# Model Experimental Study on De-Icing Method of Bridge Pylon Beam Based on Electric Heating
## 4 Results and Analysis of De-Icing Tests
### Anti-icing Tests
#### 4.1.2 Suggested Pre-Heating Time  
Giving the suggested pre-heating time can help to save electrical energy. Combined with the temperature rise rule of the heating system, the time \(t_{p}\) required to reach the critical anti-icing temperature can be obtained. Then, the pre-heating time is controlled within \(t_{p}\pm 2\) min in order to conduct five anti-icing tests to reduce the occasionality. Finally, the final anti-icing effects of the different tests are compared, and the suggested pre-heating time is given in a combination with the temperature change of the heating system at the \"freezing moment\" (the freezing moment means the moment when the surface of the heating system begins to icing under the no pre-heating condition, it can be concluded from Section 4.1.1 that the freezing moment is 3 min)  
The specific method is as follows. The critical anti-icing of the heating system at \(-15\)\({}^{\circ}\)C ambient temperature is 1.12 \({}^{\circ}\)C. Combined with the temperature rise law of the heating system, it can be concluded that the time required to reach close to 1.12 \({}^{\circ}\)C is 5 min (as shown in Figure 12b). Therefore, 5 min was used as the basic pre-heating time to conduct anti-icing tests. Then, four groups of anti-icing tests with pre-heating durations of 3, 4, 6, and 7 min were conducted for comparison. The ambient temperature was \(-15\)\({}^{\circ}\)C; the wind velocity was 0; the precipitation was 1 mm/min; and the rainfall time was 120 min. The effects of the five sets of anti-icing tests are shown in Figure 13a, and the temperature of the heating system at 3 min (freezing moment) in each anti-icing test is shown in Figure 13b. The start time of rainfall was recorded as the initial time moment.  
In the five sets of anti-icing tests with different pre-heating times, after 120 min of spraying, there was no ice accumulation on the front surface of the heating system and no icicles attached to the bottom. This indicates that the anti-icing effect can be achieved by pre-heating the heating system. However, a large amount of ice accumulated on top of the heating system. As the pre-heating time increased, the ice accumulation on the top decreased. The reason may be that the short pre-heating time failed to transfer enough temperature to the top of the heating system, resulting in a large ice accumulation. Therefore, an optimized compensation scheme to solve the top ice accretion is proposed in Section 4.1.4.  
It can be seen in Figure 13b that with the increase in the pre-heating time, the temperature of the heating system at the 3 min moment (freezing time) gradually increases. When the pre-heating times are 3 and 4 min, the temperatures at the freezing times are lower than the critical anti-icing temperature. It means that when the pre-heating time is less than 5 min, there is still the possibility of freezing on the surface of the heating system. In the latter three pre-heating anti-icing tests, the temperatures of the heating system at the freezing time all exceeded the critical anti-icing temperature.  
Lower pre-heating times carry the risk of icing, while higher pre-heating times cause energy waste [3]. In general, the pre-heating time of the heating system is recommended to be no less than 7 min under windless conditions.  
Figure 13: (**a**) Anti-icing effects under different pre-heating times; (**b**) variation of temperature at freezing moment with the pre-heating time.