Effects of structural parameters on gas-solid flow and bubble characteristics in indirect fluidized bed particle solar receivers

The two-phase flow and bubble characteristics in Fluidized Bed Particle Solar Receivers (FBPSRs) with varying receiver diameters were numerically investigated by employing the Eulerian-Eulerian framework. Comparisons of solid volume fraction were made between experimental measurements and numerical simulations to validate the accuracy of the numerical model. Subsequently, the effects of receiver diameter on fluidization behavior were studied by considering particle volume fraction, slip velocity, bubbling frequency, bubble size, and bubble dynamics. The results show that a significant reduction was observed in solid holdup at z = 950 mm within narrower tubes. Besides, a consistent pattern of fluidization was evident, characterized by the formation of larger bubbles or slugs in D = 28 mm and 34 mm receivers. The larger diameter receiver restricted the size of the bubbles, leading to increased solid holdup and thus improving the contact between gas and particles. With the decrease of receiver diameter, the dominant frequency became clear. For the bubble dynamics, the bubble time fraction increased with tube diameter, but this trend became less consistent at higher elevations. Additionally, the overall bubble duration time increased with receiver diameter due to lower gas-solid slip velocity. However, a significantly higher bubble duration time was observed at z = 950 mm.