Montpelier examiner., 1912-02-02
THE GENERATION AND APPLI-
CATION OF ELECTRIC POWER
BY Arthur JOBsoN

TO arrive at a general rule for conf
putting the amount of power which
may be obtained from u given guam
tity of water under given head let
us imagine vertical pipe or penstock
500 feet in length having cross sec
tional area inside of one square foot
This pipe would then contain 500
cubic feet of water. The weight of a
cubic foot of water is about 82 4
pounds. Therefore the weight OF the
water in the pipe would be abont 3D.
200 pounds which would be the pres
sure in pounds per square foot at the
bottom of the pipe. If we assume
that the water in the pipe is flowing
ut the rate of one foot per second it
will be carrying one second foot of
water. Since this column of water
is assumed to be moving at the rate
of one foot per second, and as it exerts
u force of 81. 200 pounds at the lower
end, evidently it can do $1,000 foot
pounds of work in one second. If We
assume that the water is moving with
a velocity of two feet per second tthus
carrying two second feet it can do
twice as much work per second, or if
1t is moving with velocity of three
feet per second it can do three times
as much work, and so on, negleeting
the loss of head in the pipe for the
higher velocities. III the one second
foot of water can exert 81. 200 foot
pounds of work per second when pro-
perly utilized, it would be generating
56.7 III. p, which is the greatest pos
sible amount of power that can be
obtained from one second foot of
water under head 500 feet. 1.-THE
56.7 HI. p. is obtained by dividing 3D.
200 by $50, the number of foot-pounds
per second in each horsepower.) Sup
pose the pipe had cross-sectional
area of four square feet. Evidently
the pressure at the lower end would
be four times that given or ia, 800
pounds. III the water had mean ve-
locity of one foot per second the dis
charge would be four second feet,
and under these conditions the
amount of work which could be done
would be l24, 900 foot-pounds per Sec
ond, and hence four time the power
would be developed.
A general rule for computing the
i maximum amount of power which
can be obtained for a given quantity
of water under given head is as fol-
lows: Multiply the number of cubic
feet per second by 82.4. The product
will be the number of pounds of water
flowing per second. Multiply this
product by the vertical drop or head
In feet. Divide the result by $50.
The quotient will be the maximum
horsepower available. As an example
suppose there are 20 second feet of
water available for power purposes
under head of 800 feet. Multiply
ing 20 by 82.4 we obtain l,24s. Null
tiply 1,24S by 800 and we obtain 9as,-
400. Divide 998,400 by $50. The
quotient is 1876 in round numbers.
l.si5 would then be the greatest guam
tity of H. p. available. 1t would be
impossible to get more power than
this without creating energy. In fact
in actual practice the amount of
power obtained at the shaft of the
water wheel would be less than this
due to the loss of power by friction
In the water wheel and pipe line, and
the waste of water as it is being dis
charged onto the wheel. Ordinarily
we might expect, in a first class equip
ment, to obtain from the water wheel
shaft about 80 per cent of total quan.
tity OF power In the water, say ], 800
II, p. out OF the 1915 theorectical
horsepower.
! Where watar powsp 10 usad so'