# Investigation of the Fluid Flow in a Large Ball Valve Designed for Natural Gas Pipelines
## 3 Results and Discussion
### 45\({}^{\circ}\) Closure Angle  
In this case, the methane enters the internal cavity of the secondary body of the ball valve from the upstream pipe and tries to disperse inside the entire valve.  
As can be observed in Figure 6, the gas hits the sealing surface between the sealing seat and the ball, i.e., the so-called upstream sealing zone. In this area, chaotic movement of particles starts, and the first local loss of pressure from 6.3 MPa to 6.15 MPa can be observed. The trajectories deviate downstream because the gas has to pass through the sealing area to enter the cavity of the ball. This is the second zone where the pressure decreases; the  
Figure 4: Pressure line trajectories for a 30\({}^{\circ}\) closure angle: (**a**) upstream view; (**b**) downstream view.  
Figure 5: Velocity line trajectories for a 30\({}^{\circ}\) closure angle: (**a**) upstream view; (**b**) downstream view.  
pressure changes from 6.15 MPa to 5.9 MPa, the agitation phenomenon begins, and vortices are generated. Downstream, the gas particles regroup and are further driven by the main fluid flow to leave the cavity of the ball through the downstream secondary body, with a pressure of 5.9 MPa.  
The velocity line trajectories presented in Figure 7 show that the first modification of velocity from 20 m/s upstream in the pipe can be noticed at the upstream sealing zone, when the fluid starts to show chaotic movement. The gas hits the ball and the sealing surface at a velocity of almost 40 m/s. The highest velocity rate is reached in the cavity of the valve, where the agitation phenomenon of the gas particles leads to it reaching almost 90 m/s. The different trajectories and rates of velocity in the internal area of the ball and in the superior and inferior extremities of the internal wall are caused by the external geometry of the ball. The gas has the highest velocity in the cavity of the ball (yellow and orange color) and the lowest at the extremities (blue color). The pressure decreases, and the generation of the vortex determines the increase in the energy loss, both because of the size and because of the deviation in the trajectories due to the position of the valve. If the ball valve is used at a 45\({}^{\circ}\) closure angle, the pipe system needs more energy to maintain the same volumetric flow rate, because of the restricted valve opening. The greatest negative impact can be observed on the upstream seat, because the gas particles--which can contain some impurities in their composition--hit the surface of the sealing seat violently. The area of contact between the seat and the surface of the ball, denoted as A in Figure 7, is vulnerable to rapid destruction. The result is the separation of the coating material of the seat (i.e., the tungsten carbide).  
Figure 6: Pressure line trajectories for a 45\({}^{\circ}\) closure angle: (**a**) upstream view; (**b**) downstream view.  
Figure 7: Velocity line trajectories for a 45\({}^{\circ}\) closure angle: (**a**) upstream view; (**b**) downstream view.  
Moreover, it may be observed that not all of the particles have the same velocity--some of them keep moving at 20 m/s. Once they leave the turbulent zone containing a vortex, the velocity decreases to 10-15 m/s. In the zone denoted as B in Figure 7, the gas hits half of the downstream sealing seat and a part of the internal cavity of the ball, making this seat also vulnerable to rapid destruction. The vortex size can be estimated by comparison to the dimensions of the ball. Some vortices can fill almost all of the internal zone of the ball, meaning that perturbations are important and local energy losses are significant. According to [PERSON] et al., \"In general, the inlet velocity and the valve opening play very important roles to the performance of a ball valve\" [15]. Downstream of the valve, the velocity stabilizes at a rate of 20 m/s--the same as the upstream velocity in the pipe.