Environmental Engineering Reference
In-Depth Information
often dangerous task of adjusting canvas to different
wind speeds, and cast metal gearings. The Dutch, the
world's leading windmill operators, adopted fantails only
in the early nineteenth century, but they had the first ef-
ficient blade designs once they added a canted leading
edge to previously flat blades (c. 1600). True airfoils,
aerodynamically contoured blades with thick leading
edges, were introduced in England only toward the end
of the nineteenth century.
The first drainage mills date from Holland after 1300,
but they became common only during the sixteenth cen-
tury. By 1650, the United Provinces of Netherlands had
at least 8,000 such machines, but the hollow-post wip-
molen turning big wooden wheels with scoops, and the
small mobile tjasker rotating Archimedean screws, had
to be superseded by efficient smock mills before the
country could begin large-scale reclamation of polders.
European windmills were also used in grinding and
crushing (chalk, sugarcane, mustard, cocoa), paper-
making, sawing, and metal working (Hill 1984). New
U.S. windmills appeared after the middle of the nine-
teenth century, with the westward expansion across the
Great Plains. They had many narrow blades or slats on
solid or sectional wheels, equipped with a centrifugal or
a side vane governor and independent rudders, placed
on top of lattice towers, and used to pump water for
households, cattle, or steam locomotives (fig. 7.7). These
windmills, barbed wire, and railroads were the iconic arti-
facts that helped to open up the Great Plains (T. L.
Baker 1985; A. M. Wilson 1999).
There is very little information on the energy output of
early windmills. The first experimental measurements
date from the 1750s, when John Smeaton matched the
power of a common Dutch mill with nine-meter sails
with the power produced by ten men or two horses
(Smeaton 1759). This calculation, based on measure-
ments with a small model, was corroborated by actual
performance in oilseed pressing: while the wind-powered
runners turned seven times a minute, two horses made
scarcely 3.5 turns in the same time. Forbes (1958) esti-
mated that a typical large eighteenth-century Dutch mill
of 30-m span, when equipped with improved sails and
turning in 8-9 m/s winds, could develop about 7.5 kW
at the windshaft. The best modern sails and gearings
could raise the output to as much as 15-22.5 kW. Mea-
surements at a preserved 1648 marsh mill that lifted
35 m
3
of water at 2 m/min in 8-9 m/s winds showed a
shaft power of about 30 kW but an actual output of just
11.6 kW, a transmission loss of 61%. This confirms Ran-
kine's (1859) comparison, in which he assumed useful
power of 2-8 hp (1.5-6 kW) for eighteenth-century
post windmills and 6-14 hp (4.5-10.4 kW) for tower
mills.
Wolff 's (1900) measurements indicate just 30 W for
U.S. wheels with a diameter of 2.5 m, and up to 1 kW
for large 7.6-m devices. Representative ranges would be
0.1-1 kW of useful power for the nineteenth-century
U.S. wheels, 1-2 kW for small post mills, 2-5 kW for
large post mills, 4-8 kW for common smock and tower
mills, and 8-12 kW for the largest nineteenth-century
devices. Typical medieval windmills were thus as power-
ful as contemporaneous waterwheels, but by the early
nineteenth century many hydraulic installations were four
to five times more powerful than even the largest wind-
mills. The importance of windmills peaked during the
nineteenth century. As many as 10,000 of them worked
after 1800 in England, 18,000 in 1895 in Germany, and
some 30,000 (100 MW) by 1900 in countries around
the North Sea (DeZeeuw 1978). Between 1860 and
1900 several million Halladays, Adamses, Buchanans,
