TURBINE, literally that which spins or whirls around; in mechanics, a wheel which rotates by the aid of flowing water, air or steam and thus furnishes motive power for machinery. Although the steam-turbine is as old as the Christian civilization it is only within the last half century that it has been fully de veloped. The ordinary turbine with which we arc most familiar is the horizontal water wheel made to rotate by the escape of water through orifices, under the influence of pressure derived from a fall.
Water-Turbine.— There are three recog nized types of the water-turbine, (1) the ra dial; (2) axial; (3) combined or mixed-flow. Turbine wheels are made in various sizes from five to seven feet in diameter, with still larger sizes for extraordinary purposes. Perhaps the most powerful water-turbines in the world arc those installed in 1894-95 for utilizing the power of Niagara Falls (q.v.). The supply of water to the turbine is regulated by a gate or gates, which can partially or entirely close the orifice where the water enters or loaves. The speed of a turbine is regulated by opening and closing the gate which admits the water. Where the power used fluctuates, the speed will fluctuate unless some method is adopted to adapt the power developed to the power utilized. This is usually done by means of a governor, which is so devised that when little power is being used the resulting increase in speed will actuate it to close partly the gate, and when much power is being used, the decrease in speed will actuate it to open the gate wider.
High and Low Pressure.— Turbines are di vided into high and low pressure, the former being relatively small, revolving at a high speed, driven by elevated heads of water. The low pressure turbines are relatively larger, contain a larger volume and run at a lower rate. In the Black Forest, Germany, turbines are running with heads of 72 and 354 feet, and having diameters of 20 and 13 inches, respectively. Low-pressure turbines perform excellent duty with large volumes of water having only nine inches head.
The Radial Turbine.— In radial turbines the water in passing through the wheel flows in a direction at right angles to the axis of rotation or approximately radially. The water may flow inward from the circumference to the centre or outward from the centre toward the circumfer ence. The best-known type of the inward flow is the Francis turbine, and of the outward flow the Fourneyron turbine.
The Axial Turbine, or parallel flow as it is sometimes called, is one in which the water flows through in a direction generally parallel with the axis of rotation. The water may flow from the top downward or from the bottom upward. The best known type of the down ward flow is the Jonval turbine.
The Combined Turbine, or mixed flow, is any combination of the radial or axial; that is, the water may flow inward and up or down or outward and up or down. Still another classifica tion is made to distinguish reaction turbines from impulse turbines. In the reaction tur bine all parts are filled with moving water, while in the impulse turbine the buckets or other parts are only partly occupied by the water passing over them, the atmosphere having access to the remaining space. A reaction turbine is driven by the dynamic pressure of the water, which may be under a certain static pressure, due to the fact that the inflow takes place under pressure, since the wheel is always filled with water. In the impulse turbine the inflow takes place freely against .air pressure only. Most turbines are built on the reaction principle. For a more detailed description of water tur bine see HYDRAUT.ICS ; WATER-WHEEL.
The Steam-Turbine.-- The earliest known steam-turbine was that invented by Hero which is described in an Alexandrian manuscript of about 120 B.C. This was not a practical inven tion, however, being merely a toy. Little prog ress was made in the turbine up to the 17th century. Branca made an impulse steam-tur bine in 1624, and Edward Somerset followed with a device in 1650. The French engineer Tournaire is entitled to particular mention as having in 1853 indicated the capabilities of the steam-turbine. But the general introduction of the steam-turbine since 1890 is due to the Swed ish engineer De Laval and to C. A. Parsons. Thus it is acknowledged that the progress of the steam-turbine is wholly modern and mainly recent. Only after evolution of the modern mathematical sciences could its action be un derstood and the machine be properly designed; only after modern tools and methods of me chanical construction had become refined could it be built in safe and economical forms. The influence of the H‘ro toy or Alexandrian in vention upon modern engineering is shown to have been of great value. The Hero idea lay dormant during nearly 2,000 years which elapsed between the days of Greek philosophy and modern, practically applied, science.