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Heat transfer by natural convection in a porous layer bounded by two coaxial horizontal cylinders.

Transfert de chaleur par convection naturelle dans une couche poreuse limitée par deux cylindres coaxiaux horizontaux.

Author(s) : CALTAGIRONE J. P.

Type of article: Article, IJR article

Summary

Natural convection in a porous medium is studied for the geometrical configuration defined by two concentric horizontal cylinders with isothermal and impermeable surfaces, representing a cylinder or a pipe insulated by a layer of porous material Two methods of investigation are used to approach the phenomenon." experiments on a cell of large aspect ratio (cylinder length to outside diameter), and a numerical model on a two-dimensional plane area. The experimental results reveal three different regimes according to the value of the Rayleigh number. For a finite radial gradient, thermoconvective phenomena develop in the annular layer, but as long as these are not amplified too much, the isotherms remain practically concentric with the cylinders, and heat transfer occurs essentially through conduction. A t higher Rayleigh numbers natural convection develops in the form of two-dimensional counter-rotational vortices which are symmetrical with respect to a vertical plane containing the axis common to both cylinders. The third regime, observed at higher Rayleigh numbers, corresponds to a fluctuating evolution of the temperature field which becomes three-dimensionaL As the inside cylinder is warmer, instabilities occur in the upper part of the model causing some periodicity of the temperature distribution along a generatrix, with a period of about the radius difference. A relative increase in the heat transfer between the cylinders due to the instabilities is observed. A two-dimensional numerical model, using the method of finite differences, enables us to describe the first two regimes observed experimentally, and to define the temperature field and the streamlines for a given Rayleigh number. The total heat transfer calculated is represented by a correlation between the Nusselt and the Rayleigh numbers for many values of the ratio of the radii. The different results are then compared and analysed from a physical point of view.

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Pages: 27-32

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Details

  • Original title: Transfert de chaleur par convection naturelle dans une couche poreuse limitée par deux cylindres coaxiaux horizontaux.
  • Record ID : 30000707
  • Languages: French
  • Source: International Journal of Refrigeration - Revue Internationale du Froid - vol. 1 - n. 1
  • Publication date: 1978

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