# Heat Transfer Performance and Flow Characteristics of Helical Baffle-Corrugated Tube Heat Exchanger
## 3 Results and Discussion
### Helix Angle and Heat Transfer Performance
The total heat transfer coefficient of the heat exchanger is an important evaluation indicator, and the total heat transfer coefficient \(K_{C}\) of the helical baffle heat exchanger can be calculated by Equation (7):  
\[\left\{ \begin{array}{l}\frac{1}{K_{c}}=\frac{D_{h}}{d_{h}K_{b}}+\frac{1}{K_ {s}}+R_{w}\\ R_{w}=\frac{b}{\lambda}\end{array} \right. \tag{7}\]  
where \(d_{h}\), \(D_{h}\) are the inner and outer diameters of the heat exchanger tube, \(K_{s}\), \(K_{h}\) are the heat transfer coefficients of the shell and tube, \(R_{w}\) is the thermal resistance of the wall of the tube, \(b\) is the thickness of the heat exchanger tube, and \(\lambda\) is the thermal conductivity of the tube. As can be seen in Figure 7a, the total heat transfer coefficients of helical baffle heat exchangers with different helix angles all increase with the increase in the shell flow rate, and the improvement ranges from 30.80% to 38.91%. When the shell flow rate is the same, reducing the helix angle can effectively improve the total heat transfer coefficient of the heat exchanger. In this study, when the helix angle is reduced from 28.42\({}^{\circ}\) to 10.81\({}^{\circ}\), the overall improvement is around 20%. The shell heat transfer coefficients per unit pressure drop corresponding to different helix angles are shown in Figure 7b. The shell heat transfer coefficient per unit of pressure drop decreases with the decreasing helix angle. When the  
Figure 5: Simulation results for shell volume flow rate equal to 7.5 m\({}^{3}\)/h: (**a**) velocity; (**b**) pressure. shell flow rate is small, i.e., there is a weaker degree of turbulence, the shell heat transfer coefficient per unit of pressure drop decreases significantly with the decreasing helix angle. In this study, when the shell volume flow rate is increased from 3.5 m\({}^{3}\)/h to 7.5 m\({}^{3}\)/h, comparing the helix angle of 28.42\({}^{\circ}\) with 10.81\({}^{\circ}\), it is found that the percentage of reduction in the shell heat transfer coefficient per unit pressure drop decreases from 86% to 75%. It is also found in Figure 7 that when the total heat transfer coefficient is similar, the larger the helix angle is, the larger the shell heat transfer coefficient per unit of pressure drop is. This is because in the helical baffle heat exchanger, the fluid flows in the form of a helical plunger, and the smaller the helix angle is, i.e., the smaller the cross-sectional area of the fluid flow is, the smaller the axial component of its velocity, the larger the radial component, the larger the tangential component, and the stronger the effect of transverse flow. The helical flow of the bundle of the tube scouring is closer to the transverse scouring, which improves the overall turbulence level and achieves the purpose of destroying the  
Figure 6: Velocity streamline for shell volume flow rate equal to 7.5 m\({}^{3}\)/h. Figure 7: Comparison of heat transfer coefficients for different helix angles: (**a**) total heat transfer coefficient; (**b**) shell heat transfer coefficient per unit pressure drop. boundary layer near the wall of the tube, thus increasing the convection heat transfer intensity of the shell process. However, at the same time, the disturbance of the flow field generated by the tube bundle and the resistance brought by the baffle will also be stronger, resulting in a larger pressure loss.