studies, conclusion based on simplified analytical models, ambient temperature affects adversely the performance of a SCPP in decreasing the mass flow rate. This conclusion should be taken into consideration when analyzing models dedicated to the prediction of solar chimney power plant performance

The Bou Dahar Jurassic carbonate-hosted Pb–Zn–Ba deposits (Oriental High Atlas, Morocco): Fluid-inclusion and C–O–S–Pb isotope studies

The Bou Dahar Pb–Zn–Ba (±Sr) is hosted in the Lower and Middle Liassic carbonate platform in the oriental High Atlas of Morocco. The paragenetic sequence includes quartz–pyrite–melnicovite–sphalerite–galena– calcite–barite ± fluorite– ± celestite. Fluid-inclusion studies were conducted on sphalerite (early mineralizing stage) and barite, and celestite (late mineralizing stage). These studies reveal two end-member fluids, a hot (~143 °C) and saline fluid (~23 wt.% NaCl eq.) and a cooler (b50 °C) and diluted fluid (~5 wt.% NaCl eq.). Based on fluid-inclusion and C–O–S isotope studies, a conclusion is reached that the Bou Dahar ore deposits were formed by the mixing of two fluid — a diluted, SO2−4-rich fluid, and an 18O-enriched basinal brine that carried Pb, Zn, and Ba. The sulfur required for the precipitation of sulfides was generated by the thermochemical sulfate reduction of dissolved sulfate (SO24−) of the Mesozoic seawaters, and delivered to the site of ore deposition. The sulfur of sulfate minerals was derived directly from these dissolved SO24. The Pb isotope compositions are homogenous with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios ranging from 18.124 to 18.183, 15.630 to 15.634, and 38.325 to 38.440 respectively. This Pb isotope composition is indicative of an upper crust and orogene reservoirs as the source of lead and other metals. The emplacement of mineralization occurred during the Eocene– Miocene Alpine orogeny, and tectonic burial and compression were the driving forces behind the circulation of the orogenic-brines. These ore-forming fluids migrated, along thrusting regional E–W and NE–SW deep-seated faults, to the confined carbonate-Liassic reservoir

Etude numérique et expérimentale de la propagation de fumées entre deux locaux

International audienceCette étude est relative à la compréhension et à la description du phénomène de propagation dans une structure confinée et ventilée mécaniquement. Ceci est réalisé en utilisant deux maquettes à échelle réduite au 1/5, d'un dispositif composé de deux compartiments communiquant par une ouverture verticale. Des simulations numériques ont été menées sur deux codes afin de juger leurs performances vis-à-vis de ce problème

Chemical composition, antimicrobial, antioxidant and anticancer activities of essential oil from Ammodaucus leucotrichus Cosson & Durieu (Apiaceae) growing in South Algeria

ABSTRACT. The chemical composition of the essential oil obtained by hydrodistillation from aerial parts of A. leucotrichus Cosson & Durieu (Apiaceae) grown in the south of Algeria (El-Oued) was determined by GC-MS analysis. The oil was found to be rich in perilladehyde 64.66% and D-Limonene 26.99%. The biological activity of A. leucotrichus Cosson & Durieu essential oil has been investigated. The in vitro antimicrobial activity of the essential oil sample was tested on eight strains, one yeast and one fungi. The test showed interesting antimicrobial properties, especially on Salmonella enterica and E. coli, the antioxidant capacity of the oil was measured using the cyclic voltammetry, and the AAT value of A. leucotrichus essential oil was evaluated 47.84 mg α-TE/L. In addition, the antitumor activity showed that the oil of A. leucotrichus was very significant against the HCT116 colon cancer cell line.               KEY WORDS: Ammodaucus leucotrichus, Antioxidant activity, Anticancer activity, Cyclic voltammetry Bull. Chem. Soc. Ethiop. 2019, 33(3), 541-549. DOI: https://dx.doi.org/10.4314/bcse.v33i3.1

Lubricant Rheological Behavior Effect Analysis on the Performance of Finite Porous Self- Lubricating Journal Bearings

In this paper, the hydrodynamic lubrication of finite porous self-lubricating journal bearings is investigated taking into account the rheological lubricant behavior effect. The modified Reynolds equation is derived by considering both the fluid flow in the porous matrix and the lubricant rheological behavior where Darcy’s law and power- law model were used. Governing differential equations were solved numerically using the finite difference method. Static characteristics are obtained by considering three types of lubricants: pseudo-plastic, dilatant and Newtonian fluids. Obtained results showed that the power law index, n, has important effects on the performance of porous and non-porous bearings. An improvement in the fluid bearing characteristics (load capacity, pressure) is observed for dilatant fluids (n>1) while these characteristics decreased for pseudo-plastic fluids (n<1). The permeability of the porous structure has significant effects on the performance of porous journal bearings of finite length, particularly at higher eccentricity ratios. Good agreement is observed between the results obtained in this study and those of literature revue

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10&nbsp;years; 78.2% included were male with a median age of 37&nbsp;years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Heat and Mass Transfer with Condensation in Capillary Porous Bodies

The purpose of this present work is related to wetting process analysis caused by condensation phenomena in capillary porous material by using a numerical simulation. Special emphasis is given to the study of the mechanism involved and the evaluation of classical theoretical models used as a predictive tool. A further discussion will be given for the distribution of the liquid phase for both its pendular and its funicular state and its consequence on diffusion coefficients of the mathematical model used. Beyond the complexity of the interaction effects between vaporisation-condensation processes on the gas-liquid interfaces, the comparison between experimental and numerical simulations permits to identify the specific contribution and the relative part of mass and energy transport parameters. This analysis allows us to understand the contribution of each part of the mathematical model used and to simplify the study

Contribution à l´analyse de la lubrificationthermo-hydrodynamique des paliers fluides poreux

L’évolution technologique des machines impose des vitesses de rotation de plus en plus élevées, qui, dans certaines conditions sévères de fonctionnement, l’énergie dissipée par cisaillement dans le fluide lubrifiant serait importante, induisant ainsi l’élévation de sa température. L’échauffement entraîne ainsi une diminution importante de la portance du mécanisme et les caractéristiques mécaniques des matériaux constituant le revêtement interne des coussinets diminuent. Il est à rappeler que l’utilisation des paliers poreux autolubrifiants dans l’industrie remonte à 1925 et leur utilisation n’a cessé de croître depuis. Ils sont utilisés dans les applications où la contamination est intolérable tel que l’industrie agroalimentaire et l’industrie du textile. Ils sont également utilisés dans les machines outils, les pompes à eau, les machines à laver, etc...Ils fonctionnent silencieusement et sans entretien, leur coût est considérablement moins cher que les paliers similaires et extérieurement lubrifiés. Leur courte durée de vie et les faibles charges supportées sont leurs inconvénients principaux. Le travail présenté est relatif à une étude par voie de simulation numérique d’un problème de lubrification thermo- hydrodynamique d’un palier fluide autolubrifiant de longueur finie. Elle consiste en l’analyse de l’influence des effets thermiques sur le comportement des paliers poreux autolubrifiants. L'équation de Reynolds des films minces visqueux est utilisée en considérant également le mouvement d'huile dans la matrice poreuse. Le débit de fluide dans la structure poreuse est considéré gouverné par la loi de Darcy. Les effets de la perméabilité du milieu poreux et de l’excentricité sur les performances de ces paliers autolubrifiants sont présentés et discutés. Les résultats obtenus dans le cas hydrodynamique sont en bon accord avec ceux issus de la littérature. Les résultats obtenus dans le cas thermo- hydrodynamique ont montré que l'influence de la température sur le rendement des paliers fluides est non négligeable dans divers cas d'exploitation. Par ailleurs, l’augmentation de la perméabilité du milieu induit la réduction progressive de la répartition de pressions, de la capacité de charge et de l'angle de calage

Optimization of Cellular Concrete Formulation with Aluminum Waste and Mineral Additions

The paper aims to study cellular concrete with a new approach of formulation without an autoclave, with the use of aluminum waste and incorporation of mineral additions into the sand and evaluate its physical and mechanical properties. In this experimental study, two types of cellular concrete are prepared, based on crushed and dune sand with the incorporation of 15% of the slag and 10% of pozzolana, as sand replacement. An experimental program was performed to determine the compressive strength at 28 days, the density and thermal conductivity of the confected cellular concrete. The obtained results showed that concretes prepared with crushed sand developed better mechanical resistance compared to the dune sand. It is also noted that the concretes containing the mineral additions provide a substantial increase in compressive strength in particular slag. Furthermore, cellular concretes with sand dunes offer better thermal conductivity, compared to those with crushed sand. The use of the additions reduces the Water/Binder (W/B) ratio and leads to a lower thermal conductivity regardless of the used sand nature. The outcome of the present study here in could present a modest contribution for the production of cellular concrete with local materials in particular dune sand, active mineral addition and aluminum waste. The physical and mechanical properties obtained from this new composition are estimated acceptable compared to those of the industry-prepared cellular concrete product. Doi: 10.28991/cej-2021-03091721 Full Text: PD