Print Email Facebook Twitter Flow and heat transfer measurements in natural convection in coarse-grained porous media Title Flow and heat transfer measurements in natural convection in coarse-grained porous media Author Ataei Dadavi, I. (TU Delft ChemE/Transport Phenomena) Chakkingal, M. (TU Delft ChemE/Transport Phenomena) Kenjeres, S. (TU Delft ChemE/Transport Phenomena) Kleijn, C.R. (TU Delft ChemE/Transport Phenomena) Tummers, M.J. (TU Delft Fluid Mechanics) Date 2019 Abstract This paper reports on an experimental study of natural convection in an enclosure that is heated at the bottom and cooled at the top, filled with a packed bed of relatively large solid spheres. Nusselt numbers were measured for various sphere conductivities, spheres sizes and sphere packings for Rayleigh numbers varying between 107 and 109. The Nusselt number measurements showed that at lower Rayleigh numbers, the heat transfer is lower than that for pure Rayleigh-Bénard convection, with the difference depending on packing type, size, and conductivity of the spheres. However, at high Rayleigh numbers, there exists an asymptotic regime where the convective contribution of the total heat transfer for all sphere conductivities, sizes, and packing types collapse on a single curve which is very close to the curve for pure Rayleigh-Bénard convection. Refractive index-matching of the fluid and the solid spheres enabled the use of particle image velocimetry and liquid crystal thermography to obtain highly resolved velocity and temperature fields. The comparison of the velocity and temperature fields for the two heat transfer regimes showed that the velocity magnitudes inside the pores in the core region are much higher in the asymptotic regime than those in the low Rayleigh number regime, which lead to a deeper penetration of cold and hot fluid elements and higher heat transfer. Subject Heat transferLiquid crystal thermographyNatural convectionParticle image velocimetryPorous media To reference this document use: http://resolver.tudelft.nl/uuid:3d826726-15a9-4cda-9940-3f5c4ee5ddf8 DOI https://doi.org/10.1016/j.ijheatmasstransfer.2018.10.118 Embargo date 2020-11-02 ISSN 0017-9310 Source International Journal of Heat and Mass Transfer, 130, 575-584 Bibliographical note Accepted Author Manuscript Part of collection Institutional Repository Document type journal article Rights © 2019 I. Ataei Dadavi, M. Chakkingal, S. Kenjeres, C.R. Kleijn, M.J. Tummers Files PDF Post_print.pdf 1.61 MB Close viewer /islandora/object/uuid:3d826726-15a9-4cda-9940-3f5c4ee5ddf8/datastream/OBJ/view