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Text 4. Centrifugal compressors
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Do the following tasks:
1) Give the written translation of the text.
2) Name the advantages of centrifugal compressors.
Centrifugal compressors
Multistage centrifugal blowers when capable of handling gases against pressures greater than 35 psig are generally classed as compressors. They resemble multistage centrifugal pumps, and many of the problems encountered in their design are similar to those encountered in pump design. The impellers of a complete centrifugal compressor unit are of the single-suction type, and passages lead the air or gas from the discharge of one impeller to the suction side of the next impeller.
Because of an increase in temperature of the gas or air as the pressure is increased, cooling is generally necessary. If the pressures are not high, cooling water circulated in labyrinths between impellers may be sufficient. When high pressures are encountered, the gas may be cooled in inter stage coolers. The reason for maintaining the gas at a low temperature is to permit an increase in the mass rate of flow with a corresponding reduction in size and horsepower.
Axial-flow compressors are designed on the principles of the airfoil section, and the blade shapes will be similar to the axial-flow fan.
These compressors are an essential part of the gas-turbine cycle. The gas is not cooled between stage, because a portion of the additional work necessary to compress the gas adiabatically over the work necessary to compress it isothermally will be recovered in the gas turbine. The advantages of centrifugal and axial-flow blowers and compressor are: 1) non-pulsating discharge of the gas, 2) no possibility of building up excessive discharge pressures, 3) a minimum of parts subject to mechanical wear, 4) no valve necessary, 5) a minimum of vibration and noise, 6) high speed, low cost, and small size or high capacity.
Text 5. Pumps and compressors
Do the following tasks:
1) Give a written translation of the text into English.
2) Retell the text.
Насосы – машины для перемещения капельных жидкостей. Поршневые насосы в теплоэнергетике используются для питания водой котлов небольшой производительности; главным же образом используются турбонасосы, центробежные и аксиальные насосы. Назначение насоса состоит в преодолении сопротивлений, возникающих при перемещении жидкости.
Компрессоры – машины, предназначенные для перемещения и сжатия упругих (сжимаемых) жидкостей (газов). Компрессоры на тепловых электрических станциях в основном применяют в качестве вспомогательной машины газотурбинных установок.
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Машины для перемещения и сжатия воздуха называют вентиляторами. Назначение вентилятора в котельных установках – нагнетать воздух в топку, то есть, осуществлять дутье, и поэтому его называют дутьевым вентилятором.
Unit 4
Memorize the words
shell-кожух, обшивка; корпус; оболочка; вкладыш
tubular- трубчатый
vessel- сосуд, резервуар, бак, баллон
combustion-горение; сгорание, окисление
waterline-ватерлиния, контур водоёма
inclination-наклонение; уклон; наклон; откос, скат
shape-форма; очертание; вид, образец
header-головная часть, водяная камера; водяной коллектор (водотрубного котла); водосборник
row-ряд
connection-соединение; разъём, труба; трубопровод; секция
Text 1. Boilers
Do the following tasks:
1) Do a translation of the text into Russian.
2) Make up 10 questions about the text and let your neighbor answer them, then change parts.
Boilers
Fire-tube boilers. These are boilers with straight tubes that are surrounded by water and through which the products of combustion pass. The tubes are usually installed within the lower portion of a single drum or shell below the waterline.
Water-tube boilers. These are boilers I which the tubes themselves contain steam or water, the heat being applied to the outside surface. The tubes are usually connected to two or more drums set parallel to, or across, the centerline. The drums are usually set horizontally.
Tube shape and position. The tubular heating surface may be classified: 1) by form – either straight, bent, or sinuous or 2) by inclination – horizontal, inclined, or vertical.
Firing. The boiler may be either a fired or an unfired pressure vessel. In fired boilers the heat applied is a product of fuel combustion. A non-fired boiler has a heat source other than combustion.
Circulation. The majority of boilers operate with natural circulation. Some utilize positive circulation in which the operative fluid may be forced “once through” or controlled with partial recirculation.
Furnace position. The boiler is an external combustion device in that the combustion takes place outside the region of boiling water. All heat must be transferred through the heating surface to reach the water. The relative location of the furnace to the boiler is indicated by the description of the furnace as being internally or externally fired: 1) the furnace is internally fired if the furnace region is completely surrounded by water-cooled surfaces; 2) the furnace is externally fired if the furnace is auxiliary to the boiler or built under the boiler.
General shape. During the evolution of the boiler as a heat producer many new shapes and designs have appeared. Some of these boilers have become popular and are widely recognized in the trade, including the following:
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1) Fire-tube boilers – horizontal return tubular, short firebox, compact, locomotive, vertical tube (steam jenny), Scotch type, and residential units.
2) Water-tube boilers – both horizontal straight tube and bent tube units. The horizontal straight tube boiler may have a box type header made of steel plate, or a sectional header each section of which connects
The tubes in a single vertical row. The bent tube boiler may have one to four drums. If the drums is parallel to the tubes, the boiler is long – longitudinal drum; if across the tubes, it is a cross drum. If the furnace is enclosed with water-cooled surfaces, it is a water wall (water-cooled) furnace.
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