## 3 Characteristics of Ice Accretion on Diverse Members  
### Ice Accretion on Pipeline  
#### 3.1.1 Influence of Pipeline Diameter  
The profiles and side views of the ice accretion on pipelines with various diameters for \(N=160\) are shown in Figure 5. The droplets impinged smoothly upon the cylinder. Glaze ice accretion (smooth surface) was produced, and vertical icicles hung on both sides of the cylinder. The heat absorbed by the air was less than the latent heat produced due to the freezing of all the impinging droplets. Only a portion of droplets could freeze into radial ice on the pipeline surface, and the residual droplets then froze into icicles or were dragged away under the combined action of the aerodynamic force, gravity, and surface tension. The icicle hanging from the bottom of the cylinder was in accord with the results in [PERSON] et al. [26] under small wind speed. However, icicles with an impact angle were produced in [16; 41] since the runback water under the windy condition, and icicle hanging from the bottom of the cylinder tends to disappear gradually as the airstream  
Figure 4: Symbol definition of ice accretion on pipeline. velocity increased [26], the difference from previous results could be ascribe to the large wind speed. Pipelines with \(D\leq 50\) mm had no evident curved part, which was correspond with the icicle model on transmission lines [16; 26; 41]. For pipelines with \(D>50\) mm, the transverse width and length of the curved part increased with increasing \(D\), while the longitudinal width was almost 5 mm. Consequently, the shape of the curved part resembled a sickle. Figure 5: Profiles and side views of ice accretion on pipelines (\(N=160\)): (a) \(D=25\) mm, (b) \(D=50\) mm, (c) \(D=100\) mm, (d) \(D=150\) mm, (e) \(D=200\) mm, (f) \(D=300\) mm, (g) \(D=400\) mm, (h) \(D=600\) mm, (i) \(D=800\) mm, and (j) \(D=1000\) mm. The radial ice sizes for pipelines with various diameters are shown in Figure 6. Figure 6a shows that the icing range of radial ice \(\mu\) was non-uniform and decreased with increasing \(D\). The radial ice thickness \(\delta_{0}\) (Figure 6b) decreased with increasing \(D\). \(\delta_{0}\) and \(D\) approximately followed an exponential relationship: \(\delta_{0}=a\times D^{b}\). The values of \(\delta_{0}\) were almost the same for the pipelines with various diameters in the early stage (e.g., \(N<40\) in the experiment), while \(\delta_{0}\) increased in a similar manner with increasing \(N\) after the pipelines accreted a thin layer of ice. This suggested that the ice thickness differences mainly developed in the later stage (e.g., \(N\geq 40\) in the experiment). This can be explained as follows: (1) in the early stage, the area receiving droplets was proportional to the diameter, that is, to the amount of water contained along horizontal projected area of the cylinder, and consequently, the ice thicknesses for different \(D\) values developed at a similar speed; (2) at the later stage, the surfaces were covered by a thin layer of ice accretion, and the size effect of the ice accretion likely occurred because the Nusselt number depends on the Reynolds number, resulting that the heat transfer relates to \(D\); (3) the collision efficiency of the droplets was smaller for large obstacles than for small ones. In summary, the ice sizes were closely related to the cylinder diameter, and the smaller diameter cylinder was more easily covered by ice. For the present tests, the parameters \(l\) and \(s\) of icicles for different diameter cases were determined as shown in Figures 5 and 7. There were remarkable non-uniformities of \(l\) and \(s\). The non-uniformity of \(l\) was a consequence of the variations in \(s\), which was due to the Rayleigh-Taylor instability [42] between two types of fluids (water and air) with different densities [15; 43]. The spaces between the icicles were different, and the icicles received different quantities of droplets.