# CFD Simulation of Dry Pressure Drop in a Cross-Flow Rotating Packed Bed
## 4 Results and Discussion
### Packing Zone  
#### 4.3.1 Effect of Rotating Speed  
The effect of rotating speed on the pressure drop in the packing zone is shown in Figure 7. Figure 7a shows that as the rotating speed increases from 200 rpm to 1000 rpm, the pressure drop at the gas flow rate of 200 m\({}^{3}\cdot\)h\({}^{-1}\) decreases to a minimum of 0.2 Pa, because the energy overcomes the frictional force caused by packing, after which it increases rapidly to 6 Pa because of the increase of gas kinetic energy by rotating. However, the pressure drop decreases significantly from 16.5 Pa to 6 Pa at a gas flow rate of 800 m\({}^{3}\cdot\)h\({}^{-1}\).  
Figure 7b shows that static pressure drop increases slowly at a low rotating speed of 600 rpm because of the conversion of static pressure energy to kinetic energy. Then, the packing zone is subdivided into two parts: Section 1 (plane a\({}_{3}\) to plane a\({}_{4}\)) and Section 2 (plane a\({}_{4}\) to plane a\({}_{5}\)). In Section 1, at a gas flow rate of 200 m\({}^{3}\cdot\)h\({}^{-1}\) and rotating speed of 400 rpm, the static pressure drop increases to a maximum of 2 Pa and then decreases to \(-\)5 Pa at a rotating speed of 1000 rpm (Figure 8a). The reason can be explained as follows. The gas velocity in the lateral direction increases more quickly than that in the vertical direction due to the friction of packing, and the gas moves mainly in the lateral direction and collides with the wall, leading to the conversion of kinetic energy to static pressure energy. This is also confirmed by the static pressure cloud. To be more specific, the pressure drop at the edge of the packing area is larger than that in surrounding areas (red color shown in Figure 8c,d). In Section 1, at the gas flow rate of 800 m\({}^{3}\cdot\)h\({}^{-1}\) and rotating speed of 400 rpm, the static pressure drop is kept constant and then increases to 18 Pa at a rotating speed of 800 rpm, which may be attributed to the initial gas distribution. There would be a balance between the increase of static pressure energy by collision and the conversion to kinetic energy at low rotating speeds, and the latter is predominant over the former with the increase of the rotating speed. In Section 2, the static pressure drop goes up to 17 Pa at  
Figure 5: The effect of rotating speed on the pressure drop in cavity zone A. (**a**) Pressure drop; (**b**) static pressure drop; (**c**) dynamic pressure drop.  
the gas flow rate of 800 m\({}^{3}\cdot\)h\({}^{-1}\) as the rotating speed is increased from 200 rpm to 1000 rpm due to less collision.  
Figure 7c illustrates that dynamic pressure drop first decreases to \(-\)4 Pa and then increases to 2 Pa when the gas flow rate and rotating speed are kept at 200 m\({}^{3}\cdot\)h\({}^{-1}\) and 400 rpm, respectively. Finally, it decreases from 2.5 Pa to \(-\)28 Pa at gas flow rate of 800 m\({}^{3}\cdot\)h\({}^{-1}\). As shown in Figure 9, the dynamic pressure drop in Section 1 decreases gradually both at low and high gas flow rates, while that in Section 2 increases with the increase of rotating speed from 200 rpm to 800 rpm due to the conversion of more static pressure energy to kinetic and internal energy.