. A text book of physics, for the use of students of science and engineering . ot wheels. In boththese types, the attempt is toutilise the potential energy of thewater only. In under-shot wheelsthe wheel is furnished with blades, and the water is caused to impinge on these near the bottom of the wheel. The water entering the wheel must have considerable speed, and its kinetic energy is utilised. Water-wheels are seldom constructed now ; they waste a large amount of the available energy and are not suitable for developing large powers. Water-turbines.—The modern system of utilising the energy o
. A text book of physics, for the use of students of science and engineering . ot wheels. In boththese types, the attempt is toutilise the potential energy of thewater only. In under-shot wheelsthe wheel is furnished with blades, and the water is caused to impinge on these near the bottom of the wheel. The water entering the wheel must have considerable speed, and its kinetic energy is utilised. Water-wheels are seldom constructed now ; they waste a large amount of the available energy and are not suitable for developing large powers. Water-turbines.—The modern system of utilising the energy ofelevated water is by the employment of turbines. In these machinesthe water passes through a wheel furnished with blades. The actionconsists in causing the water to whirl before entering the wheel ; intins condition it possesses angular momentum, and the function ofthe wheel blades is i abstract the angular momentum and to dis-charge the water with no whirl. A couple will thus act on the wheel(p. 206), and will cause it to rotate, thus performing mechanical Fig. 315.—Over-shot water-wheel. XXI WATER TURBINES 293 In impulse turbines arrangements are made so as to convert thewhole of the available energy of the water into the kinetic formbefore it enters the wheel. In reaction turbines the energy is partlyin the kinetic form and partly in the form of pressure energy. The action in the Girard impulse turbine may be understood byreference to Fig. 316. Water is supplied from A and passes througha ring of guide passages B, B, having blades so shaped as to causethe water to whirl. Immediately under the guide passages is a hori-zontal wheel C, which is fixed to a vertical shaft DD. This wheelhas a ring of blades round its rim bent contrary to the blades in theguide passages. If the wheel were prevented from rotating, theaction of the wheel blades would be to direct the water backwards. ^ JUi A ipm £H 2> E W\ ,,jf,,,..,E E 77-777777777? -77777-777777777777777?77~ Fig. 31
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectphysics
