Water Power

Collier's New Encyclopedia (1921)

a general phrase applied to the various means by which the energy of moving water may be To make such a source of utilized. energy effectual, it is necessary and sufficient to have water falling from a higher to a lower level; in other words the water must have what is technically called a "head." Such conditions more or less favorable exist in all streams, though in many cases the fall is so slight and therefore the volicity of the water so small that practically no useful work can be obtained. In such cases, by the construction of dams or otherwise, the energy may be stored up as potential energy in a large mass of water to be transformed at will. Even where the stream is one which is directly available for performing useful work, it is usually advisable to collect the water in reservoirs, since the quantity of flow of most considerably with the streams varies co Even with such precautions the seasons. supply of water may be far from uniform, overflowing the dams in the wet season and hardly filling them in the dry weather. Given the available fall and the total quantity of water which flows in a given time, the potential energy which is lost by the prodis expresed in foot pounds uct of the mass in pounds multiplied by the height through which the water has formed into the kinetic energy of runfallen. This energy is mainly transning water, while part is transformed and sound. If the former portion could be wholly transformed into into heat useful work, the water would be brought to rest; but as this is never practically realized, we see that the available energy of a fall of water is much smaller than the total transformable energy. Of the various machines by which the necessary transformation is usefully effected, the most common are what are known as water wheels, in their several forms of turbines, undershot wheels, breast wheels and overshot wheels. The last three are very similar in construction, and are made to rotate round a horizontal axis by the action of the water on the floats which are fixed at equal intervals more or less radically round the circumference of the wheel. overshot wheel, which is cable to falls of from 12 to 60 feet, the In the appliwater is received in the bucket-shaped partitions in the circumference, and by its weight, aided in some measure by the initial impact, drives the wheel round, the upper part moving in the direction of the flow water. The water escapes below as each partition during the rotation of the wheel is turned face downward. The breast wheel acts very similarly, and is applicable to falls smaller than those for which the overshot wheel can be conveniently used. The upper circumference of the wheel is higher than the feeding channel of the water, which enters at a point usually a little above the center of the wheel. The undershot wheel is used where the momentum only of the current can be utilized, the impact of the water upon the floats forcing the wheel round. There is necessarily a considerable waste of power in the undershot wheel, which was to a certain extent remedied by Poncelet when he introduced curved instead of plane floats. The turbine or vortex wheel is usually horizontal, rotating round a vertical axis. In the original form of turbine, invented by Fourneyron in 1823, water was introduced from above into a central chamber, from which it radiated through curved radial chambers. From these it was projected on the curved floats of the wheel, which was forced round by the reaction of the escaping water. Though it is from rivers and streams that we derive all the water power which is profitably used, there is no doubt that in the tides we have a great and remarkably constant source of energy, if it could be utilized. Suggestions have not been wanting as to methods for utilizing this energy, but as yet nothing practical has resulted.