# Heat Transfer Performance and Flow Characteristics of Helical Baffle-Corrugated Tube Heat Exchanger
## 3 Results and Discussion  
### Helix Angle and Heat Transfer Performance  
The structure of a continuous helical baffle plays a crucial role in strengthening the heat transfer performance of a heat exchanger. The continuous helical baffle has a helical surface, and the shell diameter determines the main structural parameters for the helix angle. Changing the same shell diameter under the pitch in essence is to change the helix angle. The definition of a helical angle is shown in Equation (6). \[\beta=\arctan(\frac{H_{s}}{\pi d_{s}}) \tag{6}\]  
where \(\beta\) is the helix angle, \(H_{s}\) is the pitch of the helical baffle, and \(d_{s}\) is the helical diameter. In this work, the pitches of the continuous helical baffle are 60 mm, 80 mm, 100 mm, 130 mm, and 170 mm, and the corresponding helix angles are 10.81\({}^{\circ}\), 14.29\({}^{\circ}\), 17.66\({}^{\circ}\), 22.48\({}^{\circ}\), and 28.42\({}^{\circ}\), respectively. The change in helix angle corresponds to the change in baffle structure, which mainly affects the distribution of the heat exchanger shell flow field. The shell-stream volume flow rates of 3.5 m\({}^{3}\)/h, 4.5 m\({}^{3}\)/h, 5.5 m\({}^{3}\)/h, 6.5 m\({}^{3}\)/h, and 7.5 m\({}^{3}\)/h were selected, keeping the tube-stream volume flow rate of 4 m\({}^{3}\)/h unchanged. Simulations were carried out for different shell volume flow rates, and the results for a shell volume flow rate of 7.5 m\({}^{3}\)/h are shown in Figure 5. From Figure 5a, it can be seen that in the helical baffle heat exchanger with a larger helical angle, there is a phenomenon of sudden increase in the diagonal distribution velocity at the outlet position due to the sudden reduction in the fluid circulation area and change in the flow direction. While the helical angle is smaller, the axial velocity of the shell fluid in the direction of the extended center axis is smaller and closer to the transverse flow, so the smaller the helical angle of the helical baffle heat exchanger, the smaller the change of flow velocity at the exit. The  
Figure 4: Comparison between experiment and simulation result: (**a**) heat transfer coefficient; (**b**) pressure drop. pressure results of helical baffles with different helical angles are illustrated in Figure 5b, and it can be seen that the smaller the helical angle, the greater the axial pressure drop of the helical baffle heat exchanger. A comparison of the velocity streamline of helical baffle heat exchangers with different helical angles is shown in Figure 6, and the results show that fluid stagnation zones exist in the inlet and outlet sections of helical baffle heat exchangers with different helical angles. In addition, clear vortices exist near the shell inlet when \(\beta\) equals 17.66\({}^{\circ}\), 22.48\({}^{\circ}\). This is due to the fact that in the inlet section, the fluid flows vertically and axially from the shell process inlet and is affected by the disturbing effect of the tube bundles and the influence of the larger circulation area, which makes the flow velocity decrease rapidly, impacts the tube bundles and the shell process wall, and produces a reflux zone near the inlet area. In the exit section, the shell process fluid, due to the exit of the flow cross-sectional area and the reduction in the exit to produce acceleration, the vast majority of the fluid shows normal outflow. Due to the disturbing effect of the tube bundle, a small portion of the fluid will flow back in the exit section at the shell angle, forming a flow dead zone. Combined with Figure 5a, it can be seen that with the reduction in the helical angle, the different helical angle of the helical baffle heat exchanger shell process fluid retention area is more obvious, but the smaller the helical angle, the smaller the shell process inlet and outlet section of the area, so that the inlet and outlet section of the fluid retention area is smaller.