1,721,008 research outputs found
Analisi sperimentale dell’efficienza di pressurizzazione differenziale tra ambienti confinanti per il controllo del trasporto aeraulico di contaminante in degenze ospedaliere
No full textExperimental analysis of the heat transfer coefficient enhancement for a heated cylinder in cross-flow downstream a grid flow perturbation
No full textPenetrative convection of water in cavities cooled from below
No full textTransient natural convection in water-filled square enclosures with the bottom wall cooled at 0 °C, and the top wall heated at a temperature spanning from 8 to 80 °C, is studied numerically for different widths of the cavity in the hypothesis of temperature-dependent physical properties, starting from the initial condition of motionless fluid at the uniform temperature of the top wall. The sidewalls are assumed to be adiabatic. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. The propagation of convective motion from the bottom toward the top of the enclosure is investigated up to the achievement of a steady-state or a periodically-oscillating asymptotic solution. It is found that the ratio between the penetration depth and the cavity size increases as the temperature of the heated top wall decreases and the cavity size increases. Moreover, when the configuration is such that the buoyancy force in the water layer confined between the cooled bottom wall and the density-inversion isotherm is of the order of that required for the onset of convection, the asymptotic solution is periodical. Finally, the coefficient of convection decreases with increasing both the cavity width and the imposed temperature difference. Dimensionless correlations are developed for the calculation of the heat transfer rate across the enclosure and the penetration depth
Experimental analysis of the transport of airborne contaminants between adjacent rooms at different temperature due to the door opening
No full textHeat Loss from Buried Vertical Plate with Assigned Temperature Distribution
No full textThermal losses for a buried vertical thin plate can be expressed as a function of the assigned temperature distribution, the medium conductivity and the geometrical properties that describe the model. When the geometrical properties reduce to one, the plate-ground thermal resistance can be expressed regardless of plate dimension, depending only on temperature distribution given at surface plate and its temperature difference with medium
Interaction between the ion beam produced by an electric thruster and the surface of the host spacecraft.
No full textCombined Effects of Slip Motion and Boundary Conditions on Enhanced Heat Transfer in Natural Convection Flows of Enclosed Nanofluids
No full textThe experimental studies dealing with natural convection of nanofluids in differentially heated enclosures demonstrate that the addition of nanoparticles to a pure base liquid is substantially detrimental, which can be ascribed to the formation of two stagnant fluid layers near the top and bottom adiabatic walls. Thus, if the horizontal walls are differentially heated instead of being perfectly insulated, the consequent development of a pair of concentration boundary layers near them may possibly imply a heat transfer enhancement. In this connection, a two-phase mixture model is employed to perform a numerical study of laminar natural convection in a square cavity containing water suspensions of alumina nanoparticles with a diameter of 33 nm and an average volume fraction in the range 0.001–0.04, assuming that Brownian diffusion and thermophoresis are the primary slip mechanisms between solid and liquid phases. The cavity is differentially heated at sides, whereas the horizontal walls are assumed to be either adiabatic or one heated and the other cooled, with a Rayleigh number in the range 4 × 105–3 × 106. It is found that the heating-from-below configuration is featured by periodic heat transfer, with a rate remarkably higher than that typical of the pure base liquid
Natural convection in square enclosures differentially heated at sides using alumina-water nanofluids with temperature-dependent physical properties
Full text linkLaminar natural convection of Al2O3 + H2O nanofluids inside square cavities differentially heated at sides is studied numerically. A computational code based on the SIMPLE-C algorithm is used for the solution of the system of the mass, momentum and energy transfer governing equations. Assuming that the nanofluid behaves like a single-phase fluid, these equations are the same as those valid for a pure fluid, provided that the thermophysical properties appearing in them are the nanofluid effective properties. The thermal conductivity and dynamic viscosity of the nanofluid are calculated by means of a couple of empirical equations based on a wide variety of experimental data reported in the literature. The other effective properties are evaluated by the conventional mixing theory. Simulations are performed for different values of the nanoparticle volume fraction in the range 0-0.06, the diameter of the suspended nanoparticles in the range 25-100 nm, the temperature of the cooled sidewall in the range 293-313 K, the temperature of the heated sidewall in the range 298-343 K, and the Rayleigh number of the base fluid in the range 103-107. All computations are executed in the hypothesis of temperature-dependent effective properties. The main result obtained is the existence of an optimal particle loading for maximum heat transfer, that is found to increase as the size of the suspended nanoparticles is decreased, and the nanofluid average temperature is increased
A two-phase numerical study of buoyancy-driven convection of alumina-water nanofluids in differentially-heated horizontal annuli
No full textHeat transfer of nanofluids in turbulent pipe flow
No full textHeat transfer of nanoparticle suspensions in turbulent pipe flow is studied theoretically. The main idea upon which this work is based is that nanofluids behave more like single-phase fluids than like conventional solid liquid mixtures. 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 regard, two empirical equations, based on a wide variety of experimental data reported in the literature, are used 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 novelty of the present study is that the merits of nanofluids with respect to the corresponding base liquid are evaluated in terms of global energetic performance, and not simply by the common point of view of the heat transfer enhancement. Both cases of constant pumping power and constant heat transfer rate are investigated for different operating conditions, nanoparticle diameters, and solid liquid combinations. The fundamental result obtained is the existence of an optimal particle loading for either maximum heat transfer at constant driving power or minimum cost of operation at constant heat transfer rate. In particular, for any assigned combination of solid and liquid phases, it is found that the optimal concentration of suspended nanoparticles increases as the nanofluid bulk temperature is increased, the Reynolds number of the base fluid is increased, and the length-to-diameter ratio of the pipe is decreased, while it is practically independent of the nanoparticle diameter. (C) 2012 Elsevier Masson SAS. All rights reserved
- …
