Computational Fluid Dynamics Studies of the Effects of Temperature-Dependent Physical Properties on Fixed-Bed Heat Transfer

Abstract

The influence of the temperature profile on the fluid flow and heat transfer in a fixed bed of tube to particle ratio of 2.86 was studied by solving the 3D Navier−Stokes and energy equations by means of a commercial finite element code, ANSYS/FLOTRAN. The geometry model, representing a fixed bed, consisted of an arrangement of eight spheres in a tube. The difference in heat-transfer parameters between a wall-cooled and wall-heated reactor was studied, using air as a fluid. The dimensionless wall heat-transfer coefficient, Nu w, and the radial effective conductivity ratio, k r/k f, were evaluated from the calculated temperatures at different locations in the bed by comparing these with the analytical solution of a two-dimensional pseudohomogeneous model, using a nonlinear least-squares analysis. Results were obtained for Reynolds numbers in the range 9−1450. Though for high Re there was no real difference between a wall-cooled or a wall-heated tube, for low Re a significant difference was found. The effect of the viscosity, conductivity, and density variations, as a consequence of temperature variations, was studied using a hydrocarbon mixture as the fluid. Results indicated that the temperature profile had an influence on the fluid and heat flow and thus on the effective parameters, although at high Re numbers the influence became less.

CFD study of fluid flow and wall heat transfer in a fixed bed of spheres

“…One of the most important parts of CFD modeling is the construction of the mesh topology. In our earlier studies (Derkx and Dixon, 1996; Logtenberg and Dixon, 1998a, b; Logtenberg et al, 1999) the mesh density was investigated extensively. Additional studies were done to find the optimal mesh density, for the specific simulation geometries used here.…”

“…Earlier studies in our group used a 3‐D three‐sphere model (Derkx and Dixon, 1996), followed by an eight‐sphere model (Logtenberg and Dixon, 1998a, b) in which the packing was modeled as two layers of four spheres, perpendicular to the flow in the tube with a tube‐to‐particle diameter ratio, N = 2.43. Subsequently, a 3D 10‐sphere model was developed, with N = 2.68, incorporating contact points between the particles and between the particles and the wall (Logtenberg et al, 1999).…”

Computational Fluid Dynamics Modeling of Gas‐Liquid Two‐Phase Flow around a Spherical Particle

“…According to the information from the particle scale (film thickness), CFD simulations can then be conducted on a large scale. Other works like those of Arbogast et al [30], Logtenberg and Dixon [31], Logtenberg et al [32], Nijemeisland and Dixon [25], Dixon and Nijemeisland [26], and Magnico [33] showed the feasibility and efficiency of this type of approach. The approach is consistent with the so-called slit model concept proposed by Holub et al [34,35] and Iliuta and Larachi [36].…”

Heat conduction in granular materials

“…Goddard, 1992 and for the determination of proper bound-Ž ary conditions u Bauer and Schlunder, 1978;Cheng et al, . 1999;Logtenberg and Dixon, 1998;Gunn et al, 1987 . Moreover, it is difficult to discern how or if these methods can be made amenable to situations where the microstructure may change with time in a way which is not known a priori ᎏthat is, in a granular flow.…”