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  • An Implicit Unsteady Finite Volume Formulation for Natural Convection in a Square Cavity
  • Abstract This article describes an implicit method for the solution of time dependent Navier-Stokes equations written in terms of vorticity and velocity. The field equations are discretized using a finite volume technique over quadrilateral meshes.
    The numerical code has been applied to the classical window cavity test, employing a fine stretched non-uniform grid, in order to provide an accurate steady solution for a high value of the Rayleigh number (108). It has also been performed a simulation for a value of Rayleigh larger than the critical value, in order to show the capabilities of the proposed method to properly simulate…
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  • Numerical Study of Convective Heat Transfer in a Horizontal Channel
  • Abstract This study is devoted to the investigation of natural convection in a two dimensional horizontal channel with rectangular heated blocks at the bottom. The aspect ratio of the channel is A = L'/H' = 5. The blocks are heated with a constant temperature while the upper plane of the channel is cold. The governing equations are solved using a finite volumes method and the SIMPLEC algorithm is used for the treatment of the pressure-velocity coupling. Special emphasis is given to detail the effect of the Rayleigh number and blocks height on the heat transfer and the mass flow rate generated…
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  • Electromagnetic Levitation Part III: Thermophysical Property Measurements in Microgravity
  • Abstract Strong inhomogeneous magnetic fields are necessary to generate a finite levitation force in ground based electromagnetic levitation techniques. External forces such as magnetic and gravitational forces influence the oscillation spectrum and counteract the surface movement resulting in a frequency shift, and making the use of electromagnetic levitation techniques in microgravity an attractive alternative to measure thermophysical properties of liquid metals. Under microgravity conditions the magnetic field strength around a liquid droplet is significantly lower than that required to position the same specimen against earth gravity. Hence, a low magnetic field strength results in a low amount of heat energy absorbed…
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  • Towards a Numerical Benchmark for 3D Low Mach Number Mixed Flows in a Rectangular Channel Heated from Below
  • Abstract In the literature, only few references have dealt with mixed-convection flows in the low Mach number approximation. For this reason, in the present study we propose to extend the standard 3D benchmark for mixed convection in a rectangular channel heated from below (Medale and Nicolas, 2005) to the case of large temperature variations (for which the Boussinesq approximation is no longer valid). The Navier-Stokes equations, obtained under the assumption of a low Mach number flow, are solved using a finite volume method. The results, corresponding to the steady-state case of the benchmark, lead to the idea of launching a call…
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  • Mixed Convection in Horizontal Internally Finned Semicircular Ducts
  • Abstract The problem of combined free and forced convection in horizontal semicircular ducts (flat wall at the bottom) with radial internal fins is investigated from a numerical point of view. The wall of the duct is assumed to have a uniform heat input along the axial direction with a uniform peripheral wall temperature (H1). The analysis focuses on the case of hydrodynamically and thermally fully-developed laminar flow. The governing equations for the velocity and temperature are solved by using a control-volume-based finite-difference approach. The fluid flow and heat transfer characteristics are found to be dependent on the Grashof number, the fin…
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  • Detailed Observations of Convective Instability on an Interfacial Salty Layer
  • Abstract This paper focuses on the mechanisms of convective instability in a stable salty gradient layer (i.e. an interfacial salty layer). This layer is assumed to be initially confined between two homogeneous liquid layers: a lower layer composed of salty water of 5wt% concentration and an upper layer composed of distilled water. The mechanisms underlying the interfacial salty layer's instability are depicted experimentally using a PIV technique and via measurements of concentration and temperature. It is found that in addition to the effect of double-diffusion across the interfacial salty layer, different forms of Kelvin-Helmholtz instability occur at different locations:\newline i. At…
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  • Analytical Solution of the Thermal Behavior of a Circulating Porous Heat Exchanger
  • Abstract The transient thermal behavior of a two-dimensional circulating porous bed is analytically investigated. A one-energy equation model, representing both the gas and solid phases via a unified temperature, is employed to describe the thermal behavior of the circulating bed. The latter is essentially a tube and shell heat exchanger commonly used in technologically important applications. The model equation is transformed into a simpler set of partial differential equations using an analytical procedure. The analytical solution, based on the method of separation of variables and the principle of superposition, is formulated for the calculation of the temperature distribution in the radial…
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  • Production of Carbon Nanotubes on Different Monel Substrates
  • Abstract Multi-walled carbon nanotubes (MWCNTs) have been produced by chemical vapor deposition using acetylene as a hydrocarbon source at 700 \textdegree C. The Monel substrates coated with MWCNTs can be used later as cathodes in the Physical Vapor Deposition (PVD) systems to produce CNTs embedded in diamond-like carbon (DLC) film. This new method of generating MWCNTs on Monel substrates without using any catalyst is very simple and uses very little power compared to other CNTs generating techniques. Embedded CNTs in a crystalline carbon coat was observed on mirror-like polished Monel substrates at 700 \textdegree C but not on the rough Monel…
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  • Study of Heat and Mass Transfer in Porous Media: Application to Packed-Bed Drying
  • Abstract This work focuses on tyipical heat and mass transfer phenomena during the processing of products in the context of the packed-bed drying method (products arranged in thick layers into dryers working in forced convection mode). The dryers are modeled as porous media at the macroscopic level. The simulations are carried out using the mass, momentum (written in the framework of the Darcy's law approximation) and energy equations applied for the different components. A diffusion model based on Fick's law is also used to take into account the drying kinetics. This approach allows monitoring of the variations of humidity and temperature…
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