## 2 Experimental Procedure and Data Reduction  
### Experimental System and Procedure  
The height of the cooling tower in this experiment is 1540 mm; the air inlet height, throat radius, mean radius of the air inlet, and radius of the top of the tower are 104 mm, 343 mm, 580 mm, and 370 mm, respectively. [PERSON] et al. [27] found that air velocities agreed under the same proportions. According to the similarity principle, the actual size of the air-cooling tower was simplified by a 1:100 proportional reduction, and then an experimental system of a SCAL-type indirect air-cooling tower was established. Experiments were conducted in a natural-wind-simulating system and water-cycling system. The schematic diagram of the experimental apparatus is shown in Figure 1, consisting of a cooling tower body, radiators, rotating wind deflectors, natural-wind-simulating system, and water-heating tank. The environmental natural wind simulation system is shown in Figure 2.  
It is difficult to perfectly satisfy the similarities for \(Re_{\text{D}}\) and \(Fr\) simultaneously in the laboratory; limited similarity conditions could be achieved between the prototype and the experimental model. The key scaling parameters used in the experimental model include the aspect ratio of the tower, crosswind speed ratio, Froude number, and Euler number [28]. Hot water was intended to provide hot fluid at 40 \({}^{\circ}\)C through the radiator tubes in the air-cooling tower. The outlet temperature of the radiators was taken by the average temperature after several experiments. Hot water flowed inside the tubes while air acted as a coolant, flowing outside the finned tubes. The wind speed in the experiment was 1/10 of the true wind speed; thus, the inlet wind velocity at the upward side of the tower, produced by the lower fan, was 0 m/s for the windless state and 0.2, 0.3, 0.4, 0.5, 0.6, and 0.8 m/s thereafter. According to the distribution of natural wind and the vertical distance between the two fans in the experiment, the top-level wind velocity produced by the upper fan was approximately 0 m/s in the windless state and 0.4, 0.6, 0.8, 1.0, 1.2, and 1.6 m/s according to previous research [27]. The inlet velocity of the air in the air-cooling tower was quite small due to natural wind, which led to a larger measurement error. The natural-wind-simulating system shown in Figure 3 was used in the experiment to increase the inlet velocity. To investigate the effect of inlet air on the cooling performance and to improve the wind environment, a rotating wind deflector system was adopted in the experimental system. A sketch of the rotating wind deflector system is shown in Figure 3, and a picture of the wind deflector is shown in Figure 4.  
Figure 1: Schematic diagram of experimental system. 1—Natural-wind-simulating system; 2—Cooling tower; 3—Wind deflector; 4—Experiment table; 5—Radiators; 6—Water tank. Figure 2: Environmental natural wind simulation system. During the experimental process, air flow from the laboratory room was induced through the wind tunnel by a small fan to pass successfully into the air-cooling tower. Hot water was driven to the air-cooled heat exchangers by a pump from a hot water tank, which could heat the water to 40 \({}^{\circ}\)C using electric heating rods (0-6 kW). The outlet temperature of the water in the heat exchangers was measured using two high-precision PT100-type thermal resistors with an accuracy of \(\pm\)0.1 \({}^{\circ}\)C. The flow rate of water into the tower was measured by a rotameter (0-15 L/min with a minimum scale of 0.01 L/min). Air velocity was measured using a KA22-type hot-wire anemometer with an accuracy of 0.01 m/s. The air temperatures of the tower inlet and outlet were measured by two sets of multi-point T-type copper-constantan thermocouple grids, respectively.