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

Abstract

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 0.72m long tube containing 1000 spheres (N=5.45) and a 0.35m 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 0.20m 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 0.16m 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.