Experimental validation of high Reynolds number CFD simulations of heat transfer in a pilot-scale fixed bed tube

CFD simulations of heat transfer in fixed beds of spheres were validated by comparison to experimental measurements in a pilot-scale rig. The comparisons were made for particle Reynolds numbers in the range 2200 < Re <27000 for tube-to-particle diameter ratio N = 5.45, and in the range 1600 < Re < 5600 for N = 7.44. Radial temperature profiles were obtained at four axial positions in the heated bed spaced 0.16m apart. CFD models of a 0.72 m long tube containing 1000 spheres (N = 5.45) and a 0.35 m long tube of 1250 spheres (N = 7.44) were solved to obtain well-developed flow fields. These provided inlet velocity profiles to reduced models of 0.20 m heated packed length, consisting of 304 spheres for N = 5.45 and 722 spheres for N = 7.44. The measured temperature profiles were used as inlet boundary conditions and profiles 0.16 m downstream were computed. A mesh verification study showed negligible difference between the profiles from a medium and a fine mesh. Contact points were treated by one of three methods: global reduction of sphere size resulting in gaps, or local insertion of bridges at particle-wall contact points with either surface flattening or bridges at the particle-particle contact points. The gaps method gave slightly poorer results; the two bridges methods were better and indistinguishable from each other. CFD simulations compared well to the experimental data: trends with Re, N and bed depth were captured, and quantitative agreement of temperature profiles was reasonable. (C) 2012 Elsevier B.V. All rights reserved.