## 4 Results and Discussion  
Variations in the Total Thermal Resistance and Areal Thermal Resistance of the Thermosyphon with Respect to the Inclination Angle  
Figure 4 shows the response of the total thermal resistance with respect to the inclination angle when the thermosyphon is operating under steady-state heat transfer conditions. When the inclination angle is less than 60\({}^{\circ}\), the thermal resistance of the thermosyphon decreases with increasing inclination angle. When the inclination angle is greater than 60\({}^{\circ}\), the change in thermal resistance with the inclination angle is relatively slow. These phenomena occur because, when the inclination angle is small, increasing the inclination angle can obviously increase the actual heating area of the evaporation section of the thermosyphon and increase the gravitational component of the working fluid reflux. In contrast, when the inclination angle is sufficiently large, the gravitational force can provide power for working fluid reflux. Therefore, further increases in the inclination angle have little effect on thermal resistance. When the heat transfer power is 30 W, 40 W or 50 W, the thermal resistance is minimized when the inclination angle is 60\({}^{\circ}\). This minimum value occurs because there is sufficient gravitational force to promote the working fluid reflux, and the stratified flow of gas and liquid avoids the rising gas obstructing the working fluid reflux. The change in thermal resistance with inclination angle is in accordance with the results already published in the literature [15]. Figure 5 shows the response of the thermosyphon's areal thermal resistance with respect to the inclination angle. Overall, the areal thermal resistance does not decrease or increase with variations in the inclination angle because the areal thermal resistance is affected by the change in actual heating area generated by the change in inclination angle. Both the total thermal resistance and areal thermal resistance increase with increasing heat transfer rate. Figure 4: Relationship between the total thermal resistance and inclination of the thermosyphon. Variations in the Total Thermal Resistance and Areal Thermal Resistance of the Thermosyphon with Respect to the Heat Transfer Rate  
Figure 6 shows the response of the total thermal resistance of the thermosyphon with respect to the heat transfer rate under steady-state conditions. The general trend of the total thermal resistance of the thermosyphon is to increase with the increasing heat transfer rate, and the thermal resistance at an inclination angle of 15\({}^{\circ}\), which is greater than those at other inclinations. This maximum value of thermal resistance occurs at 15\({}^{\circ}\) because the actual heating area of the thermosyphon's evaporation section of the thermosyphon is the smallest at this angle, and the gravitational component driving the refrigerant reflux is the smallest when the inclination angle is small. This result is in accordance with the results already published in the literature [17; 23]. Figure 7 shows the response of the areal thermal resistance of the thermosyphon with respect to the heat transfer rate. The variations in the areal thermal resistance with respect to the heat transfer rate are consistent at all inclination angles, indicating that the working inclination angle has little effect on the areal thermal resistance. The overall trend of the areal thermal resistance of the thermosyphon is to increase with increasing heat transfer power, which is linearly related to the heat transfer rate. Figure 5: Relationship between the areal thermal resistance and inclination of the thermosyphon. Figure 6: Relationship between the total thermal resistance and heat transfer rate of the thermosyphon. Derivation and Verification of the Theoretical Formula for the Total Thermal Resistance of the Thermosyphon  
Figure 8 shows a primary curve fitting of the areal thermal resistance and heat transfer rate of the thermosyphon, which has a goodness of fit R\({}^{2}\) of 0.9892.