Heterogeneous nanofluids: natural convection heat transfer enhancement

Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case

Transient behavior inside a vertical cylindrical enclosure heated from the side walls

International audienceA study of the transient laminar free convection in a vertical cylindrical annulus filled with air Pr = 0.71 is conducted numerically and analytically. The governing equations are solved numerically by considering the transient resolutions (direct numerical simulation) in a two-dimensional domain (angular symmetry) using a control-volume numerical approximation. The time evolution is reported in terms of various parameters such as the cylinder curvature and the Rayleigh number. The results reveal that the required time to reach steady state decreases with the convection intensity and is independent of the curvature

Numerical study of melting/solidification by an hybrid lattice method

International audienceIn this paper, we propose a hybrid method coupling a Lattice Boltzmann Method (LBM) and a Finites Volumes Method (FVM), to study melting and solidification problems. The LBM is used to determine the dynamics field while the FVM is applied to discretize the energy equation. This model is validated by comparison to available literature results concerning a square cavity heated without phase change then for the melting of Gallium in an enclosure commonly used as benchmark test case