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Fellbach, Germany

Avramenko A.A.,Ukrainian Academy of Sciences | Shevchuk I.V.,MBtech Group | Tyrinov A.I.,Ukrainian Academy of Sciences | Blinov D.G.,Ukrainian Academy of Sciences
Applied Thermal Engineering | Year: 2014

Processes of momentum, heat and mass transfer at the condensation of the stationary vapor with nanoparticles near a vertical plate were investigated using an approximate analytical model. This model extends the classical model of Nusselt by way of the inclusion of an equation for the nanoparticle concentration and a dependence of the nanofliud density on the nanoparticles concentration. Thus, mechanisms of the Brownian and thermophoretic diffusion are incorporated. The essential novelty lies in the identification of three main dimensionless parameters, which describe the influence of nanoparticles on heat transfer and fluid flow. They are (i) the parameter A that denotes the relation between the mechanisms of the thermophoretic and Brownian diffusion, (ii) the concentration φ∞ of nanoparticles in the vapor, and (iii) the ratio R of the densities of the nanoparticles and the fluid. Novel analytical solutions were derived that describe velocity profiles, the mass flow rate and the thickness of the film as the functions of the parameters A, φ∞ and R. Finally, a novel analytical solution for the normalized Nusselt number was obtained as a function of the aforementioned three dimensionless parameters. An increase in each of these parameters causes an increase in the normalized Nusselt number. © 2014 Elsevier Ltd. All rights reserved. Source

Avramenko A.A.,Ukrainian Academy of Sciences | Tyrinov A.I.,Ukrainian Academy of Sciences | Shevchuk I.V.,MBtech Group
Physics of Fluids | Year: 2015

The paper presents results of an investigation of the response of an incompressible fluid in a circular micropipe and a parallel-plate microchannel to a sudden time-independent pressure drop. Solutions of the problem were obtained analytically using the Laplace transform technique and numerically using the lattice Boltzmann method. The unsteady velocity profiles in the pipe and in the channel were obtained with the help of the infinite series solutions validated against numerical simulations. In line with the expectations, the flow asymptotically tends to the fully developed pattern, which is attained quicker for smaller Knudsen numbers. The solution enabled also obtaining relations to estimate the hydraulic resistance coefficient. © 2015 AIP Publishing LLC. Source

Harmand S.,University of Lille Nord de France | Harmand S.,University of Valenciennes and HainautCambresis | Pelle J.,University of Lille Nord de France | Pelle J.,University of Valenciennes and HainautCambresis | And 2 more authors.
International Journal of Thermal Sciences | Year: 2013

Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental/theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steady-state (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infra-red cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk, rotor-stator systems without and with impinging single jets, as well as multiple jets. Conclusions to the review outline perspectives of the further extension of the investigations of different kinds of the rotor-stator systems and their applications in engineering practice. © 2012 Elsevier Masson SAS. All rights reserved. Source

Avramenko A.A.,Ukrainian Academy of Sciences | Blinov D.G.,Ukrainian Academy of Sciences | Shevchuk I.V.,MBtech Group | Kuznetsov A.V.,North Carolina State University
Physics of Fluids | Year: 2012

Heat, momentum, and mass transport in turbulent boundary layer nanofluid flow over a flat plate were investigated. Boundary layer equations were reduced to self-similar forms and solved numerically. The Lie group technique, which is based on the symmetry properties of governing equations, was used to derive self-similar forms of these equations. Turbulent viscosity was predicted using the mixing-length model. Also, dependences of physical properties (viscosity, thermal conductivity, and diffusion coefficients) on the nanofluid concentration and temperature were accounted for. Influences of different dimensionless parameters and nanoparticle concentration on the velocity and temperature profiles, as well as on the relative Nusselt number and skin-friction coefficient, were investigated. © 2012 American Institute of Physics. Source

Fasquelle A.,JEUMONT Electrical | Pelle J.,University of Lille Nord de France | Pelle J.,University of Valenciennes and HainautCambresis | Harmand S.,University of Valenciennes and HainautCambresis | Shevchuk I.V.,MBtech Group
Journal of Heat Transfer | Year: 2014

Cooling of electrical machines is nowadays of high interest in order to improve their efficiency. In railway applications, electrical motors can be shrouded in order to avoid particles to be deposited inside. To ensure a satisfactory cooling, pipes are placed inside the rotor and are thus rotating. Improvements in convective heat transfer inside the rotating pipes were numerically investigated. Model was first validated against experimental data and after that several geometry modifications were tested. Influence of the angle of attack of the fluid at the inlet to the pipe was discussed and it was shown that heat transfer can be significantly increased near the pipe inlet. In addition to that changing a circular pipe with an elliptical pipe was investigated in two ways: fixing the same hydraulic diameter or the same equivalent diameter. It was shown that the cooling efficiency can be significantly increased. The best overall heat transfer enhancement of about 45% exhibited elliptic pipes located orthogonal to the rotation radius and having the same cross-section as the reference circular pipes. Results can be used by designers of electrical machines in order to choose the best cooling strategy. Copyright © 2014 by ASME. Source

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