## 5 Computational Analysis
### Grid Independence Study
#### 5.4.3 Velocity Distribution of Solid Particles within a Fluidized Zone of a Gasifier  
The mean velocity distribution of solid particles with different distributor plates has been observed using CFD analysis. Solid phase velocity distribution is noted both qualitatively and quantitatively on different cut planes (z) along the height of the gasifier. It can be observed in Figure 10 that three cut planes describes the velocity distribution of sand particles with a graphical representation along with contours of velocity magnitude. Figure 20a shows that in a perforated distributor plate, the velocity distribution is axial dominant near the distributor plate due to 90\({}^{\circ}\) straight numerous smaller holes, which causes small velocity peaks as observed in graph of Figure 20a and contours of Figure 20b. however as we ascend upward there is a coalescence of smaller bubbles to form relatively larger bubbles as can be seen in Figure 10d and at the middle section there is a drift of solid particles in an upper direction along the periphery of gasifier as can be seen in Figure 20c. At the upper portion (z/z\({}_{\text{s}}\) = 0.8) of the fluidized bed, there is a sinusoidal pattern of velocity distribution due to the further coalescence of bubbles to form ever larger ones and forming relatively broader peaks of velocity distribution, indicating the wavy pattern near the surface of the fluidized bed as shown in Figure 20e,f. By employing a 45\({}^{\circ}\) slotted distributor plate, it can be inferred from the above graphs of Figure 21 that at a lower portion of the bed, and there is a start of swirling flow of solids as indicated by Figure 21b. The velocity peaks of the solid phase are not as sharp as observed for the perforated distributor plate. This effect is due to the larger openings of entering air causing bulk solids to lift at once, as shown in Figure 21a. In the middle section of the fluidized region, there is a precise observation of the swirling of solid particles, which can be observed from the graph of Figure 21c, in which there are two zones of velocity distribution. One is the lower velocity zone indicating the frequent smaller up and down of velocities of the solid phase, indicating the dominant swirl  
Figure 19: Velocity vectors of sand for different plates for shallow depth at the time, t = 5 s.  
Figure 18: Iso-surface of solid volume fraction for different plates for shallow depth at the time, t = 5 s.  
two-dimensional flow (axial + lateral) and the second zone can be indicated by peaks of solids velocities which are above the slots through which air is entering and exhibiting higher air flux as shown in Figure 21d. Velocity distribution at the upper zone of the bed exhibits more swirl dominant flow and higher axial flux as indicated by the orange color contours above the eight 45\({}^{\circ}\) slots, also expressed by broader peaks of a graph in Figure 21e and besides also spread region of emulsion phase with relatively lower velocity magnitude of a solid phase (Figure 21f). A similar effect was also observed by [PERSON] and [PERSON], 2019 by investigating two types of distributor plates, conventional distributor plate (CDP) and swirl distributor plate (SDP), for mixing characteristics. They revealed that better mixing is observed regarding the lateral distribution of solids with SDP with a dominant swirling motion of solids within a fluidized bed. Figure 20: _Cont._  
Figure 21: Cont. Figure 20: Graph and contours of the mean velocity of sand particles [m/s] with Perforated plate. In a hybrid plate, a mixed velocity distribution pattern is observed at the lower bed portion, where sharp but relatively broader peaks compared to the perforated plate are observed due to the mixing of smaller bubbles with the dominant axial flow and larger bubbles arising through 45\({}^{\circ}\) slots. These bubbles coalesce and collapse, resulting in a more chaotic flow, as shown in Figure 1(a),b.