1,723,733 research outputs found
Natural convection in rectangular enclosures heated from below and symmetrically cooled from the top and both sides
No full textHeat transfer features of buoyancy-driven nanofluids inside rectangular enclosures differentially heated at the sidewalls
No full textThe heat transfer features of buoyancy-driven nanofluids inside rectangular enclosures differentially heated at the vertical walls, are investigated theoretically. The main idea upon which the present work is based is that nanofluids behave more like a single-phase fluid rather than a conventional solid liquid mixture, which implies that all the convective heat transfer correlations available for single-phase flows can be extended to nanoparticle suspensions, provided that the thermophysical properties appearing in them are the nanofluid effective properties calculated at the reference temperature. In this connection, two empirical equations, based on a wide variety of experimental data reported in the literature, are developed for the evaluation of the nanofluid effective thermal conductivity and dynamic viscosity, whereas the other effective properties are evaluated by the conventional mixing theory. The heat transfer enhancement across the differentially heated enclosure that derives from the dispersion of nano-sized solid particles into a host liquid is calculated for different operating conditions, nanoparticle diameters, combinations of suspended nanoparticles and base liquid, and cavity aspect ratios. The fundamental result obtained is the existence of an optimal particle loading for maximum heat transfer. Specifically, for any assigned combination of solid and liquid phases, the optimal volume fraction is found to increase slightly with decreasing the nanoparticle size, and to increase much more remarkably with increasing both the nanofluid average temperature and the slenderness of the enclosure. (C) 2010 Elsevier Masson SAS. All rights reserved
Empirical correlating equations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids
No full textIn this paper, two empirical correlations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids, based on a high number of experimental data available in the literature, are proposed and discussed. It is found that, given the nanoparticle material and the base fluid, the ratio between the thermal conductivities of the nanofluid and the pure base liquid increases as the nanoparticle volume fraction and the temperature are increased, and the nanoparticle diameter is decreased. Additionally, also the ratio between the dynamic viscosities of the nanofluid and the pure base liquid increases as the nanoparticle volume fraction is increased, and the nanoparticle diameter is decreased, being practically independent of temperature. The ease of application of the equations proposed, and their wide regions of validity (the ranges of the nanoparticle diameter, volume fraction and temperature are 10-150 nm, 0.002-0.09 and 294-324 K for the thermal conductivity data, and 25-200 nm, 0.0001-0.071 and 293-323 K for the dynamic viscosity data), make such equations useful by the engineering point of view, for both numerical simulation purposes and thermal design tasks. (C) 2010 Elsevier Ltd. All rights reserved
Optimal formulation of nanofluids for maximum free convection heat transfer from horizontal isothermal cylinders
Full text linkFree convection heat transfer in nanofluids from horizontal isothermal cylinders is investigated theoretically. The main idea upon which the present work is based is that nanofluids behave more like a single-phase fluid rather than like a conventional solid-liquid mixture. This assumption implies that all the convective heat transfer correlations available in the literature for single-phase flows can be extended to nanoparticle suspensions, provided that the thermophysical properties appearing in them are the nanofluid effective properties calculated at the reference temperature. In this connection, two empirical equations, based on a wide variety of experimental data reported in the literature, are proposed for the evaluation of the nanofluid effective thermal conductivity and dynamic viscosity. Conversely, the other effective properties are computed by the traditional mixing theory. The heat transfer enhancement that derives from the dispersion of nano-sized solid particles into the base liquid is calculated for different operating conditions, nanoparticle diameters, and combinations of solid and liquid phases. The fundamental result obtained is the existence of an optimal particle loading for maximum heat transfer. In particular, for any assigned combination of suspended nanoparticles and base liquid, it is found that the optimal volume fraction increases as the nanofluid average temperature increases, the nanoparticle size decreases, and the Rayleigh number of the base fluid decreases
El cuento breve.
No full textLidia Corcione Crescini,escritora ,abogada egresada de la Universidad de Cartagena,colaboradora con varias revistas a nivel internacional y columnista del Universal en Cartagena de Indias .En esta ocación nos regala uno de sus escritos llamado :El cuento breve.Donde narra la vida de un campesino agricultor,sus vivencias ,alegrías ,tristezas y quehaceres de su vida cotidiana de una forma tan detallada y descriptiva que logra introducir al lector en su mundo literario
Optimal design of Outdoor Lighting Systems by Genetic Algorithms
No full textThe use of genetic algorithms for the optimal design of lighting systems is illustrated and discussed. The lighting of an outdoor tennis court and of a football field are considered as case-studies. The main aims of the paper are: 1) the evaluation of the performance of the genetic algorithm strategies in comparison with more traditional optimization procedures e.g., Montecarlo and gradient methods, through the study of a relatively simple lighting installation, an outdoor tennis court, whose optimal design solution is calculated in a relatively short time by the analysis of all the possible design alternatives; and 2) the evaluation of the performance of the genetic algorithm strategies applied to the design of a larger and more complex lighting system i.e., that for an outdoor football field, for which a comparison between the results obtained through the optimization procedure and those relevant to an existing lighting installation is examined and discussed. Considerations on both the computational times required and the calculation accuracy obtained are also reported
El cuento breve.
No full textLidia Corcione Crescini,escritora ,abogada egresada de la Universidad de Cartagena,colaboradora con varias revistas a nivel internacional y columnista del Universal en Cartagena de Indias .En esta ocación nos regala uno de sus escritos llamado :El cuento breve.Donde narra la vida de un campesino agricultor,sus vivencias ,alegrías ,tristezas y quehaceres de su vida cotidiana de una forma tan detallada y descriptiva que logra introducir al lector en su mundo literario
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