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September 19, 2018 08:24

Best Placement for a Fan in a Convergent - Divergent System

Best Placement for a Fan in a Convergent - Divergent System

 Let us assume a system formed by a convergent nozzle (Inlet), a throat, a fan, and a divergent nozzle (Exit), as shown schematically in Figures (a)and (b) above. The cross-sectional areas of the convergent nozzle, the throat, and the divergent nozzle as seen by the airflow are A1, A0 and A2, respectively. Additionally, let us suppose that A1 = A2 = 1780 cm2, and A0 = A1 / 2 = 890 cm2. The fan is driven by an electric motor whose power rating is PM = 1500 W.  When the motor is operating at its maximum power rating, let us assume an airflow is exhausted to the atmosphere with a velocity Vφ2 = 20 m/s. I would like the answer to the following questions:

Q1. Which is the best position for placing the fan in the system, as in Fig. (a), or as in Fig. (b), in such a way as to obtain minimum pressure on the fan, and minimum fan noise?

Q2. If the exhaust velocity is Vφ2 = 20 m/s, can we infer that the airflow velocity in the throat would be Vφ0 = 40 m/s?

 

 

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