Filed under: Water Power | Tags: Impulse Water Wheel, Tangential Water Wheel, Water Power
The modern impulse, or tangential wheel (so called because the driving
stream of water strikes the wheel at a tangent) is best adapted to
situations where the amount of water is limited, and the head is
large. Thus, a mountain brook supplying only seven cubic feet of water
a minute–a stream less than two-and-a-half inches deep flowing over a
weir with an opening three inches wide–would develop two actual
horsepower, under a head of 200 feet–not an unusual head to be found
in the hill country. Under a head of one thousand feet, a stream
furnishing 352.6 cubic feet of water a minute would develop 534.01
horsepower at the nozzle.
Ordinarily these wheels are not used under heads of less than 20 feet.
The Efficient Water Wheel
A wheel of this type, six feet in diameter, would develop six
horsepower, with 188 cubic feet of water a minute and 20-foot head.
The great majority of impulse wheels are used under heads of 100 feet
and over. In this country the greatest head in use is slightly over
2,100 feet, although in Switzerland there is one plant utilizing a
head of over 5,000 feet.
Efficient Modern Adaptations of the Archaic Undershot and Overshot Water Wheels
The old-fashioned impulse wheels were inefficient because of the fact
that their buckets were not constructed scientifically, and much of
the force of the water was lost at the moment of impact. The impulse
wheel of to-day, however, has buckets which so completely absorb the
momentum of water issuing from a nozzle, that the water falls into the
tailrace with practically no velocity. When it is remembered that the
nozzle pressure under a 2,250-foot head is nearly 1,000 pounds to the
square inch, and that water issues from this nozzle with a velocity of
23,000 feet a minute, the scientific precision of this type of bucket
can be appreciated.
A typical bucket for such a wheel is shaped like an open clam shell,
the central line which cuts the stream of water into halves being
ground to a sharp edge. The curves which absorb the momentum of the
water are figured mathematically and in practice become polished like
mirrors. So great is the eroding action of water, under great
heads–especially when it contains sand or silt–that it is
occasionally necessary to replace these buckets. For this reason the
larger wheels consist merely of a spider of iron or steel, with each
bucket bolted separately to its circumference, so that it can be
removed and replaced easily. Usually only one nozzle is provided; but
in order to use this wheel under low heads–down to 10 feet–a number
of nozzles are used, sometimes five, where the water supply is
plentiful.
The wheel is keyed to a horizontal shaft running in babbited bearings,
and this same shaft is used for driving the generator, either by
direct connection, or by means of pulleys and a belt. The wheel may be
mounted on a home-made timber base, or on an iron frame. It takes up
very little room, especially when it is so set that the nozzle can be
mounted under the flooring. The wheel itself is enclosed, above the
floor, in a wooden box, or a casing made of cast or sheet iron, which
should be water-tight.
Since these wheels are usually operated under great heads, the problem
of regulating their water supply requires special consideration. A
gate is always provided at the upper, or intake end, where the water
pipe leaves the flume. Since the pressure reaches 1,000 pounds the
square inch and more, there would be danger of bursting the pipe if
the water were suddenly shut off at the nozzle itself. For this reason
it is necessary to use a needle valve, similar to that in an ordinary
garden hose nozzle; and by such a valve the amount of water may be
regulated to a nicety. Where the head is so great that even such a
valve could not be used safely, provision is made to deflect the
nozzle. These wheels have a speed variation amounting to as much as 25
per cent from no-load to full load, in generating electricity, and
since the speed of the prime mover–the water wheel–is reflected
directly in the voltage or pressure of electricity delivered, the
wheel must be provided with some form of automatic governor. This
consists usually of two centrifugal balls, similar to those used in
governing steam engines; these are connected by means of gears to the
needle valve or the deflector.
As the demand for farm water-powers in our hill sections becomes more
general, the tangential type of water wheel will come into common use
for small plants. At present it is most familiar in the great
commercial installations of the Far West, working under enormous
heads. These wheels are to be had in the market ranging in size from
six inches to six feet and over. Wheels ranging in size from six
inches to twenty-four inches are called water motors, and are to be
had in the market, new, for $300 for the smallest size, and $2750 for
the largest. Above three feet in diameter, the list prices will run
from $2000 for a 3-foot wheel to $8000 for a 6-foot wheel. Where one has
a surplus of water, it is possible to install a multiple nozzle wheel,
under heads of from 10 to 100 feet, the cost for 18-inch wheels of
this pattern running from $1500 to $1800 list, and for 24-inch wheels
from $2000 to $2500. A 24-inch wheel, with a 10-foot head would give
1.19 horsepower, enough for lighting the home, and using an electric
iron. Under a 100-foot head this same wheel would provide 25.9
horsepower, to meet the requirements of a bigger-than-average farm
plant.
Filed under: Water Power | Tags: Water Power, water powered farm, water wheels
In general, there are two types of water wheels, the _impulse_ wheel
and the _reaction_ wheel. Both are called turbines, although the name
belongs, more properly, to the reaction wheel alone.
Impulse wheels derive their power from the _momentum_ of falling
water. Reaction wheels derive their power from the _momentum and
pressure_ of falling water. The old-fashioned _undershot_, _overshot_,
and _breast_ wheels are familiar to all as examples of impulse
wheels. Water wheels of this class revolve in the air, with the energy
of the water exerted on one face of their buckets. On the other hand,
reaction wheels are enclosed in water-tight cases, either of metal or
of wood, and the buckets are entirely surrounded by water.
The old-fashioned undershot, overshot, and breast wheels were not very
efficient; they wasted about 75 per cent of the power applied to them.
A modern impulse wheel, on the other hand, operates at an efficiency
of 80 per cent and over. The loss is mainly through friction and
leakage, and cannot be eliminated altogether. The modern reaction
wheel, called the _turbine_, attains an equal efficiency. Individual
conditions govern the type of wheel to be selected.
The Topics we will cover in the upcoming days include:
Different types of water wheels–The impulse and reaction
wheels–The impulse wheel adapted to high heads and small amount of
water–Pipe lines–Table of resistance in pipes–Advantages and
disadvantages of the impulse wheel–Other forms of impulse
wheels–The reaction turbine, suited to low heads and large
quantity of water–Its advantages and limitations–Developing a
water-power project: the dam; the race; the flume; the penstock;
and the tailrace–Water rights for the farmer.
Filed under: Water Power | Tags: measure water power, water, water powered farm, water wheels
Let us take still another problem which the prospector may be called
on to solve: _A man finds that he can conveniently get a fall of 27
feet. He desires 20 actual horsepower. What quantity of water will be
necessary, and what capacity wheel?_
Twenty actual horsepower will be 20 x 4/3 = 26.67 theoretical
horsepower. Formula:
33,000 x Hp. required
(D) Cubic feet per minute = ———————
(Head in feet x 62.5)
Substituting values, then, we have:
Cu. ft. per minute =
33,000 x 26.67
————– = 521.5 cubic feet a minute.
27 x 62.5
A head of 27 feet would give this stream a velocity of 41.7 feet a
second, and, from formula (B) we find that the capacity of the wheel
The Efficient Water Wheel
should be 30 square inches.
It is well to remember that the square inches of wheel capacity does
not refer to the size of pipe conveying water from the head to the
wheel, but merely to the actual nozzle capacity provided by the wheel
itself. In small installations of low head, such as above a penstock
at least six times the nozzle capacity should be used, to avoid losing
effective head from friction. Thus, with a nozzle of 30 square inches,
the penstock or pipe should be 180 square inches, or nearly 14 inches
square inside measurement. A larger penstock would be still better.
Tommorrow THE WATER WHEEL AND HOW TO INSTALL IT
Filed under: Water Power | Tags: measure water power, water head, water wheels
Let us attack the problem of water-power in another way. _A farmer
wishes to install a water wheel that will deliver 10 horsepower on the
shaft, and he finds his stream delivers 400 cubic feet of water a
minute. How many feet fall is required?_ Formula:
33,000 x horsepower required
(C) Head in feet = ——————————
Cu. Ft. per minute x 62.5
Since a theoretical horsepower is only 75 per cent efficient, he would
require 10 x 4/3 = 13.33 theoretical horsepower of water, in this
instance. Substituting the values of the problem in the formula, we
have:
33,000 x 13.33
Answer: Head = —————- = 17.6 feet fall required.
400 x 62.5
_What capacity of wheel would this prospect (400 cubic feet of water a
minute falling 17.6 feet, and developing 13.33 horsepower) require?_
By referring to the table of velocities, we find that the velocity for
17.5 feet head (nearly) is 33.6 feet a second. Four hundred feet of
water a minute is 400/60 = 6.67 cu. ft. a second. Substituting these
values, in formula (B) then, we have:
Answer: Capacity of wheel =
144 x 6.67
———- = 28.6 square inches of water.
33.6
Filed under: Water Power | Tags: measure water power, water powered farm, water wheels
Water wheels are not rated by horsepower by manufacturers, because the
same wheel might develop one horsepower or one hundred horsepower, or
even a thousand horsepower, according to the conditions under which
it is used. With a given supply of water, the head, in feet,
determines the size of wheel necessary. The farther a stream of water
falls, the smaller the pipe necessary to carry a given number of
gallons past a given point in a given time.
A small wheel, under 10 x 13.5 ft. head, would give the same power
Small Water Wheel
with the above 376 cubic feet of water a minute, as a large wheel
would with 10 x 376 cubic feet, under a 13.5 foot head.
This is due to the _acceleration of gravity_ on falling bodies. A
rifle bullet shot into the air with a muzzle velocity of 3,000 feet a
second begins to diminish its speed instantly on leaving the muzzle,
and continues to diminish in speed at the fixed rate of 32.16 feet a
second, until it finally comes to a stop, and starts to descend. Then,
again, its speed accelerates at the rate of 32.16 feet a second, until
on striking the earth it has attained the velocity at which it left
the muzzle of the rifle, less loss due to friction.
The acceleration of gravity affects falling water in the same manner
as it affects a falling bullet. At any one second, during its course
of fall, it is traveling at a rate 32.16 feet a second in excess of
its speed the previous second.
In figuring the size wheel necessary under given conditions or to
determine the power of water with a given nozzle opening, it is
necessary to take this into account. The table on page 51 gives
velocity per second of falling water, ignoring the friction of the
pipe, in heads from 5 to 1000 feet.
The scientific formula from which the table is computed is expressed
as follows, for those of a mathematical turn of mind:
Velocity (ft. per sec.) = sqrt(2gh); or, velocity is equal to the
square root of the product (g = 32.16,–times head in feet, multiplied
by 2).
SPOUTING VELOCITY OF WATER, IN FEET PER SECOND, IN HEADS
OF FROM 5 TO 1,000 FEET
Head Velocity
5 17.9
The Efficient Water Wheel
6 19.7
7 21.2
8 22.7
9 24.1
10 25.4
11 26.6
11.5 27.2
12 27.8
12.5 28.4
13 28.9
13.5 29.5
14 30.0
14.5 30.5
15 31.3
15.5 31.6
16 32.1
16.5 32.6
17 33.1
17.5 33.6
18 34.0
18.5 34.5
19 35.0
19.5 35.4
20 35.9
20.5 36.3
21 36.8
21.5 37.2
22 37.6
22.5 38.1
23 38.5
23.5 38.9
24 39.3
24.5 39.7
25 40.1
26 40.9
27 41.7
28 42.5
29 43.2
30 43.9
31 44.7
32 45.4
33 46.1
34 46.7
35 47.4
36 48.1
37 48.8
38 49.5
39 50.1
40 50.7
41 51.3
42 52.0
43 52.6
44 53.2
45 53.8
46 54.4
47 55.0
48 55.6
49 56.2
50 56.7
55 59.5
60 62.1
65 64.7
70 67.1
75 69.5
80 71.8
85 74.0
90 76.1
95 78.2
100 80.3
200 114.0
300 139.0
400 160.0
500 179.0
1000 254.0
_In the above example, we found that 376 cubic feet of water a minute,
under 13.5 feet head, would deliver 7.2 actual horsepower. Question:
What size wheel would it be necessary to install under such
conditions?_
By referring to the table of velocity above, (or by using the
formula), we find that water under a head of 13.5 feet, has a spouting
velocity of 29.5 feet a second. This means that a solid stream of
water 29.5 feet long would pass through the wheel in one second. _What
should be the diameter of such a stream, to make its cubical contents
376 cubic feet a minute or 376/60 = 6.27 cubic feet a second?_ The
following formula should be used to determine this:
144 x cu. ft. per second
(B) Sq. Inches of wheel = ————————–
Velocity in ft. per sec.
Substituting values, in the above instance, we have:
Answer: Sq. Inches of wheel =
144 x 6.27 (Cu. Ft. Sec.)
————————— = 30.6 sq. in.
29.5 (Vel. in feet.)
That is, a wheel capable of using 30.6 square inches of water would
meet these conditions.
By one of the above simple methods, the problem of _Quantity_ can
easily be determined. The next problem is to determine what _Head_ can
be obtained. _Head_ is the distance in feet the water may be made to
fall, from the Source of Supply, to the water wheel itself. The power
of water is directly proportional to _head_, just as it is directly
proportional to _quantity_. Thus the typical weir measured above was
30 inches wide and 6-1/4 deep, giving 189 cubic feet of water a
minute–_Quantity._ Since such a stream is of common occurrence on
thousands of farms, let us analyze briefly its possibilities for
power: One hundred and eighty-nine cubic feet of water weighs 189 x
62.5 pounds = 11,812.5 pounds. Drop this weight one foot, and we have
11,812.5 foot-pounds. Drop it 3 feet and we have 11,812 x 3 =
35,437.5 foot-pounds. Since 33,000 foot-pounds exerted in one minute
is one horsepower, we have here a little more than one horsepower. For
simplicity let us call it a horsepower.
Now, since the work to be had from this water varies directly with
_quantity_ and _head_, it is obvious that a stream _one-half_ as big
Water Wheel for Power
falling _twice_ as far, would still give one horsepower at the wheel;
or, a stream of 189 cubic feet a minute falling _ten times_ as far, 30
feet, would give _ten times_ the power, or _ten_ horsepower; a stream
falling _one hundred times_ as far would give _one hundred_
horsepower. Thus small quantities of water falling great distances, or
large quantities of water falling small distances may accomplish the
same results. From this it will be seen, that the simple formula for
determining the theoretical horsepower of any stream, in which
Quantity and Head are known, is as follows:
Cu. Ft.
per Feet
minute x head x 62.5
(A) Theoretical Horsepower = ———————-
33,000
_As an example, let us say that we have a stream whose weir
measurement shows it capable of delivering 376 cubic feet a minute,
with a head (determined by survey) of 13 feet 6 inches. What is the
horsepower of this stream?_
Answer:
Cu. ft. p. m. head pounds
376 x 13.5 x 62.5
H.P. = —————————– = 9.614 horsepower
33,000
This is _theoretical horsepower_. To determine the _actual_ horsepower
that can be counted on, in practice, it is customary, with small water
wheels, to figure 25 per cent loss through friction, etc. In this
instance, the actual horsepower would then be 7.2.
Filed under: Water Power | Tags: measure a stream, measure water power, water wheels
Weirs are for use in small streams. For larger streams, where the
construction of a weir would be difficult, the U. S. Geological Survey
engineers recommend the following simple method:
Measuring Larger Streams
Choose a place where the channel is straight for 100 or 200 feet, and
has a nearly constant depth and width; lay off on the bank a line 50
or 100 feet in length. Throw small chips into the stream, and measure
the time in seconds they take to travel the distance laid off on the
bank. This gives the surface velocity of the water. Multiply the
average of several such tests by 0.80, which will give very nearly the
mean velocity. Then it is necessary to find the cross-section of the
flowing water (its average depth multiplied by width), and this
number, in square feet, multiplied by the velocity in feet per second,
will give the number of cubic feet the stream is delivering each
second. Multiplied by 60 gives cubic feet a minute.
Filed under: Water Power | Tags: measure water power, water powered farm, water wheels, weir
Since a steady flow of water, and a constant head, bring about this
ideal condition in the water wheel, the first problem that faces the
farmer prospector is to determine the amount of water which his stream
is capable of delivering. This is always measured, for convenience,
in _cubic feet per minute_. (A cubic foot of water weighs 62.5 pounds,
and contains 7-1/2 gallons.) This measurement is obtained in several
ways, among which probably the use of a weir is the simplest and most
accurate, for small streams.
A weir is, in effect, merely a temporary dam set across the stream in
such a manner as to form a small pond; and to enable one to measure
the water escaping from this pond.
It may be likened to the overflow pipe of a horse trough which is
being fed from a spring. To measure the flow of water from such a
spring, all that is necessary is to measure the water escaping through
the overflow when the water in the trough has attained a permanent
level.
[Illustration: Detail of home-made weir]
[Illustration: Cross-section of weir]
The diagrams show the cross-section and detail of a typical weir,
which can be put together in a few minutes with the aid of a saw and
hammer. The cross-section shows that the lower edge of the slot
through which the water of the temporary pond is made to escape, is
cut on a bevel, with its sharp edge upstream. The wing on each side of
the opening is for the purpose of preventing the stream from narrowing
as it flows through the opening, and thus upsetting the calculations.
This weir should be set directly across the flow of the stream,
perfectly level, and upright. It should be so imbedded in the banks,
and in the bottom of the stream, that no water can escape, except
through the opening cut for that purpose. It will require a little
experimenting with a rough model to determine just how wide and how
deep this opening should be. It should be large enough to prevent
water flowing over the top of the board; and it should be small
enough to cause a still-water pond to form for several feet behind the
weir. Keep in mind the idea of the overflowing water trough when
building your weir. The stream, running down from a higher level
behind, should be emptying into a still-water pond, which in turn
should be emptying itself through the aperture in the board at the
same rate as the stream is keeping the pond full.
Your weir should be fashioned with the idea of some permanency so that
a number of measurements may be taken, extending over a period of
time–thus enabling the prospector to make a reliable estimate not
only of the amount of water flowing at any one time, but of its
fluctuations.
Under expert supervision, this simple weir is an exact
contrivance–exact enough, in fact, for the finest calculations
required in engineering work. To find out how many cubic feet of water
the stream is delivering at any moment, all that is necessary is to
measure its depth where it flows through the opening. There are
instruments, like the hook-gauge, which are designed to measure this
depth with accuracy up to one-thousandth of an inch. An ordinary foot
rule, or a folding rule, will give results sufficiently accurate for
the water prospector in this instance. The depth should be measured
not at the opening itself, but a short distance back of the opening,
where the water is setting at a dead level and is moving very slowly.
With this weir, every square inch of water flowing through the opening
indicates roughly one cubic foot of water a minute. Thus if the
opening is 10 inches wide and the water flowing through it is 5 inches
deep, the number of cubic feet a minute the stream is delivering is 10
x 5 = 50 square inches = 50 cubic feet a minute. This is a very small
stream; yet, if it could be made to fall through a water wheel 10 feet
below a pond or reservoir, it would exert a continuous pressure of
30,000 pounds per minute on the blades of the wheel–nearly one
theoretical horsepower.
This estimate of one cubic foot to each square inch is a very rough
approximation. Engineers have developed many complicated formulas for
determining the flow of water through weirs, taking into account fine
variations that the farm prospector need not heed. The so-called
Francis formula, developed by a long series of actual experiments at
Lowell, Mass., in 1852 by Mr. James B. Francis, with weirs 10 feet
long and 5 feet 2 inches high, is standard for these calculations and
is expressed (for those who desire to use it for special purposes) as
follows:
Q = 3.33 L H^(3/2) or, Q = 3.33 L H sqrt(H),
in which Q means _quantity_ of water in cubic feet per second, L is
length of opening, in feet; and H is height of opening in feet.
The following table is figured according to the Francis formula, and
gives the discharge in cubic feet per minute, for openings one inch
wide:
TABLE OF WEIRS
Inches 0 1/4 1/2 3/4
1 0.403 0.563 0.740 0.966
2 1.141 1.360 1.593 1.838
3 2.094 2.361 2.639 2.927
4 3.225 3.531 3.848 4.173
5 4.506 4.849 5.200 5.558
6 5.925 6.298 6.681 7.071
7 7.465 7.869 8.280 8.697
8 9.121 9.552 9.990 10.427
9 10.884 11.340 11.804 12.272
10 12.747 13.228 13.716 14.208
11 14.707 15.211 15.721 16.236
12 16.757 17.283 17.816 18.352
13 18.895 19.445 19.996 20.558
14 21.116 21.684 22.258 22.835
15 23.418 24.007 24.600 25.195
16 25.800 26.406 27.019 27.634
17 28.256 28.881 29.512 30.145
18 30.785 31.429 32.075 32.733
Thus, let us say, our weir has an opening 30 inches wide, and the
water overflows through the opening at a uniform depth of 6-1/4
inches, when measured a few inches behind the board at a point before
the overflow curve begins. Run down the first column on the left to
“6″, and cross over to the second column to the right, headed “1/4″.
This gives the number of cubic feet per minute for this depth one inch
wide, as 6.298. Since the weir is 30 inches wide, multiply 6.298 x 30
= 188.94–or, say, 189 cubic feet per minute.
Once the weir is set, it is the work of but a moment to find out the
quantity of water a stream is delivering, simply by referring to the
above table.
Filed under: Water Power | Tags: measure water power, water powered farm, water wheels
The Efficient Water Wheel
The farmer, prospecting on his land for water-power, locates a spot on
a stream which he calls Supply; and another spot a few feet down hill
near the same stream, which he calls Power. Every gallon of water that
falls between these two points, and is made to escape through the
revolving blades of a water wheel is capable of work in terms of
foot-pounds–an amount of work that is directly proportional to the
_quantity_ of water, and to the _distance_ in feet which it falls to
reach the wheel–_pounds_ and _feet_.
_The Efficient Water Wheel_
And it is a very efficient form of work, too. In fact it is one of the
most efficient forms of mechanical energy known–and one of the
easiest controlled. A modern water wheel uses 85 per cent of the total
capacity for work imparted to falling water by gravity, and delivers
it as rotary motion. Compare this water wheel efficiency with other
forms of mechanical power in common use: Whereas a water wheel uses 85
per cent of the energy of its water supply, and wastes only 15 per
cent, a gasoline engine reverses the table, and delivers only 15 per
cent of the energy in gasoline and wastes 85 per cent–and it is
rather a high-class gasoline engine that can deliver even 15 per cent;
a steam engine, on the other hand, uses about 17 per cent of the
energy in the coal under its boilers and passes the rest up the
chimney as waste heat and smoke.
There is still another advantage possessed by water-power over its two
rivals, steam and gas: It gives the most even flow of power. A gas
engine “kicks” a wheel round in a circle, by means of successive
explosions in its cylinders. A reciprocating steam engine “kicks” a
wheel round in a circle by means of steam expanding first in one
direction, then in another. A water wheel, on the other hand, is made
to revolve by means of the pressure of water–by the constant force of
gravity, itself–weight. Weight is something that does not vary from
minute to minute, or from one fraction of a second to another. It is
always the same. A square inch of water pressing on the blades of a
water wheel weights ten, twenty, a hundred pounds, according to the
height of the pipe conveying that water from the source of supply, to
the wheel. So long as this column of water is maintained at a fixed
height, the power it delivers to the wheel does not vary by so much as
the weight of a feather.
This property of falling water makes it the ideal power for generating
electricity. Electricity generated from mechanical power depends on
constant speed for steady pressure–since the electric current, when
analyzed, is merely a succession of pulsations through a wire, like
waves beating against a sea wall. Water-power delivers these waves at
a constant speed, so that electric lights made from water-power do not
flicker and jump like the flame of a lantern in a gusty wind. On the
other hand, to accomplish the same thing with steam or gasoline
requires an especially constructed engine.
Filed under: Water Power | Tags: electric power plants, measure water power, water powered farm
What is a horsepower?–How the Carthaginians manufactured
horsepower–All that goes up must come down–How the sun lifts
water up for us to use–Water the ideal power for generating
electricity–The weir–Table for estimating flow of streams, with a
weir–Another method of measuring–Figuring water horsepower–The
size of the wheel–What head is required–Quantity of water
necessary.
If a man were off in the woods and needed a horsepower of energy to
work for him, he could generate it by lifting 550 pounds of stone or
wood, or whatnot, one foot off the ground, and letting it fall back in
the space of one second. As a man possesses capacity for work equal to
one-fifth horsepower, it would take him five seconds to do the work of
lifting the weight up that the weight itself accomplished in falling
down. All that goes up must come down; and by a nice balance of
physical laws, a falling body hits the ground with precisely the same
force as is required to lift it to the height from which it falls.
The Carthaginians, and other ancients (who were deep in the woods as
regards mechanical knowledge) had their slaves carry huge stones to
the top of the city wall; and the stones were placed in convenient
positions to be tipped over on the heads of any besieging army that
happened along. Thus by concentrating the energy of many slaves in one
batch of stones, the warriors of that day were enabled to deliver
“horsepower” in one mass where it would do the most good. The farmer
who makes use of the energy of falling water to generate electricity
for light, heat, and power does the same thing–he makes use of the
capacity for work stored in water in being lifted to a certain height.
As in the case of the gasoline engine, which burns 14 pounds of air
for every pound of gasoline, the engineer of the water-power plant
does not have to concern himself with the question of how this
natural source of energy happened to be in a handy place for him to
make use of it.
The sun, shining on the ocean, and turning water into vapor by its
heat has already lifted it up for him. This vapor floating in the air
and blown about by winds, becomes chilled from one cause or another,
gives up its heat, turns back into water, and falls as rain. This
rain, falling on land five, ten, a hundred, a thousand, or ten
thousand feet above the sea level, begins to run back to the sea,
picking out the easiest road and cutting a channel that we call a
brook, a stream, or a river. Our farm lands are covered to an average
depth of about three feet a year with water, every gallon of which has
stored in it the energy expended by the heat of the sun in lifting it
to the height where it is found.
The farmer, prospecting on his land for water-power, locates a spot on
a stream which he calls Supply; and another spot a few feet down hill
near the same stream, which he calls Power. Every gallon of water that
falls between these two points, and is made to escape through the
revolving blades of a water wheel is capable of work in terms of
foot-pounds–an amount of work that is directly proportional to the
_quantity_ of water, and to the _distance_ in feet which it falls to
reach the wheel–_pounds_ and _feet_.
Next We will Look At the Efficient Water Wheel
