The Centrifugal-Flow Compressor.
The centrifugal compressor consists basically of an impeller and a diffuser manifold. Other components such as compressor manifold may be added to direct the compressed air into the combustion chamber. As the impeller revolves at high speed, air is drawn in at the eye. Centrifugal force provides high acceleration to this air and causes it to move outward from the axis of rotation toward the rim of the rotor where it is ejected at high velocity and high kinetic energy. The pressure rise is produced in part by expansion of the air in the diffuser manifold by conversion of the kinetic energy of motion into static pressure energy. The centrifugal compressors can be manufactured in a variety of designs including single-stage, multiple-stage, and double-sided types. The centrifugal compressor has a number of features to recommend its use in certain types of gas turbine engines. Chief among its attributes are its simplicity, ruggedness, and low cost. Because of its massive construction, it is much less susceptible to damage from the injection of foreign objects. The centrifugal compressor is capable to relatively high compressor ratio per stage. Above 80 percent efficiency may be reached with a compression ratio of 6 or 7 to 1. Above this ratio, efficiency drops off at a rapid rate because of excessively high impeller tip speeds and attending shock-wave formation. This rules out this type of compressor for use in larger engines since high compression ratios are necessary for low fuel consumption. Some centrifugal-flow engines obtain somewhat higher ratios through the use of multistage compressors. Although the tip speed problem is reduced, efficiency is again lost because of the difficulty in turning the air as it passes from one stage to another. Double-entry compressors also help to solve the high-tip-speed problems, but this advantage is partially offset by the complications in engine design necessary to get air to the rear impeller, and by the requirement of a large plenum or air chamber, where the air from the inlet duct is brought to a slower speed for efficient direction change and higher pressures. The plenum chamber acts as a diffuser by which means the rear impeller can receive its air. Because of the problems inherent in this type of design the centrifugal compressor finds its greatest application on the smaller engines, where simplicity, flexibility of operation and ruggedness are the principle requirements rather than small frontal area, and ability to handle high air flows and pressures with low loss of efficiency.
Post-Reading I. Match these English words with their Russian equivalents:
II. a) Match verbs from the text with their definitions.
- to put smth with another thing or group of things - to make goods in large quantities in a factory - to deliberately let smth fall - to balance the effect of smth, with the result that there is no advantage or disadvantage - to stop considering smth as a possibility
b)Choose any 5 words from the blue banner and explain them.
III. Complete the following sentences using the ideas from the text.
1. The centrifugal compressor consists basically of … 2. The pressure rise is produced in part by … 3. The centrifugal compressors can be manufactured in a variety of designs including … 4. Because of its massive construction, it is much less susceptible to … 5. … may be reached with a compression ration of 6 or 7 to 1. 6. High compression ratios are necessary for … 7. Although the tip speed problem is reduced, efficiency is again lost because of … 8. … help to solve the high-tip-speed problems. 9. The plenum chamber acts as … 10. The centrifugal compressor finds its greatest application on…
IV. Match parts of the sentences in columns A and B.
VI. a) Answer the following questions.
1. What does a centrifugal compressor consist of? 2. What does centrifugal force provide? 3. What is the pressure rise produced by? 4. What types of design of a centrifugal compressor exist? 5. What are the advantages of a centrifugal compressor? 6. Why is a centrifugal compressor much less susceptible to damage from foreign object? 7. When does the efficiency drop off at a rapid rate? 8. By means of what do some centrifugal-flow compressors obtain higher ratios?
b) Think of 3 more questions to the text.
VII. Retell the text.
Language in Use I. Find pairs of synonyms among the words.
II. Find the antonyms among the words.
III. a) Match the adjectives with their definitions.
b) Reproduce the context where they are used.
IV. Fill in the gaps using the words from the oval. Mind, there is one extra word! Translate the sentences into Russian.
2. The earliest __________ of these dynamic turbomachines were pumps, fans and blowers. 3. What differentiates these early turbomachines from compressors is that the working fluid can be considered __________ thus permitting accurate analysis through Bernoulli's equation. 4. In contrast, modern centrifugal compressors are higher in speed and analysis must __________ with compressible flow. 5. For purposes of definition, centrifugal compressors often have density increases __________ than 5 percent. 6. Also, they often __________ relative fluid velocities above Mach 0.3 when the working fluid is air or nitrogen. 7. In __________, fans or blowers are often considered to have density increases of less than 5 percent and peak relative fluid velocities below Mach 0.3 8. In an idealized sense, the dynamic compressor achieves a pressure rise by adding kinetic-energy/velocity to a continuous flow of fluid __________ the rotor or impeller. 9. This kinetic energy is then converted to __________ in static pressure by slowing the flow through a diffuser. V. Use the prepositions in the oval to complete the sentences in the text. Translate the text.
Centrifugal compressors are used _______ industry because they have fewer rubbing parts, are relatively energy efficient, and give higher airflow than a similarly sized reciprocating compressor (i.e. positive-displacement). Their primary drawback is that they cannot achieve the high compression ratio reciprocating compressors _______ multiple stages. Centrifugal fan/blowers are more suited _______ continuous-duty applications such as ventilation fans, air movers, cooling units, and other uses that require high volume _______ little or no pressure increase. _______ contrast, multi-stage centrifugal compressors often achieve discharge pressures of 8,000 _______ 10,000 psi (59 MPa to 69MPa). One example _______ an application _______ centrifugal compressors is their use _______ re-injecting natural gas back _______ oil fields to increase oil production. VI. Fill in the gaps with the suitable derivative of the word given in brackets. Translate the sentences.
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1. Centrifugal compressors, (sometimes referred to as radial compressors) are a special class of radial-flow work-absorbing turbomachinery that __________ pumps, fans, blowers and compressors.
