Mixed-Convection Heat Transfer in Vertical Packed Channels

The experimentalresults ofmixed-convectionheat transfer in a vertical packed channelwith asymmetricheating of opposingwalls are reported. The experiments were carried out in the range of 2 < Pe < 2200 and 700 <Ra < 1500. The measured temperature distribution indicates the existence of a secondary convective cell inside the vertical packed channel in the mixed-convection regime. A correlation equation for Nusselt number in terms of Peclet number Pe andRayleigh numberRawas obtained from experimental data. A plot ofNu/Pe1/2 vs Ra/Pe exhibits the transition of heat-transfer results from the natural convection limit to the forced convection limit. The following three convection regimes exist: natural convection regime, 105 <Ra/Pe; mixed-convection regime, 1 <Ra/Pe < 105; and forced convection regime, Ra/Pe < 1. Nomenclature Acs = cross-sectionalarea of the channel Ah = surface area of the heated wall B = shape factor de ned in Eq. (5) cp = speci c heat of Freon-113 (R113) dp = sphere diameter H = plate separation of the channel K = permeability of the packed bed de ned in Eq. (7) k f = thermal conductivityof Freon-113 km = media effective thermal conductivity ks = thermal conductivityof chrome steel Nu = Nusselt number de ned in Eq. (4) Pe = Peclet number de ned in Eq. (3) qw = heat ux at the heated wall Ra = Rayleigh number in Eq. (2) Tc = temperature of the cooled wall Th = temperature of the heated wall Ti = uid temperature at inlet of the test section u i = uid velocity at inlet of the test section ®m = media thermal diffusivity,®m D km=.cp / f ¯ = thermal expansion coef cient 1T = temperature difference,1T D Th ¡ Tc ¸ = thermal conductivity ratio of k f and ks º = kinematic viscosity of Freon-113 = density of Freon-113 ’ = porosity of the packed be