# Gas dynamics and ejectors

1. Jun 3, 2014

### rppearso

Does anyone have a good reference to calculate an ejectors required motive gas rate.

As I understand it the pressure of the motive gas out of the nozzle and the pressure of the process gas are the same. A mass/volume flow can be guessed and the properties on the inlet can be calculated using a gas law. The gas then travels through the convergent section of the ejector - how is the pressure calculated in that section? Since the mass is known on the front end that same mass has to travel through the convergent section but the pressure actually increases due to the momentum of the motive gas.

Just because it is an ejector does not nesecarily mean that the flow through the convergent section is sonic so would it have to be assumed that the velocity out of the motive gas is the same as the velocity in the convergent section?

I don't think that's a good assumption though.