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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 11a Key components <strong>of</strong> the G-lader supercharger. At the top are the two<br />

halves <strong>of</strong> the housing with the fixed G-shaped spiral chambers. In the lower left is the<br />

G-shaped rotating element that mates with the spiral in the housing. The shaft<br />

element that provides the oscillating motion is shown in the right corner. (Courtesy<br />

Volkswagen AG.)<br />

in the next section on turbochargers apply to the mechanically driven<br />

compressor as well.<br />

While a single-stage radial-flow compressor can provide a high<br />

pressure ratio, very high rotational speeds are required if the compressor<br />

is to be kept to a reasonable size. Unlike positive-displacement-type<br />

compressors, kinetic devices do not displace the same volume <strong>of</strong> air during<br />

each revolution. Therefore, in a centrifugal compressor, output pressure is<br />

proportional to the square <strong>of</strong> the rotational speed. Compressor speeds <strong>of</strong> up<br />

to 25,000 rpm may be needed before any noticeable positive boost pressure<br />

above atmospheric pressure is achieved. Since the input speed to the<br />

Copyright © 2003 Marcel Dekker, Inc.

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