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Handbook of air conditioning and refrigeration / Shan K

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20.18 CHAPTER TWENTY<br />

Inlet System Effect<br />

Consider a 90° elbow that is connected to the fan inlet with a very short connecting duct between<br />

the elbow <strong>and</strong> the fan inlet. Eddies, large-scale turbulence, <strong>and</strong> a nonuniform velocity pr<strong>of</strong>ile form<br />

after the elbow <strong>and</strong> are not smoothed to a uniform velocity distribution because <strong>of</strong> the short connecting<br />

duct. Air enters the fan with a nonuniform velocity pr<strong>of</strong>ile that is quite different from the<br />

FIGURE 20.5 Inlet system effect: (a) inlet system effect on the �pt � V˙<br />

diagram; (b) fan test unit at laboratory;<br />

(c) round elbow before fan inlet.

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