Multiscale modelling of wall-to-bed heat transfer in fixed beds with non-spherical pellets: From particle-resolved CFD to pseudo-homogenous models. (8th June 2021)

• Record Type: Journal Article
• Authors: Moghaddam, E.M.; Foumeny, E.A.; Stankiewicz, A.I.; Padding, J.T.
• Is Part Of: Chemical engineering science. Volume 236(2021)
• Publication Date: 2021-06-08
• Subjects: Rigid Body Dynamics -- Particle-resolved CFD Simulations -- Packing -- Raschig rings -- Effective heat transfer parameters -- Length dependency; Chemical engineering -- Periodicals; Génie chimique -- Périodiques; Chemical engineering; Periodicals; Electronic journals; 660
• DOI: 10.1016/j.ces.2021.116532
• Languages: English
• ISSNs: 0009-2509

Abstract

Graphical abstract: Highlights: Study of forced convection heat transfer through packed beds. Discrete pellet effects in narrow tubes with spheres, cylinders and Raschig rings. Significant local deviations from pseudo-homogenous model predictions. Exposition of length-dependence of effective heat transfer parameters. Abstract: We investigate forced convective heat transfer in packings of spheres, cylinders and Raschig rings, made of glass, steel and alumina, in relatively narrow tubes. A detailed comparison is made between resolved pellet-scale, azimuthally-averaged temperature profiles, and 2D-axially-dispersed pseudo-homogenous plug flow (2D-ADPF) predictions. The local temperature deviates significantly from azimuthally-averaged profiles, which in turn deviate from 2D-ADPF predictions. We show that the length dependency of effective heat transfer parameters is caused by thermal (non-)equilibrium between fluid and solid phases along the bed and not related to inadequate insulation of the calming section or the thermocouple's cross or an under-developed velocity and thermal field at the bed inlet. The influence of pellet shape and thermal conductivity and tube-to-pellet diameter ratio on ker and hw are assessed. We conclude that the models of Specchia/Baldi/Gianetto/Sicardi for all flow regimes and of Martin/Nilles for the turbulent regime are recommended for practical use for spherical particles.