Romanian Academy Timisoara Branch

Timişoara, Romania

Romanian Academy Timisoara Branch

Timişoara, Romania

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Susan-Resiga R.,Polytechnic University of Timişoara | Muntean S.,Romanian Academy Timisoara Branch | Popescu C.,Polytechnic University of Timişoara
IOP Conference Series: Earth and Environmental Science | Year: 2016

Modern hydraulic turbines require optimized runners within a range of operating points with respect to minimum weighted average draft tube losses and/or flow instabilities. Tractable optimization methodologies must include realistic estimations of the swirling flow exiting the runner and further ingested by the draft tube, prior to runner design. The paper presents a new mathematical model and the associated numerical algorithm for computing the swirling flow at the trailing edge of Francis turbine runner, operated at arbitrary discharge. The general turbomachinery throughflow theory is particularized for an arbitrary hub-to-shroud line in the meridian half-plane and the resulting boundary value problem is solved with the finite element method. The results obtained with the present model are validated against full 3D runner flow computations within a range of discharge value. The mathematical model incorporates the full information for the relative flow direction, as well as the curvatures of the hub-to-shroud line and meridian streamlines, respectively. It is shown that the flow direction can be frozen within a range of operating points in the neighborhood of the best efficiency regime.

Susan-Resiga D.,Romanian Academy Timisoara Branch | Susan-Resiga D.,West University of Timișoara | Vekas L.,Romanian Academy Timisoara Branch | Vekas L.,Polytechnic University of Timişoara
Rheologica Acta | Year: 2014

In this paper, the magnetorheological (MR) and magnetoviscous properties of ferrofluid-based iron particle suspensions were investigated. The 2.1-µm mean size Fe particles were dispersed in high-concentration transformer oil-based ferrofluid, the iron particle volume fraction in the resulting nano-micro composite magnetorheological fluid samples varying from ΦFe = 5 to 40 %. The ferrofluid carrier has φp = 23 % solid volume fraction of magnetic nanoparticles stabilized with chemisorbed oleic acid monolayer and without any excess surfactant. In the absence of the field, the ferrofluid has a quasi-Newtonian behavior with a weak shear thinning tendency. The static yield stress shows an increase of about 3 orders of magnitude for an iron particle content of approx. ΦFe = 25 % (Φtot = 42.25 %), while above this value, a saturation tendency is observed. The dynamic yield stress (Bingham model) also increases with the magnetic induction and the particle volume fraction; however, the saturation of the MR effect is less pronounced. The relative viscosity change has a maximum at ΦFe = (10–15) % due to the accelerated increase of the effective viscosity of the composite for higher Fe content. Addition of micrometer-sized iron particles to a concentrated ferrofluid without any supplementary stabilizing agent proved to be a direct and simple way to control the magnetorheological and magnetoviscous behavior, as well as the saturation magnetization of the resulting nano-micro composite fluid to fulfill the requirements of their use in various MR control and rotating seal devices. © 2014, Springer-Verlag Berlin Heidelberg.

Torac I.,Romanian Academy Timisoara Branch
2014 International Conference on Optimization of Electrical and Electronic Equipment, OPTIM 2014 | Year: 2014

The paper deals with standard three phase low voltage squirrel cage motors in variable speed drives. The aim is to investigate the possibility of improving the machines parameters at low speed. The considered industrial motors are the existing ones, having the rated power between 0.55 kW and 37 kW and 4 and 6 pole. The paper presents also an example emphasizing the possibility of improving the machine parameters using a 'low tool cost' solution. © 2014 IEEE.

Velescu C.,Polytechnic University of Timişoara | Popa N.C.,Romanian Academy Timisoara Branch
The Scientific World Journal | Year: 2014

We analyze the laminar motion of incompressible fluids in self-acting thrust bearings with spiral grooves with inner or external pumping. The purpose of the study is to find some mathematical relations useful to approach the theoretical functionality of these bearings having magnetic controllable fluids as incompressible fluids, in the presence of a controllable magnetic field. This theoretical study approaches the permanent motion regime. To validate the theoretical results, we compare them to some experimental results presented in previous papers. The laminar motion of incompressible fluids in bearings is described by the fundamental equations of fluid dynamics. We developed and particularized these equations by taking into consideration the geometrical and functional characteristics of these hydrodynamic bearings. Through the integration of the differential equation, we determined the pressure and speed distributions in bearings with length in the "pumping" direction. These pressure and speed distributions offer important information, both quantitative (concerning the bearing performances) and qualitative (evidence of the viscous-inertial effects, the fluid compressibility, etc.), for the laminar and permanent motion regime. © 2014 Cornel Velescu and Nicolae Calin Popa.

Greconici M.,Polytechnic University of Timişoara | Koch C.,Polytechnic University of Timişoara | Madescu G.,Romanian Academy Timisoara Branch
EXPRES 2011 - 3rd IEEE International Symposium on Exploitation of Renewable Energy Sources, Proceedings | Year: 2011

The present paper refers to some examples that use the finite element method (FEM) in the process of analysis, design and optimization of the electrical machines used in wind energy conversion systems. The 2D-FEM program Opera 13 of Vector Fields is used in the analyzed examples. These examples refer to two types of synchronous generators with permanent magnets. Some possibilities and advantages of electrical machine optimization, using the FEM-programming packages available today, are pointed out in the present paper. © 2011 IEEE.

Ianos R.,Polytechnic University of Timişoara | Taculescu A.,Polytechnic University of Timişoara | Taculescu A.,Romanian Academy Timisoara Branch | Pacurariu C.,Polytechnic University of Timişoara | Lazau I.,Polytechnic University of Timişoara
Journal of the American Ceramic Society | Year: 2012

Combustion synthesis of Fe 3O 4and properties of the resulted powders have been discussed in relation to reaction atmosphere (in air/in the absence of air) and used fuel (sucrose, citric acid and glucose). Conducting the combustion reactions in air caused the rapid oxidation of Fe 2+ to Fe 3+ under the influence of the atmospheric oxygen; therefore the final reaction product was a mixture of α-Fe 2O 3and γ-Fe 2O 3. In order to avoid the oxidation of Fe 2+ to Fe 3+ a simple but efficient solution has been suggested: combustion reactions were carried out in a round bottom flask and the evolving gases were bubbled in a beaker filled with water. This solution allowed the preparation of Fe 3O 4nanopowders, with crystallite size varying from 10 nm (glucose) to 18 nm (citric acid). Depending on the used fuel, the specific surface area of the magnetite powders varied between 56 m 2/g (citric acid) and 106 m 2/g (glucose). The saturation magnetization of Fe 3O 4powders prepared in the absence of air ranged between 55.3 emu/g (glucose) and 59.4 emu/g (sucrose). © 2012 The American Ceramic Society.

Bernad E.S.,Victor Babes University of Medicine and Pharmacy Timisoara | Bernad S.I.,Romanian Academy Timisoara Branch | Craina M.L.,Victor Babes University of Medicine and Pharmacy Timisoara
Bio-Medical Materials and Engineering | Year: 2014

In this study, effects of serial stenosis on coronary hemodynamics were investigated in the human right coronary artery (RCA) using blood flow analysis. A 3-D model of a serial stenosed RCA was reconstructed based on multislice computerized tomography images. Numerical analysis examined the effect of multiple serial stenoses on the hemodynamic characteristics such as flow separation, pressure drop and FFR. Pressure loss associated with flow expansion after each constriction was large. Overall pressure drop increased from 1700 Pa (12.75 mmHg) at the end diastole to 11000 Pa (82.5 mmHg) at the peak systole. In two stenoses the corresponding pressure gradients werearound 30 mmHg and corresponded to the stenosis with FFR < 0.7 (associated to the sever stenosis). Severe stenosies caused large pressure drops across the throat. Blood flow distal to the stenosis was associated with fluctuations of the wall shear stress and vorticity. © 2014 - IOS Press and the authors. All rights reserved.

Tombacz E.,University of Szeged | Turcu R.,A-D Technologies | Socoliuc V.,Romanian Academy Timisoara Branch | Vekas L.,Romanian Academy Timisoara Branch
Biochemical and Biophysical Research Communications | Year: 2015

Recent developments in nanotechnology and application of magnetic nanoparticles, in particular in magnetic iron oxide nanosystems, offer exciting possibilities for nanomedicine. Facile and precise synthesis procedures, high magnetic response, tunable morphologies and multiple bio-functionalities of single- and multi-core magnetic particles designed for nanomedicine applications are thoroughly appraised. This review focuses on the structural and magnetic characterization of the cores, the synthesis of single- and multicore iron oxide NPs, especially the design of the latter, as well as their protection, stabilization and functionalization by desired coating in order to protect against the corrosion of core, to prevent non-specific protein adsorption and particle aggregation in biological media, and to provide binding sites for targeting and therapeutic agents. © 2015 Elsevier Inc. All rights reserved.

Socoliuc V.,Petru Poni Institute of Macromolecular Chemistry | Socoliuc V.,Romanian Academy Timisoara Branch | Vekas L.,Romanian Academy Timisoara Branch | Turcu R.,A-D Technologies
Soft Matter | Year: 2013

The applicability of aqueous magnetic colloids depends on their colloidal stability under the influence of various factors like external magnetic field and temperature. The magnetically induced phase condensation of magnetic colloids leads to the formation of spindle-like condensed phase drops of highly packed magnetic colloidal particles. The condensed phase drops are aligned parallel to the external magnetic field and may grow up to several microns thickness and tens or even hundreds of microns length. Thus, the magnetically induced phase condensation could be an advantage in magnetic separation applications, whereas in magnetic drug targeting applications it could lead to blood vessel clogging as well as to a significant decrease of the specific surface. We present the results of an experimental study regarding the influence of the external magnetic field and temperature on the magnetically induced phase condensation in an aqueous dispersion of pNIPA magnetic nanogels. A theoretical model was developed for the analysis of the data from forward light scattering experiments. It was found that the volume weight of the condensed phase increases with passing time, with increasing field intensity and temperature decrease. Using the proposed model, the magnetic field intensity dependence of the initial supersaturation of the sample was calculated. © 2013 The Royal Society of Chemistry.

Socoliuc V.,Petru Poni Institute of Macromolecular Chemistry | Socoliuc V.,Romanian Academy Timisoara Branch | Popescu L.B.,Romanian Space Science Institute
Physica A: Statistical Mechanics and its Applications | Year: 2011

In this paper we develop a theoretical model for the magnetically induced optical anisotropy in dense magnetic colloids made of spherical and un-aggregated magnetic monodomain nanoparticles. Both dipolefield and dipoledipole magnetic and electric interactions between the magnetic monodomain particles are taken into account in the Hamiltonian of the system. Using the pair correlation function in a colloidal suspension of magnetic nanoparticles developed by Ivanov and Kuznetsova (2001) [11], the complex dielectric constant of a magnetic colloid is modeled as a function of the light polarization direction, the magnetic field intensity and magnetic particle concentration and diameter. The two main features of the model are that, on the one hand, it predicts the possibility of magnetically induced optical anisotropy in dense magnetic colloids made of spherical and un-aggregated monodomain nanoparticles, and on the other hand, unlike the existing models for diluted samples, it predicts a non-linear dependence of dichroism and birefringence on magnetic particle concentration. © 2010 Elsevier B.V. All rights reserved.

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