D. Andrew S. Rees

Determination of the molecular diffusion coefficients in ternary mixtures by the sliding symmetric tubes technique

A new analytical methodology has been developed to determine the diagonal and cross-diagonal molecular diffusion coefficients in ternary mixtures by the Sliding Symmetric Tubes technique. The analytical solution is tested in binary mixtures obtaining good agreement with the results of the literature. Results are presented for the ternary mixture formed by tetralin, isobutylbenzene, and dodecane with an equal mass fraction for all the components (1-1-1) which is held at 25 °C. Diagonal and cross-diagonal coefficients are determined for the three possible orders of components, in order to compare the results with those available in the literature. A comparison with published results shows a good agreement for the eigenvalues of the diffusion matrix, and a reasonable agreement for the diagonal molecular diffusion coefficients.

Contribution to the benchmark for ternary mixtures: Determination of Soret coefficients by the thermogravitational and the sliding symmetric tubes techniques

This work is part of an international project for the research on the transport properties in ternary mixtures. Six different teams have analysed the same mixture by independent techniques in order to compare the results and validate the techniques. This work is the contribution of the team of Mondragon Unibertsitatea for ground conditions measurements. This team has measured the thermodiffusion coefficients by the thermogravitational techniques and the molecular diffusion coefficients by the Sliding Symmetric Tubes technique. The Soret coefficients have been determined by the combination of the thermodiffusion and molecular diffusion coefficients. The mixture chosen for the study is the one formed by 1,2,3,4-tetrahydronaphtalene, isobutylbenzene and n-dodecane at mass fraction of 80% of THN, 10% of IBB and 10% of n C12, and at 25°C. The good agreement between the results of the different teams shows the validity of the techniques used in this work.Graphical abstract

Forced convection past a heated cylinder in a porous medium using a thermal nonequilibrium model: boundary layer analysis

Abstract We study the forced convective heat transfer from a uniform temperature cylinder placed perpendicular to an otherwise uniform fluid stream in a porous medium. Attention is focussed on how the absence of local thermal equilibrium between the solid and fluid phases affects the rate of heat transfer from the cylinder when the Peclet number is very large. It is found in all cases that the surface rate of heat transfer for the fluid is always greater than that of the solid matrix. Detailed numerical results are given for a wide range of parameter values, and these are supplemented by asymptotic analyses for both small and large values of the inter-phase heat transfer coefficient, H. When this coefficient is small the thermal field corresponding to the solid phase occupies a much greater region than does the thermal field of the fluid phase.

Linear Instability of a Horizontal Thermal Boundary Layer Formed by Vertical Throughflow in a Porous Medium: The Effect of Local Thermal Nonequilibrium

In this paper we investigate the onset of convection in a saturated porous medium where uniform suction into a horizontal and uniformly hot bounding surface induces a stationary thermal boundary layer. Particular attention is paid to how the well-known linear stability characteristics of this boundary layer are modified by the presence of local thermal nonequilibrium effects. The basic conduction state is determined and it is found that the boundary layer forms two distinct regions when the porosity is small or when the conductivity of the fluid is small compared with that of the solid. A linearised stability analysis is performed which results in an ordinary differential eigenvalue problem for the critical Darcy–Rayleigh number as a function of the wave number and the two nondimensional parameters,

Vortex instability from a near-vertical heated surface in a porous medium II. Nonlinear evolution

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Linear stability of a developing thermal front induced by a constant heat flux

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Linear and nonlinear convection in porous media between coaxial cylinders

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