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Unformatted text preview: loss; hence large
Cp means a successful diffuser. From Fig. 6.23 the minimum loss (maximum recovery) occurs for a cone angle 2 equal to about 5°. Angles smaller than this give a large
Moody-type loss because of their excessive length. For cone angles greater than 40 to
60°, the loss is so excessive that it would actually be better to use a sudden expansion.
1.2 1.0 Fully developed inlet flow 0.8 Thin inlet boundary layer K
0.6 2θ V1 V2 0.4 K= 0.2 hm
V 1/(2g) =1– d4
2 – Cp 0
0 20 | v v Fig. 6.23 Flow losses in a gradual
conical expansion region. | e-Text Main Menu 40 60 80 100 120 Total included diffuser angle 2 θ , degrees | Textbook Table of Contents | Study Guide 140 160 180 Chapter 6 Viscous Flow in Ducts This unexpected effect is due to gross flow separation in a wide-angle diffuser, as we
shall see soon when we study boundary layers. Reference 14 has extensive data on diffusers.
For a gradual contraction, the loss is very small, as seen from the following experimental values :
Contraction cone angle...
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- Spring '08