## 5 Computational Analysis
### Grid Independence Study
#### 5.4.2 Inside Flow Pattern with Different Distributor Plates  
CFD simulations were carried out for 5 s for every case. Pressure drop across the bed, and minimum fluidization velocities were calculated and compared with the experimental. CFD results show good agreement with the experimental results portraying the validity of CFD model used. Qualitative results of iso-surfaces and contours of solid volume fractions revealed smaller bubbles through perforated plate distributors. Larger bubbles formed in the 45\({}^{\circ}\) distributor plate due to larger slot openings. Moreover, a blend of larger and smaller bubbles was formed in the case of hybrid plate distributors due to smaller holes and larger slots.  
It can be revealed from the above figures that CFD simulations depict the inside flow behavior of a fluidized bed. It can be observed from the contours of the solid volume fraction in Figure 17 that smaller bubbles arise from a perforated plate in contrast with a 45\({}^{\circ}\) slotted plate where larger bubbles arise through angular slots, as shown in Figure 17a,b, respectively. However, the hybrid plate portrays the relatively larger bubbles arising through 45\({}^{\circ}\) angular slots and smaller bubbles through smaller perforated holes, as shown in Figure 17c. Such behavior can be observed in the iso-surface contours of solid volume fraction in Figure 18, where smaller straight iso-surfaces illustrate the flow of air bubbles through perforated holes of perforated plate. Conversely, for 45\({}^{\circ}\) hybrid plate swirling larger iso-surfaces demonstrate the flow of air through angular plate slots exhibiting lateral mixing of solid particles and swirling pattern in shallow bed as shown in Figure 18b. However, in a deep bed, multi-layer axial-lateral rotation of solids is observed, which is also illustrated by [PERSON], 2016 [42] during his experimental work of fluidization using different distributor plates. Whereas in Figure 18c hybrid plate shows the swirling and axial flow blend due to hybrid openings (angular slots + straight smaller holes), which can also lead to more chaotic flow resulting in enhanced mixing in a fluidized bed. Likewise, velocity vectors in Figure 19 also show the flow characteristics inside the fluidized bed for different distributor plates. The perforated plate shows the uniform axial rise of fluid suspension due to smaller air bubbles rising through the central core and descending near the cylindrical walls causing an axial circulatory flow pattern as depicted in Figure 19a. The 45\({}^{\circ}\) slotted plate shows a swirling flow pattern observed by velocity vectors in Figure 19b for shallow depth. It is also pertinent to mention here that for shallow initial beds, there is a significant rise of sand bed in 45\({}^{\circ}\) slotted plate due to larger bubble size to initial bed ratio, where larger size bubbles approaching promptly to the surface of the bed resulting in significant initial bed height rise. However, deep beds with 45\({}^{\circ}\) slotted plate exhibit moderate bed rise due to smaller bubble size to initial bed ratio. The hybrid plate shows a mixed flow pattern in axial and lateral directions due to mixing swirling and straight upward flow of gas solids mixture. Due to blends of bubbles rising through the hybrid distributor plate, a moderate rise and more diverse spread of solid particles are observed through CFD simulation results in Figure 19c.  
Figure 17: Contours of solid volume fraction for shallow bed different plates at a time, t = 5 s.