n. - A water wheel, commonly horizontal, variously constructed, but usually having a series of curved floats or buckets, against which the water acts by its impulse or reaction in flowing either outward from a central chamber, inward from an external casing, or from above downward, etc.; -- also called turbine wheel.
n. - A form of steam engine analogous in construction and action to the water turbine. There are practically only two distinct kinds, and they are typified in the de Laval and the Parsons and Curtis turbines. The de Laval turbine is an impulse turbine, in which steam impinges upon revolving blades from a flared nozzle. The flare of the nozzle causes expansion of the steam, and hence changes its pressure energy into kinetic energy. An enormous velocity (30,000 revolutions per minute in the 5 H. P. size) is requisite for high efficiency, and the machine has therefore to be geared down to be of practical use. Some recent development of this type include turbines formed of several de Laval elements compounded as in the ordinary expansion engine. The Parsons turbine is an impulse-and-reaction turbine, usually of the axial type. The steam is constrained to pass successively through alternate rows of fixed and moving blades, being expanded down to a condenser pressure of about 1 lb. per square inch absolute. The Curtis turbine is somewhat simpler than the Parsons, and consists of elements each of which has at least two rows of moving blades and one row of stationary. The bucket velocity is lowered by fractional velocity reduction. Both the Parsons and Curtis turbines are suitable for driving dynamos and steamships directly. In efficiency, lightness, and bulk for a given power, they compare favorably with reciprocating engines.