时间：2011-03-11 23:13来源：蓝天飞行翻译 作者：admin 点击：次
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head wind (aircraft flight). A wind which blows from the direction the aircraft is flying. The ground speed of an aircraft (the speed the aircraft is moving over the ground) is less than the speed through the air by the velocity of the head wind. hearth furnace. A type of furnace used to melt iron and steel. The metal is melted by passing hot gases over the charge of metal on the floor, or hearth, of the furnace. heat. A form of energy that affects the speed of movement of the molecules of which a material is made. The more heat energy in a material, the faster its molecules move, and the amount of heat energy in a material determines its physical condition. Water that contains very little heat energy is a solid, ice. When heat is added to ice, the ice melts and becomes liquid water. Additional heat added to the liquid water causes it to boil, and it becomes water vapor (steam). Our chief source of heat energy is the sun. Heat energy from the sun reaches the earth by radiation, and it is stored in plants and animals in the form of chemical energy. This chemical energy can be changed back into heat energy by the use of various types of machines. heat engine. A form of mechanical device that converts heat energy into mechanical energy. The two most widely used types of heat engines for aircraft are reciprocating engines and turbine engines. heater (electron tube). A small strip of resistance wire mounted inside a tubular cathode in an electron tube. Low-voltage AC flowing through the heater causes it to get red-hot. This heats the cathode enough for it to emit, or give off, electrons. heat exchanger. A device used to exchange heat from one medium to another. Radiators, condensers, and evaporators are all examples of heat exchangers. Heat always moves from the object or medium having the greatest level of heat energy to a medium or object having a lower level. Air-to-air, air-to-liquid, liquid-to-air, and liquid-to-liquid heat exchangers are commonly used with aircraft engines. heating element (electrical heater). A coil or a piece of resistance wire connected across a source of electrical energy. The resistance of the element is high enough that current flowing through it produces enough heat to cause it to glow red-hot. heat lamp. A form of incandescent lamp that produces a maximum of infrared radiation (heat) with a minimum of visible light rays. Heat lamps are used for curing resins, drying paint, keeping food warm, and applying heat to parts of the human body. heat load (air conditioning system). The amount of heat that must be added to or taken away from the inside of an aircraft cabin, during a specified unit of time, to keep the temperature of the cabin constant. heat pump. A device that moves heat from one location to another. An air conditioning system is a form of heat pump. Heat from inside the aircraft cabin is absorbed by a liquid refrigerant. When the refrigerant absorbs the heat, it evaporates, or changes into a gas. The gas is then compressed, and the compression raises its temperature higher than that of the outside air. |
