- 行业: Printing & publishing
- Number of terms: 178089
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- Company Profile:
McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
A machine for converting the heat energy in steam to mechanical energy of a moving mechanism, for example, a shaft. The steam engine dominated the industrial revolution and made available a practical source of power for application to stationary or transportation services. The steam power plant could be placed almost anywhere, whereas other means of power generation were more restricted, experiencing such site limitations as an elevated water supply, wind, animal labor, and so on. The steam engine can utilize any source of heat in the form of steam from a boiler. It was developed in sizes which ranged from that of children's toys to 25,000 hp (18.6 MW), and it was adaptable to pressures up to 200 lb/in.<sup>2</sup> (1.4 megapascals). It reached its zenith in the nineteenth century in stationary services such as drives for pumping plants; drives for air compressor and refrigeration units; power supply for factory operations with shafting for machine shops, rolling mills, and sawmills; and drives for electric generators as electrical supply systems were perfected. Its adaptability to portable and transportation services rested largely on its development of full-rated torque at any speed from rest to full throttle; its speed variability at the will of the operator; and its reversibility, flexibility, and dependability under the realities of stringent service requirements. These same features favored its use for many stationary services such as rolling mills and mine hoists, but the steam engine's great contribution was in the propulsion of small and large ships, both naval and merchant. Also, in the form of the steam locomotive, the engine made the railroad the practical way of land transport. Most machine elements known today had their origin in the steam engine: cylinders, pistons, piston rings, valves and valve gear crossheads, wrist pins, connecting rods, crankshafts, governors, and reversing gears.
Industry:Science
A machine for generating mechanical power in rotary motion from the energy of steam at temperature and pressure above that of an available sink. By far the most widely used and most powerful turbines are those driven by steam. In the United States well over 85% of the electrical energy consumed is produced by steam-turbine-driven generators. Individual turbine ratings historically have tended to follow the increasing capacity trend but have reached limits imposed by material and machine design considerations. The largest unit shipped during the 1950s was rated 500 MW. Units rated about 1100 MW were in service by the close of the 1960s, and ratings up to 1300 MW saw frequent application in the 1970s and early 1980s. Units of all sizes, from a few horsepower to the largest, have their applications.
Industry:Science
A machine for generating rotary mechanical power from the energy in a stream of fluid. The energy, originally in the form of head or pressure energy, is converted to velocity energy by passing through a system of stationary and moving blades in the turbine. Changes in the magnitude and direction of the fluid velocity are made to cause tangential forces on the rotating blades, producing mechanical power via the turning rotor.
Industry:Science
A machine for moving fluid by accelerating it radially outward. More fluid is moved by centrifugal pumps than by all other types combined. The smooth, essentially pulsationless flow from centrifugal pumps, their adaptability to large capacities, easy control, and low cost make them preferable for most purposes. Exceptions are those in which a relatively high pressure is required at a small capacity, or in which the viscosity of the fluid is too great for reasonable efficiency.
Industry:Science
A machine for the shaping of long, flat, or flat contoured surfaces by reciprocating the workpiece under a stationary single-point tool or tools. Usually the workpiece is too large to be handled on a shaper.
Industry:Science
A machine in which mechanical energy is converted to electrical energy. Generators are made in a wide range of sizes, from very small machines with a few watts of power output to very large central-station generators providing 1000 MW or more. All electrical generators utilize a magnetic field to produce an output voltage which drives the current to the load. The electric current and magnetic field also interact to produce a mechanical torque opposing the motion supplied by the prime mover. The mechanical power input is equal to the electric power output plus the electrical and mechanical losses.
Industry:Science
A machine mounted on flanged wheels which converts some form of potential energy into the mechanical work of propelling itself and other, nonpowered vehicles over a railroad track. The dimensions and weight of a locomotive are restricted by the presence of stationary structures adjacent to and above the track, such as overhead bridges and tunnels, and by the strength of the track and bridges that support it.
Industry:Science
A machine that converts mechanical power into alternating-current electric power. Almost all electric power is produced by alternating-current (ac) generators that are driven by rotating prime movers. Most of the prime movers are steam turbines whose thermal energy comes from either fossil or nuclear fuel. Combustion turbines are often used for the smaller units and in cases where gas or oil is the available fuel. Where water power is available from dams, hydroelectric ac generators are powered by hydraulic turbines. Small sites may also use diesel or gasoline engines to drive the generator, but these units are usually used only for standby generation or to provide electric power in remote areas.
Industry:Science
A machine that draws a fluid into itself through an entrance port and forces the fluid out through an exhaust port (see <b>illus.</b>). A pump may serve to move liquid, as in a cross-country pipeline; to lift liquid, as from a well or to the top of a tall building; or to put fluid under pressure, as in a hydraulic brake. These applications depend predominantly upon the discharge characteristic of the pump. A pump may also serve to empty a container, as in a vacuum pump or a sump pump, in which case the application depends primarily on its intake characteristic.
Industry:Science
A machine that increases the pressure of a gas or vapor (typically air), or mixture of gases and vapors. The pressure of the fluid is increased by reducing the fluid specific volume during passage of the fluid through the compressor. When compared with centrifugal or axial-flow fans on the basis of discharge pressure, compressors are generally classed as high-pressure and fans as low-pressure machines.
Industry:Science
