Biomedical Engineering Reference
In-Depth Information
refract sunlight to produce rainbows. As human utilization of water increases, so is the
amount of water in the cycle: more evaporation or release into the atmosphere and
more precipitation on land.
Water runoff often collects over watersheds flowing into rivers. Some of water is diverted
to irrigation for agriculture. Rivers and seas offer opportunity for travel and commerce. Over
time, water carries soil and deposits at shorelines, extending land surface. Through erosion,
runoff shapes the environment creating river valleys and deltas which provide rich soil and
level ground for the establishment of population centers. A flood occurs when an area of
land, usually low-lying, is covered with water. It is when a river overflows its banks or flood
from the sea. A drought is an extended period of months or years when a region notes a defi-
ciency in its water supply. This occurs when a region receives consistently below average
precipitation.
Example 15-2. Evaporation from Ocean at 398 Eg/year is due to absorption energy from
sunlight. Assume an average water temperature of 290 K, compute the energy released by
Ocean due to the evaporation of water into the atmosphere.
Solution.From
Table 15.2
,wefind:H
L
¼
70.7 kJ/kg and H
V
¼
2532 kJ/kg at 290 K.
Thus, the latent heat loss of evaporation:
H
ev
¼
H
V
H
L
¼
2461 kJ/kg. This translates
D
10
15
kJ/year
10
20
kJ/year.
to the energy release from the ocean of 2461
398
¼
9.80
9:80 10
20
365 24 3600
10
13
kW
It is equivalent to
kW
¼
3.11
¼
31.1 PW.
15.3.2. Utilization of Hydro Energy
The sustainable level of water on the land surface is a result of the solar energy exerted on
earth's surface. As depicted in
Fig. 15.5
, evaporation of water vapor from ocean is due to the
thermal energy provided by the Sun. Some of the condensation is carried over land, by wind
(advection). Again, wind is generated by the solar energy. Sunlight warms up regions of
atmosphere where water vapor is denser, causing a pressure differential. Wind is generated
because of the rotation of planet Earth as well as the pressure differentials. Precipitation falls
far inland, collecting together forming streams and rivers or waterways. The water flowing in
the river can be employed to generate electricity as depicted by
Fig. 15.6
. Worldwide, an
installed capacity of 777 GW supplied 2998 TWh of hydroelectricity in 2006, which repre-
sented a significant amount of renewable energy.
Hydropower has been used since ancient times to grind flour and perform other tasks.
In the mid-1770s, a French engineer Bernard Forest de B´lidor published Architecture
Hydraulique which described vertical- and horizontal-axis hydraulic machines. By the late
nineteenth century, the electrical generator was developed and could now be coupled with
hydraulics. In 1878, the world's first house powered with hydroelectricity was Cragside in
Northumberland, England. The old Schoelkopf Power Station No. 1 near Niagara Falls in
the U.S. side began to produce electricity in 1881. The first Edison hydroelectric power
plant
d
the Vulcan Street Plant
d
began operating September 30, 1882, in Appleton, Wisconsin,
with an output of about 12.5 kW. By 1886, there were about 45 hydroelectric power plants in
the U.S. and Canada. By 1889, there were 200 in the U.S. The development of hydropower was
rapid as the source of energy, water flowing through the waterway, never ends.
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