The common scale-up methodology for gas-solid spouted bed that has been reported in the literature is based on matching dimensionless groups. This methodology has been validated by measuring global hydrodynamic parameters and non-validated by limited point measurements of solids holdup and velocity. Therefore, the purpose of this work is to implement our advanced non-invasive gamma-ray computed tomography (CT) technique to assess and to demonstrate that the reported set of the dimensionless groups are not adequate in capturing all the interplay phenomena for achieving similarity in local solids and gas holdups cross-sectional distributions and their radial profiles along the bed height measured in 0.076 and 0.152 m spouted beds. The results clearly identified the three regions (spout, annulus and fountain) of gas-solid spouted beds and their solids structure. In addition, the reported results are valuable as a benchmarking data for CFD and DEM simulations.
A set of dimensionless groups has been proposed in the literature by He et al. [He Y. L., Lim C. J., Grace J. R., Scale-up studies of spouted beds, Chemical Engineering Science, 52 (2), 329-339, 1997] to scale-up gas-solid spouted beds while maintaining their hydrodynamics similarity. The literature reported studies do not provide conclusive assessments about this methodology. Therefore, in this work, we have applied an advanced non-invasive radioactive particle tracking (RPT) technique for the first time to evaluate such scale-up methodology by measuring the local solids velocity, normal and shear stresses and the turbulent kinetic energy. The axial and azimuthal averaged radial profiles of solids velocity, normal stresses, shear stresses, and turbulent kinetic energy illustrate that the similarity of the hydrodynamics has not been attained when the proposed set of dimensionless groups has been matched using two sizes of spouted beds of 0.076 m and 0.152 m and sets of operating conditions. The conclusion is consistent with the recent reported findings by measuring cross sectional distribution and radial profiles of solids and gas holdups along the bed height using gamma-ray computed tomography and by the limited point measurements of solids velocity and holdup using optical fiber probe. It is clear that local measurements of hydrodynamic parameters are essential for detailed assessment of scale-up methodologies. The presented results of our work in terms of the components profiles of the particles radial velocities and turbulent parameters are also valuable for benchmarking computational fluid dynamics codes and models.
The successful operation and safety of the Very-High-Temperature Nuclear Reactors (VHTR) extremely depend on the quality of the TRISO nuclear fuel coated particles. Hence, the fuel coating technology of TRISO particles, based on chemical vapour deposition (CVD) process, performed in gas-solid spouted beds, is of utmost importance. However, the deposition of the coating layers surrounding the kernel is a delicate process, and impacted by the hydrodynamics of spouted beds. Therefore, in this work, we have applied an advanced non-invasive gamma-ray computed tomography (CT) technique for the first time to investigate the hydrodynamics of spouted beds. In particular, we study the effect of particle density, particle size, bed size, and superficial gas velocity on the gas-solid cross-sectional distributions of spouted beds. The color distributions of the cross-sectional images clearly identified the three regions of spouted beds: the spout, the annulus, and the fountain regions. Interesting results and findings are presented, discussed and analyzed in the article. For example, the results demonstrated that the summation that operating spouted beds at stable spouting state would lead to achieving uniform coating layers of the particles in the TRISO fuel coating process is not adequate. Further, it has been found that increasing the superficial gas velocity much higher above the minimum spouting velocity increases the gas holdup in the annulus above the gas holdup value at the loss-packed bed state, contrary to common assumptions presented in the literature. This study represents an original experimental investigation required both for advancing the understanding of TRISO particles spouted bed and providing benchmark data to validate computational fluid dynamics (CFD).
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