Page 595 - Book Hosokawa Nanoparticle Technology Handbook

35 AC OVERHEAD TRANSMISSION LINE AUDIBLE-NOISE REDUCTION APPLICATIONS

Hydrophobicity Hydrophilicity
L
Smooth surface S SL

r t imes Tr ue surface area
Apparent surface area
Rough surface
f
f

Figure 35.3
Contact angle.

solid–liquid boundary. When the surface has become 3. Preparation of test power lines
rough and the surface area has become large, the
apparent contact angle is given by Wenzel’s equa- As is shown in Table 35.1, the test power lines used in
f
tion given by equation (35.2) below, and the contact the experiments have nine types of wetting property
angle becomes still larger on a hydrophobic surface with the contact angle being in the range from 0.3 to
causing the water droplet to have a spherical shape, 156.5º. In the case of a twisted wires structure in
whereas the contact angle becomes still smaller on a which aluminum alloy strands are bundled together,
hydrophilic surface causing the water droplet to there is some restriction on the methods of improving
spread in the lateral direction. Here, r is the surface- the surface because the wires are very long being more
area magnification factor. than a few hundred meters in length. Therefore, in the
present study, we attempted three types of methods
SL cos (35.1) using which it is possible to realize uniform surface
S
L improvement on the aluminum surface in open air.
To begin with, a simple method is that of coating the
r ( ) wires with a paint. Depending on the type of paint, it
cos S SL r cos (35.2) is possible to obtain different types of wetting proper-
L ties, and it is also possible to easily apply this method
f
on power lines that have already been installed on tow-
Further, in recent years, practical application of super- ers. However, in an environment in which the paint on
hydrophobic or super-hydrophilic surfaces is being the power lines is continuously exposed to strong
made for the purpose of preventing adhesion of ice or wind, rain, and sunlight, and in which there is a very
snow or for dirt resistance in the exteriors of build- severe difference between hot and cold weathers, the
ings. A super-hydrophobic surface has a remarkably life of the painted covering film is much shorter than
large effect of repelling water, and water droplets roll that of the power lines, and hence is not considered to
off easily from such a surface. On the other hand, a be realistic, except in special cases.
super-hydrophilic surface has an extremely large The next method of improving the surface proper-
effect of receptivity to water adhesion, and any water ties is the use of blasting. Sandblasting is actually
dropped on such a surface spreads very easily. As a being used, and its purpose is to roughen the power
guideline, the contact angle of super-hydrophobicity line surface, which is glossy in order to blend with the
is more than 150 , and the contact angle of super- environment by suppressing reflection of sun’s rays. In
hydrophilicity is about a few degrees. addition, using the blasting process, depending on its
In this report, we investigate surface improvement conditions, it is possible to implant a part of the blast-
methods that can be applied even to power line sur- ing material into the surface of the power line, and as
faces that are aluminum surfaces, prepare various a result, a wetting property that cannot be obtained by
power lines having a variety of wetting property char- aluminum alone can be obtained. The blasting process
acteristics from super-hydrophobicity to super- can be realized easily as one of the processes in the
hydrophilicity, and from experiments simulating manufacture of power lines.
transmission lines under rain, we clarify the relation- Finally, thermal spraying is a method of surface
ship between the wetting property of power lines and improvement by spraying a material in the molten state
audible noise. and at a high temperature onto the surface of the power

567