(458f) Experimental Validation of High Reynolds Number CFD Simulations of Heat Transfer in a Pilot-Scale Fixed Bed Tube

The simulation of detailed flow and transport inside the interstitial space of packed tubes using computational fluid dynamics (CFD) is becoming a standard approach to obtaining insight into fixed bed transport phenomena. At the high flow rates of industrial practice, flow and heat transfer are highly turbulent and complex, and comparisons to experiment are necessary. In this study, 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 0.16 m 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. Verification with a medium and a fine mesh showed negligible difference between the profiles.

            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.