## 4 Results and Discussion
### Operation Strategy  
Based on the above performance discussion of HDS, this section will give a low-energy operation strategy of HDS in the summer. Moreover, the determination of the HDS air supply parameter is the premise of designing the operation strategy.  
At present, the main cable protection requires less than 60% RH inside it, but RH is affected by temperature and moisture content. Given that moisture content is the fundamental driver of mass transfer, it should be considered a key parameter for the air supply of the main cable. When the moisture content of the air supply decreases, it will shorten the drying time and improve the effects of main cable protection. However, the moisture load and the energy consumption of the dehumidification plant will increase, accompanying a decrease in the moisture content of the supply air. The following is the calculation of the drying time in different air supply moisture contents.  
Some assumptions are made. (1) The void of the main cable is 20%. (2) The water content of the main cable is 5% of the void. (3) The leakage rate of air inside the main cable is constant at 0.005. (4) Exhaust temperature of the main cable is 18.3 \({}^{\circ}\)C, the exhaust RH is 80% and the exhaust moisture content is 10.3 g kg\({}^{-1}\), which refers to the annual average temperature and annual average RH in Suzhou, China.  
The water content per unit length of the main cable can be calculated by Equation (26).  
\[M=\frac{\pi}{4}D^{2}\varphi\theta\rho_{w} \tag{26}\]  
where \(D\) is the diameter of the main cable, \(D=0.721\) m. \(\varphi\) is the void of the main cable. \(\theta\) is the water content of the main cable. \(\rho_{w}\) is the density of water.  
Figure 10 is a schematic diagram of air leakage in the main cable. The airflow at different locations of the main cable is calculated by Equation (27).  
\[Q_{i}=Q_{0}(1-x)^{i} \tag{27}\]  
where \(Q_{0}\) is the initial airflow, \(Q_{0}=12\) m\({}^{3}\) h\({}^{-1}\). \(i\) is the distance from the injection cover, and \(x\) is the leakage rate of the air.  
Figure 9: Cooling capacity required for the aftercooler of three dehumidification systems. (**a**) Inlet air temperature. (**b**) Inlet air moisture content.  
The time of the drying phase can be calculated by Equation (28).  
\[t=\int\frac{M}{1440\times 10^{-3}Q_{i}(d_{o}-d_{i})\rho_{w}}\mathrm{d}l \tag{28}\]  
where \(l\) is the air supply distance. \(d_{o}\) is the exhaust moisture content of the main cable. \(d_{i}\) is moisture content of the main cable's air supply. \(Q_{i}\) is the airflow rate.  
The results of the calculations are shown in Table 4. When the external sheath of the main cable is partially broken, the dry air will leak to the outside. As a result, the flow rate gradually decreases in the main airflow direction, which will reduce the dehumidification efficiency and extend the drying time of the main cable. Therefore, when air leakage occurs, the airflow rate should be increased to ensure the dehumidification effect. Drying time is generally one year, based on the design experience of the suspension bridge dehumidification system. Therefore, considering the anti-corrosion effects, energy consumption and drying time, the moisture content corresponding to the exhaust temperature and RH of 45% should be used for the air supply on a suspension bridge.  
Based on the air supply parameters and the analysis of performance in Section 4.1, the low-energy operation strategy of HDS in summer cases of a suspension bridge is shown in Table 5.