Wind turbine cooling technologies - Wind Power Generation and Wind Turbine Design - page 621

Then it gets cooled in the external radiator on top of the rear of the nacelle, and
fi nally runs back to the generator and the control converter to begin the next
cooling cycle.
At present, the cooling mediums commonly used in the liquid cooling system
are water and ethylene glycol aqueous solution. Comparing with water, ethylene
glycol aqueous solution has better anti-freeze property. Table 1 shows freezing
points of ethylene glycol aqueous solution in different densities. By adding a cer-
tain amount of stabilizers and preservatives, the minimum working temperature
can extend to -50°C, but keeps its heat transfer performance equivalent to that of
water [19].
Besides, in order to enhance the heat-exchange performance, the external heat
exchanger adopts an effective and compact plate-fi n structure, which is usually
made of the light metal, aluminum. The heat exchanger exposed to the external
environment is prone to be corroded, which will affect the durable, reliable opera-
tion of the heat exchanger. Therefore, necessary anti-corrosion treatments need to
be implemented, like coating the aluminum fl akes with anti-corrosive allyl resin
coverings and employing hydrophilic membranes on its outer surface. Having
been treated with this method, the acid rainproof of the aluminum fi ns and the anti-
salt corrosion property can be 5-6 times as large as those of the ordinary ones.
In the design of the heat exchanger, due to relatively large difference of the cooling
system operating loads in winter and summer, the summer operating mode is adopted
as the design condition, while the heat transfer effi ciency can be controlled through
a bypassing method in winter.
Comparing with the wind turbine adopting the air cooling method, the one
adopting liquid cooling system has a more compact structure. Although it increases
the cost of heat exchanger, cooling medium and corresponding laying of connecting
pipelines, it extremely enhances the cooling performance for the wind generating

Table 1: Freezing points of ethylene glycol aqueous
solution in different densities.

Density (%) Freezing point (°C)

0 0

5 − 2.0

10 − 4.3

20 − 9

30 − 17

40 − 26

50 − 38

60 − 50.1

70 − 48.5

80 − 41.8

85 − 36

90 − 26.8

100 − 13