TY - JOUR
T1 - Flow and heat transfer measurements in natural convection in coarse-grained porous media
AU - Ataei-Dadavi, Iman
AU - Chakkingal, Manu
AU - Kenjeres, Sasa
AU - Kleijn, Chris R.
AU - Tummers, Mark J.
N1 - Accepted Author Manuscript
PY - 2019
Y1 - 2019
N2 - 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.
AB - 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.
KW - Heat transfer
KW - Liquid crystal thermography
KW - Natural convection
KW - Particle image velocimetry
KW - Porous media
UR - http://www.scopus.com/inward/record.url?scp=85055755800&partnerID=8YFLogxK
U2 - 10.1016/j.ijheatmasstransfer.2018.10.118
DO - 10.1016/j.ijheatmasstransfer.2018.10.118
M3 - Article
AN - SCOPUS:85055755800
SN - 0017-9310
VL - 130
SP - 575
EP - 584
JO - International Journal of Heat and Mass Transfer
JF - International Journal of Heat and Mass Transfer
ER -