Environmental Engineering Reference
In-Depth Information
daily food energy intake, a single small watermill would
have produced enough of it in a 10-h shift for about
3,500 people, a good-sized medieval town.
Unit capacities grew slowly. During the eighteenth
century, European waterwheels still averaged less than 4
kW and rarely exceeded 7.5 kW; heavy parts and poor
gearing led to low efficiencies. Larger outputs were
achieved by multiple installations and later also by build-
ing massive wheels. An exceptional Roman mill-line at
Barb
ยด
gal near Arles had 16 wheels with at least 1.5 kW
of useful capacity for a total of 24 kW (Sellin 1983). A
water-pumping installation on the Seine at Marly, built
between 1680 and 1688 to supply 1,400 fountains and
cascades at Versailles, had 14 large (10-m diameter)
wheels to drive over 200 pumps and raise about 150
m
3
/h of water 162 m high in three stages. The project
exploited a site with the overall potential of nearly 750
kW, but because of the wasteful transmission of rotary
motion via long reciprocating rods, the useful output
was only about 52 kW, not enough to supply water for
all the fountains (Brandstetter 2005). By the early 1830s,
Shaw's water works at Greenock on the Clyde near Glas-
gow consisted of 30 units, situated in two rows on a
steep slope and fed from a large reservoir to provide
about 1.5 MW with possible extension to 2.2 MW.
The largest waterwheels had diameters around 20 m
and capacities above 50 kW. The one at the lower end
of the Greenock falls had a diameter of 21.4 and a width
of 4 m. Burden wheel in Troy, New York, was 18.9 m
across and 6 m wide. In Cornwall a wheel with 13.7 m
diameter developed 52 kW (Woodall 1982). The largest
wheel ever built was Lady Isabella, belonging to Great
Laxey Mining Company on the Isle of Man (J. Reynolds
1970). This pitchback overshot machine had a diameter
of 21.9 m and a width of 1.85 m; its 48 spokes (9.75 m
long) were wooden, the axle and diagonal drawing rods
were wrought iron, the bearings were cast iron resting
on two large oak beams, the total weight was about 80 t,
and the wheel had 2.5 rpm. Streams on the slope above
the wheel were channeled into the collecting tanks, and
water was piped into the base of the masonry tower
and ascended into a wooden flume. The power was
transmitted to the pump rod at the bottom of a 451-m-
deep lead-zinc mine shaft by the main-axle crank and
180 m of timber connecting rods. The theoretical peak
was about 427 kW, and normal operation delivered
about 200 kW of useful power. Built in 1854, the wheel
worked until 1926, and it was restored after 1965.
There were also floating wheels set up on anchored
vessels. In 537
C
.
E
., Belisarius used them to grind grain
in a Rome besieged by Goths, and many floating mills
remained in Europe until the eighteenth century. Tidal
mills were first documented in Basra of the tenth century,
and during the Middle Ages they were built in England,
the Netherlands, the Atlantic coast of the Iberian penin-
sula, and above all, in Brittany. Installations in North
America and the Caribbean came later (Minchinton and
Meigs 1980). Most of these mills worked only with the
ebbing tide, but larger ones had reservoirs extending
the operation to 16 h instead of the usual 8-10 h/day.
Tide-driven undershots, including a large 9.75-m wheel,
also powered the pumps that supplied London's water.
The first radical improvement of water-driven prime
movers came only with the development of the water
turbine. First, in 1832, came Benoit Fourneyron's reac-
tion turbine (with radial outward flow), which was built
to run forge hammers at Fraisans. Under the head of
1.3 m and with a rotor diameter of 2.4 m, it delivered
38 kW. By 1837 two of Fourneyron's machines for the
Saint Blaisien spinning mill worked under high heads of
