## 4 Result and Discussion
### Influence of Structural Parameters of Heat Exchanger on Heat Transfer Performance
#### 4.4.2 CDU Side Structure  
(1) Number of CDU chips. The condenser CDU used in the backplate heat pipe system was a brazed plate-type heat exchanger. The number of plates can be increased or decreased appropriately according to actual needs. The increase in the number of plates can increase the heat exchange area between the refrigerant and the frozen water side and increase the corresponding cost. The number of CDU condenser plates was 42, and the influence of a different number of plates on the heat transfer performance was simulated by the model. Keeping other structural parameters unchanged, the number of condenser plates was increased from 22 to 62. As can be seen from Figure 16, both the heat transfer and pressure drop increased with the increase of the number of plates, and the increasing trend gradually decreased. As the number of plates increased, the heat exchange area increased, and the heat exchange correspondingly increased. Meanwhile, the frictional resistance of the refrigerant and the flow between the plates and the corner hole increased, and the pressure drop correspondingly increased. Figure 15: The heat exchange capacity and the pressure drop in the evaporator vary with the number of slices. (2) CDU ripple amplitude. The amplitude of CDU ripple is the depth of ripple, and the size of ripple amplitude determines the flow form and heat transfer area of refrigerant between plates. The increase of ripple amplitude can enhance the mixing of vortices to some extent, but the possibility of scaling will also increase [34]. In this research, the ripple amplitude of CDU condenser was 24 mm, and the influence of different ripple amplitudes on heat transfer performance was simulated through the model. Other structural parameters were kept unchanged to increase the ripple amplitude of the condenser from 20 mm to 28 mm. As shown in Figure 17, the heat transfer increased with increasing ripple amplitude, refrigerant pressure dropped and decreased with the increment of ripple amplitude, among them, the variations in pressure drop was small, so the ripple amplitude of pressure dropped. Increased ripple amplitude is helpful to deepen the space between grooves, make the fluid turbulence degree strengthen, reduce the flow dead zone, and, correspondingly, the flow resistance is reduced, the pressure drop is reduced, and the heat transfer increased. Figure 16: Heat exchange capacity and pressure drop in the evaporator vary with the number of plates. Figure 17: Heat transfer and pressure drop in the evaporator as a function of ripple amplitude. (3) Ripple inclination of CDU. When the inclination angle is small, the fluid flows along the direction of the ripple, and the distribution of the fluid is relatively uneven. When the inclination angle increases, the inter-plate fluid flows along the ripple decrease, forming a three-dimensional flow. Turbulence increases. In this paper, the refrigerant-side heat transfer correlation of the heat transfer model reflected the correction term for the ripple inclination angle, but it was still unable to completely simulate the effect of internal popular changes on temperature and pressure field, which had certain limitations. The ripple inclination angle of the CDU condenser was 30\({}^{\circ}\), and the influence of different ripple inclination angles on heat transfer performance was simulated through the model. Other structural parameters were kept unchanged to increase the corrugation angle of the condenser from 30\({}^{\circ}\) to 70\({}^{\circ}\). As can be seen from the Figure 18, the ripple inclination angle changed from 30\({}^{\circ}\) to 60\({}^{\circ}\), and the heat exchange and pressure drop increased. When the inclination angle was greater than 60\({}^{\circ}\), the heat exchange and pressure decreased rapidly, which was the same as the trend of ripple inclination of a single plate simulated by [PERSON] et al. [35].