Chapt06

Engineers have always designed diffusers to increase

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Unformatted text preview: . Consider the flat-walled diffuser in Fig. 6.26a, where section 1 is the inlet and section 2 the exit. Application of Bernoulli’s equation (6.112) to this diffuser predicts that or V2 1 p2 Cp,frictionless p01 1 1 2 p1 1 2 V2 2 V2 V1 p02 2 (6.114) Meanwhile, steady one-dimensional continuity would require that Q V1A1 V2A2 (6.115) Combining (6.114) and (6.115), we can write the performance in terms of the area ratio AR A2/A1, which is a basic parameter in diffuser design: Cp,frictionless 1 (AR) 2 (6.116) | v v A typical design would have AR 5 1, for which Eq. (6.116) predicts Cp 0.96, or nearly full recovery. But, in fact, measured values of Cp for this area ratio [14] are only as high as 0.86 and can be as low as 0.24. | e-Text Main Menu | Textbook Table of Contents | Study Guide 6.9 Experimental Duct Flows: Diffuser Performance 383 Thin boundary layers Low velocity, high pressure (a) Backflow Thick boundary layers High velocity, low pressure Fig. 6.27 Diffuser performance: (a) ideal pattern...
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