Environmental Engineering Reference
In-Depth Information
(3) The surface of the sail starts from the axis at a distance
of about 1/4 of the sail length, so the surface is 3/4 of the
sail length.
(4) The cross-section of the sail profile is not a straight line,
but bent at a point, which is 1/4 or 1/6 from the fore edge
and the fold is so strong that it is 3 to 4% of the chord of the
profile, especially at the tip of the sail, however, near the axis
it can be straight.
(5) The bevel angle is calculated from the profile chord, not
from the large sail surface, nor from the small sail surface.
It is 10 degrees at the sail tip and increases regularly so
it is 15 degrees at 2/3 of the distance from the axis and
20 degrees 1/3 from the axis and would be 25 degrees at
the axis.
(6) The mill should be arranged so that the tip of the sail runs
with a velocity factor of 2.4 the velocity of the incoming
wind, out of which it is desirable to extract the greatest
possible power (it will most commonly be near to 6 m/s or
maybe only 5 m/s).
(7) The work that such a mill produces can be calculated as
the research shows, by the fact that there is 60 g/m
2
sail
surface at a wind velocity of 1 m/s. The work will be a factor
60 of the total sail area in square metres multiplied by the
wind velocity cubed and will be expressed in gram-metres.
By dividing this number with 1 000 the value in kilogram-
metre per second will be determined. Divided again by 75
will give the answer in horse power.
Example:
If there are four sails, each of length 8 m and width 2 m,
and the power at wind velocity of 6 m/s is to be determined, then
first the tip velocity should be calculated, which will be 6 × 2.4 =
14.4 m/s. The circumference of the circle made by the wing tips
will
be about 50 m, so this mill will make (14.4 × 60)/50 = 17.3 turns/
min. Its sail surface will be 4 × 6 × 2 = 48 m
2
, and its power with the
aforementioned wind velocity will be 60 × 48 × 6
3
= 622080 g-m =
622 kg-m = 8.3 hp
.
After publishing his research report “Forsøgsmøllen I og II” (
The
Research Mill I and II
) in 1900, la Cour initiated a contest urging
millwrights to build the ideal mill. Some of them became very angry
as they were convinced they were already doing that! Millwright Chr.
Sørensen was especially angry, because his attractive conical rotor
Search WWH ::
Custom Search