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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exothermic action. A chemical action in which heat energy is released. expanded plastic. A plastic resin whose volume has been increased by bubbles of gas which are generated when the constituents of the plastic are mixed. Expanded plastic is also known as foamed plastic. expanded-scale meter (electrical meter). A current-measuring analog electrical indicator whose needle deflection is not uniform over its entire scale. The amount of deflection for a given input is increased for certain ranges of indication. Expanded-scale meters are used when small changes in the upper limit of the value being measured are important. expander-tube brake (aircraft brake). A type of lightweight, nonenergizing, hydraulically operated aircraft brake. A synthetic rubber tube is installed around the brake housing mounted on the landing gear axle, and blocks of brake lining material are held pressed against the expander tube with flat metal springs. The brake drum, mounted inside the wheel, rotates around the linings. When the brake pedal is depressed, hydraulic fluid is forced into the tube. The tube expands and forces the brake blocks against the rotating brake drum. This force applies enough friction to the drum to slow the rotation of the wheel. expansion reamer (metal-cutting tool). A precision cutting tool used to smooth the inside of a drilled hole and enlarge it to an accurately specified dimension. The diameter of the hole cut by an expansion reamer can be increased a few thousandths of an inch by adjusting a wedge inside the blades to move them outward. expansion turbine (air-cycle air conditioning system component). A small turbine in an air-cycle cooling system that extracts energy from compressed air as it drives a compressor. Bleed air containing a large amount of energy is taken from the turbine-engine compressor. This hot air passes through a primary heat exchanger where it gives up some of its energy. It is then taken into a compressor driven by the expansion turbine. Here its pressure and temperature are both increased. This air then passes through a secondary heat exchanger where it gives up more of its energy and its temperature is dropped. From here it flows into the expansion turbine that drives the compressor, using up much of its remaining energy. After leaving the turbine, it expands into the air conditioning ducts. Having lost most of its energy through the heat exchangers and the expansion turbine, the air is now cold. expansion wave (high-speed aerodynamics). The change in pressure and velocity of a supersonic flow of air as it passes over a surface, which drops away from the flow. As the surface drops away, the air tries to follow it. In changing its direction, the air speeds up to a higher supersonic velocity, and its static pressure decreases. There is no change in the total amount of energy as the air passes through an expansion wave, and so there is no noise as there is when air passes through a shock wave.
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