Experiments support simulations by the NEPTUNE_CFD code in an Upflow Bubbling Fluidized Bed reactor

Gas-Solid Flow in a Fluidized-Particle Tubular Solar Receiver: Off-Sun Experimental Flow Regimes Characterization

“…This influence is directly presented in Figure 7 in terms of the overall solid volume fraction 𝛼 , calculated in the dense zone, versus the superficial excess air velocity in the tube 𝑈 𝑈 at the level of the aeration injection. Three curves are presented, for the following test cases: no particle circulation, and particle mass fluxes of 50 and 100 kg/m 2 s. First, the increase of the aeration flow rate induces a relatively linear decrease of 𝛼 because of an increasing air volume, as was previously observed [16,17]. This means that the fluidization regime has no influence on the proportion of the volume occupied by the air.…”

“…Figure 9a indicates that the suspension is in the single bubbling regime just above the aeration, characterized by several distributions of peaks at frequencies higher than 1 Hz with small magnitudes. Along the tube height, the bubbles coalesce to form slugs [16]. At roughly 1 m above the aeration, the frequency distribution is thus shifted to lower values and the peaks are more clearly defined at 0.4-0.5 Hz and higher magnitudes (Figure 9b).…”

“…These articles emphasize that the thermal performances of the solar receiver are strongly correlated to the hydrodynamics of the two-phase flow. Two transitions of regime have been identified in this kind of tube: from bubbling to wall slugging and then to axisymmetric slugging [16,17]. Since the formation of axisymmetric slugs result in a significant decrease of the wall-to-bed heat transfer because of a reduction of particle mixing, the identification of the fluidization regime is critical for solar applications [18,19].…”

“…Experimental set-ups were richly instrumented in thermocouples but poorly in terms of pressure probes along the receiver, which prevented the identification of the different fluidization regimes. In more recent studies, fluidization regimes were analysed by means of a highspeed camera [16,19]. However, in [19] the authors studied only a particle non-circulating configuration.…”

“…Increasing this flow rate could lead to a turbulent fluidization regime that is characterized by both a decrease of the particles volume fraction and a strong increase of the particles mixing [20]. Such regime could help to improve the heat transfer, as predicted by [16]. Such simple reasoning motivates a broadening of the range of the aeration flow rate, in order to improve the internal mixing of the suspension.…”