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Natural Convection in a Horizontal Cylinder with Partial Heating: Energy Efficiency Analysis

Journal of Thermal Science 2020年第6期29卷 1531-1550页

作者： MAZGAR Akram JARRAY Khouloud HAJJI Fadhila ben nejma faycal The Higher Institute of Applied Sciences and Technology of Sousse University of SousseTunisia-Ibn Khaldun StreetTaffala City4003 SousseTunisia The Preparatory Institute for Engineering Studies of Monastir University of MonastirTunisia-Rue Ibn El Jazzar5019 MonastirTunisia

The current study reports a numerical analysis of free convection of air in an isothermal horizontal cylinder,cooled and heated at different wall *** heater sizes are discussed in this *** first heated zone is spread across one-quarter of the sidewall;the second is uniformly distributed over the half of the wall and the third active wall covers three-quarters of the *** various locations are considered and examined for each active zone of the *** computation is carried out for Rayleigh number ranging from 102 to *** results characterizing heat transfer and flow features are achieved using an iterative model developed in COMSOL *** effect of Rayleigh number on heat transfer and fluid flow characteristics within the cavity are *** attention is paid to the influence of heater location and heater size on energy *** is found that the mean Nusselt number and dimensionless velocity increase when increasing the Rayleigh ***,the optimal level of energy efficiency is achieved if the heating zone is centered at the upper part of the cylinder,regardless of the heater *** is also shown that the optimal configuration providing higher energy efficiency is obtained when three-quarters of the sidewall are locally heated,and more precisely,if the active zone is centered at the top of the cylinder.

关键词： natural convection cylinder partial heating energy efficiency Rayleigh number

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Densification and Microstructure of Fluorapatite Sintered with Alkaline and Alkaline-Earth Additives

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Journal of Materials Science and Chemical Engineering 2018年第1期6卷 52-67页

作者： Mustapha Hidouri faycal ben Tahar Khaled Bouzouita Higher Institute of Applied Sciences Gabes University Gabes Tunisia RU Catalysis and Materials for Environment and Process Engineering School Gabes University Gabes Tunisia

A study was performed to investigate the effect of some selected sintering additives on the densification and microstructure of fluorapatite (FAp, Ca10(PO4)6F2). The sintering aids, used for improving the material densification at lower than 1080℃ temperature, were classified according to their cations as alkaline such as Li2CO3, NaF, Na2CO3, Na3PO4, KCl, K2CO3, and alkaline-earth such as CaF2, CaCl2 and MgCl2. Amounts of 0.1;1 and 3 wt% were vigorously homogenized with FAp powders then the solid mixture was pressurelessly sintered under argon flow with 10℃ .?min-1 heating and cooling speed. The density of each sintered material was determined by calculation of the pellet dimension and weight, the crystalline phases were identified using X-ray diffraction (XRD) and the phase morphology was examined by scanning electron microscopy (SEM). The dependence of densification and microstructure on sintering temperature range 900℃ - 1000℃ and amount of sintering aids was studied. It was found that all sintering additives were able to ameliorate the sintrability of the material at temperatures 900℃ and 1000℃. Maximums of about 96% were reached with adequate amounts and sintering temperatures. An exception was found with KCl which had no effect on the density. The microstructures of sintered specimens strictly follow the densification ratios and the sintering mechanism depended on the melting point of the additive.

关键词： Fluorapatite Sintering Additive Densification Microstructure

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Glucose Metabolism Disorders in Cirrhosis: Frequency and Risk Factors in Tunisian Population. Results of a Cross-Sectional Study

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Open Journal of Gastroenterology 2014年第8期4卷 289-294页

作者： Rym Ennaifer Myriam Cheikh Rania Hefaiedh Hayfa Romdhane Houda ben nejma Najet Bel Hadj Department of Hepato-Gastro-Enterology Mongi Slim Universitary Hospital Tunis Tunisia

Background and aims: Alterations in carbohydrate metabolism are frequently observed in cirrhosis;to determine the frequency of diabetes mellitus and impaired glucose tolerance in Tunisian cirrhotic patients and identify risk factors. Patients and methods: Cross-sectional study;fasting plasma glucose levels were measured in consecutive patients with cirrhosis. Oral glucose tolerance test was performed if fasting plasma glucose level was normal. Glucose metabolism disorders were then classified as: impaired glucose tolerance and diabetes mellitus. Cirrhotics with glucose metabolism disorder were compared to those without. Results: Seventy-seven patients with cirrhosis were included: 68.8% were diagnosed as having glucose metabolism disorder;diabetes in 42.8% and impaired glucose tolerance in 26%. The tests were able to identify 60.4% of glucose metabolism disorders. Univariate analysis disclosed a higher proportion of female gender (p = 0.04) and more frequent familial history of diabetes mellitus (p = 0.005) in the group with glucose metabolism disorder. There were no statistically differences regarding age, etiology and severity of the cirrhosis, and dry body mass index. Multivariate analysis showed that familial history of diabetes was the only independent risk factor (OR = 5.1, p = 0.005). Conclusion: In our study, the frequency of glucose metabolism disorders was 68.8%. Oral glucose tolerance test allowed disclosing nearly half of them, pointing a high incidence of latent glucose metabolism disorders. In this way, it should be routinely evaluated in all patients with cirrhosis. Familial history of diabetes was the only independent risk factor, suggesting that other factors in addition to liver disease may play a role.

关键词： Cirrhosis Diabetes Impaired Glucose Tolerance

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