## 4 Results and Discussion
### Effect of Crosswind on Performance with Rotating Wind Deflectors  
To reduce the influence of crosswind on the cooling tower, wind deflectors were installed on a motor-driven rotary support. The rotating velocity was controlled by a transmission. The air flow rate and heat transfer rate of the tower were obtained from the numerical results when the crosswind velocity was 5 m/s with eight wind deflectors. The temperature contours at the tower inlet with various rotating velocity for the wind deflectors are shown in Figure 19 at a crosswind speed of 5 m/s.  
Figure 17: Air flow rate and heat transfer rate versus number of wind deflectors.  
Figure 18: Temperature contours at the tower inlet (unit: K). (a) 4 deflectors, (b) 8 deflectors.  
Variations in the air flow rate and heat transfer rate of the cooling tower with different rotating velocities with four and eight wind deflectors at a wind speed of 5 m/s are shown in Figure 20. The air flow rate decreases continuously, while the heat transfer rate decreases to the minimum at a rotating velocity of 2 r/min with eight wind deflectors and 4 r/min with four wind deflectors. The entrance of outside air into the tower is prevented by the wind deflectors with a lower rotation speed, which seriously affects the radiator heat transfer. The heat transfer rate of the cooling tower with eight wind deflectors begins to increase as the rotating velocity of the wind deflectors exceeds 2 r/min, while that with four deflectors begins to increase when the rotating velocity is over 4 r/min.  
Figure 19: Temperature contours (unit: K) at the inlet of tower with various rotating velocity for wind deflectors under 5 m/s wind speed.  
Figure 20: Air flow rate and heat transfer rate versus rotating velocity of four and eight wind deflectors under 5 m/s crosswind speed.  
Furthermore, the air is disturbed by the rotating deflectors at the bottom of the tower. In the present study, the air flow rate is positive when air flows from the bottom to the top of the tower and negative when air flows from the top to the bottom in the tower. Figure 20 shows that when the air is disturbed by the rotating deflectors, the air flow rate becomes negative when the rotating velocity is higher than 2 r/min with eight deflectors or higher than 4 r/min with four deflectors, indicating that the air flow direction moves from top to bottom. The heat transfer rate increases with an increasing absolute value of the air flow rate.  
The numerical simulation results of the thermal efficiency coefficients of the cooling tower with rotating wind deflectors are shown in Figure 21. The thermal efficiency coefficients grow with the increment of the rotating velocity when it exceeds 2 r/min.  
With eight wind deflectors, the effect of heat transfer from the radiators improves as the rotating speed increases to over 2 r/min. Thereafter, the wind direction in the tower reverses as the rotating speed increases. As the rotating speed accelerates, the suction effect becomes stronger, similar to a wind machine. Then, heated air is removed from the tower. Thus, the thermal-hydraulic and cooling performance of the air-cooling tower is enhanced by rotating wind deflectors.  
However, the economic benefit of rotating wind deflectors is mainly determined by heat transfer enhancement and power consumption from the driving motor. For example, the motor power is approximately 3 kW when driving a gear of 400 kg rotating at a speed of 5 r/min, and the heat transfer rate can be increased by 33.9% according to Figure 20 whereas motor power loss is negligible.