How does a steam ejector create a vacuum?

The principle of the vacuum generated by the steam ejector is mainly based on the principles of fluid mechanics and energy conversion. The following are the basic steps for a steam ejector to create a vacuum:

High-pressure steam input

Steam (working fluid) with a certain pressure is fed into the nozzle of the steam ejector (Laval nozzle).

Conversion of pressure energy to kinetic energy

When high-pressure steam passes through the nozzle, the flow rate of the steam gradually increases and the pressure gradually decreases due to the gradual reduction of the cross-sectional area of the nozzle. In this process, the pressure energy of the steam is converted into kinetic energy, forming a supersonic jet.

Vacuum formation

At the outlet of the nozzle, a vacuum is formed at the rear of the nozzle due to the extremely high vapor flow rate and the pressure is very low. This vacuum area is the key to the vacuum generation of the steam ejector.

Suction action

Due to the presence of  vacuum area, the pumped fluid, such as air or other gases, is drawn into the suction chamber.

Mixing and energy exchange

The pumped fluid and the working fluid are mixed in the mixing chamber and the mass, momentum and energy are exchanged. In this process, the velocity of the working fluid gradually decreases, while the velocity of the pumped fluid gradually increases, until the two gradually converge at a certain section of the mixing section to form a single and uniform mixed fluid.

Diffuser and pressurization

The mixed fluid enters the diffuser (diffusion chamber), and due to the gradual increase of the cross-sectional area of the diffuser, the speed of the mixed fluid gradually decreases and the pressure gradually increases. When the mixed fluid is discharged from the diffuser, the pressure is already above atmospheric pressure, the purpose of pumping is achieved, and a vacuum is created.
It is important to note that the vacuum generated by the steam ejector is related to factors such as the pressure, temperature, flow rate of the incoming steam, and the nature of the fluid being pumped. Therefore, when designing and using steam ejectors, it is necessary to select the appropriate parameters and models according to the specific situation to obtain the required vacuum level.