Minea A.A.,Technical University Gheorghe Asachi
International Journal of Heat and Mass Transfer | Year: 2014
At this stage of nanofluids development, their thermal conductivity it is not yet known precisely and the judgment of their true potential is difficult. This fact was illustrated by analyzing their heat transfer performance for laminar fully developed forced convection in a tube with two zones: one adiabatic and one with uniform wall heat flux. Forced convective of a nanofluid that consists of water and Al2O3 in horizontal tubes has been studied numerically. Three different models from the literature are used to express the thermal conductivity in terms of particle loading and they led to different qualitative and quantitative results in a classical problem of replacement of a simple fluid (water) by a nanofluid in a given situation. In particular, the heat transfer coefficient of water-based Al2O 3 nanofluids is increased by 3.4-27.8% under fixed Reynolds number compared with that of pure water. Also, the enhancement of heat transfer coefficient is larger than that of the effective thermal conductivity at the same volume concentration. Moreover, the effect of uncertainties in modeling nanofluids properties was noticed. © 2013 Elsevier Ltd. All rights reserved.
Axinte E.,Technical University Gheorghe Asachi
Materials and Design | Year: 2012
Metallic glasses, first discovered a half century ago, are currently among the most studied metallic materials. Available in sizes up to several centimeters, with many novel, applicable properties, metallic glasses have also been the focus of research advancing the understanding of liquids and of glasses in general.Metallic glasses (MGs), called also bulk metallic glasses (BMGs) (or glassy metals, amorphous metals, liquid metals) are considered to be the materials of the future. Due to their high strength, metallic glasses have a number of interesting applications, for example as coatings. Metallic glasses can also be corrosion resistant. Metallic glasses, and the crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Combined with their strength - and now, toughness - this makes them ideal candidates for bio-implants or military applications. Prestigious Journals such as " Nature Materials" , " Nature" frequently publish new findings on these unusual glass materials. Moreover Chinese and Asian scientists have also been showing an interest in the study of metallic glasses.This review paper is far from exhaustive, but tries to cover the areas of interest as it follows: a short history, the local structure of BMGs and the glass forming ability (GFA), BMGs' properties, the manufacturing and some applications of BMGs and finally, about the future of BMGs as valuable materials. © 2011 Elsevier Ltd.
Toma S.L.,Technical University Gheorghe Asachi
Surface and Coatings Technology | Year: 2013
In the arc spraying processes, velocity and temperature of the sprayed particles, which are in a close relationship with the drive jet velocity and temperature, influence the physical and mechanical properties of the coatings. This paper presents a comparative research of 30. T steel deposits, carried out by two spraying procedures: the classic wire arc spraying procedure plus a new one, which represents a combination between the classic wire arc spraying and the flame spraying procedure. The use of a new procedure allowed the increase of the drive jet temperature and the study of its effect created on 30. T deposits properties. The modelling of the arc spraying and the analysis with finite elements in a coupled field allowed the determination of the drive jet temperature variation and the fuel flow, necessary for the temperature to be maintained over 1000. K at spraying distance of 150. mm. The investigations carried out on 30. T steel coatings, obtained by this procedure, demonstrate that the spraying jet temperature increase determines the average growth of the coatings adherence over 18% for cylindrical surface and over 5% for flat surface. Also, these investigations demonstrate the decrease of the average porosity by over 22% for cylindrical surface and by over 17% for flat surface. © 2012 Elsevier B.V..
Axinte E.,Technical University Gheorghe Asachi
Materials and Design | Year: 2011
Glass products have applications in design engineering, and they can solve many special problems. These materials can work in situations in which plastics and metals would fail and need to be part of designer's repertoire. In some situations, by using these materials, some difficult problems would be solved. This paper contains a number of chapters as follows: a brief about ceramics family, a short history of glass, a brief about physics and the technology of glass fabrication, recently developed glasses with special destinations, testing methods and news about glass parts processing (grinding, waterjet processing, laser cutting, nanoimprint lithography, etc.). The last chapter of this review paper contain some strategic lines of glass usage in industry and estimations about the future of glass development. © 2010 Elsevier Ltd.
Plesca A.,Technical University Gheorghe Asachi
Electric Power Systems Research | Year: 2012
This paper describes a simplified thermal model of fast fuse suitable for power electronic circuits, especially for power rectifiers. This model has been validated with a single-phase rectifier and can be used to analyse the thermal behaviour of fast fuses during transient conditions. The procedure for achieving the simplified model is also presented. The parameters' model include all the necessary information about the fast fuse geometry, its components' materials and heat dissipation to the surrounding area. On the basis of this simplified model, the transient thermal behaviour of fast fuse can be estimated for complex power electronic circuit with accuracy and speed. © 2011 Elsevier B.V. All rights reserved.