Effective thermal conductivity of rough spheres packed beds

ABSTRACT The effective thermal conductivity, k e , rigorously defined on the basis of the local volume averaging method, is an important parameter in porous media. The experimental and numerical results available in literature demonstrate that the k e value is influenced by several parameters such as thermal and mechanical properties of the multiphase porous medium, phase volumetric fractions, geometrical shape and spatial distribution of the solid matrix and, in particular, contact area between the solid particles. In the present paper, a numerical method to evaluate the effective thermal conductivity from the packing structure of a packed bed of mono-sized spheres is validated through the comparison with experimental data, obtained by the authors from an apparatus designed and build up for this purpose. The effects of the spheroid surface roughness is examined as the applied contact load and the solid matrix material vary. In particular packed beds of steel and aluminum spheroids saturated by a static gas (air) have been studied. Unfortunately, the lack of published results including an accurate measurement of the particle roughness does not allow the authors to compare their numerical results with other researchers' experimental data

An innovative method for the thermal conductance measurement of windows

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.One of the most important contributions to the energy requirements in buildings is due to heat transfer through the window surfaces. Therefore, several efforts were made in order to obtain new window frames and glass assemblies with low thermal heat transfer characteristics. To this point of view, it is also necessary to reach accurate measurements of the abovementioned parameters. In this paper, the authors show an innovative measurement method based on radiative and conductive heat transfer which performs window thermal conductance measurements with annexed uncertainty budget evaluation. In the design of the experimental apparatus the authors used a 3D finite volume software whose results were useful for the system optimisation and characterisation.cs201

A macroscale hydrogeological numerical model of the Suio hydrothermal system (Central Italy)

The complex behaviour of the Suio hydrothermal system (central Italy) and its potential exploitation as a renewable energy source are still unclear. To quantitatively evaluate the geothermal resource, the Suio hydrothermal system has been investigated with a hydrogeological numerical model that couples fluid flow, thermal convection, and transport of diluted species inside a hybrid continuum-discrete medium. The numerical model, calibrated and validated with available and new experimental data, unveiled the complex behaviour of the hydrothermal system. The normal tectonic displacements, the fracturing of the karst hydrostructure, and the aquitard distribution strongly influence the hydrothermal basin. In particular, a dual fluid circulation, sustained by steady-state thermal and pressure gradients, modulates the hydrothermalism at the several springs and wells. The presence of a medium to a low-temperature reservoir allows for potential exploitation of the geothermal resource

Electro-Thermal Parameters of Graphene Nano-Platelets Films for De-Icing Applications

This paper provides a study of some relevant electro-thermal properties of commercial films made by pressed graphene nano-platelets (GNPs), in view of their use as heating elements in innovative de-icing systems for aerospace applications. The equivalent electrical resistivity and thermal emissivity were studied, by means of models and experimental characterization. Macroscopic strips with a length on the order of tens of centimeters were analyzed, either made by pure GNPs or by composite mixtures of GNPs and a small percentage of polymeric binders. Analytical models are derived and experimentally validated. The thermal response of these graphene films when acting as a heating element is studied and discussed