One way or another, you most likely have heard about ejectors. They are also otherwise called surface jet pumps, educators, and velocity spools. Though the names are different, the device follows the same operating principle. By definition, an ejector is a simple, static device that is utilizing the energy contained in a highly pressurized fluid, either gas or fluid, to compress a low-pressure suction fluid to intermediate discharge pressure.
This operation follows the famous concept called Bernoulli’s Principle. It simply means as the fluid’s velocity increases, its pressure decreases. The opposite is also true. The device works by increasing the already high-pressure stream or the motive fluid through an adiabatic expansion in the nozzle. As the pressure of the motive fluid drops, it generates a low-pressure zone before the mixing chamber. This is located around the nozzle tip where the velocity is highest or which is often referred to as the suction chamber.
As the pressure in the suction chamber is low, the suction fluid starts to move towards it and mixes with the motive fluid. As the mixed fluid reaches the diverging portion or the diffuser section of the ejector, the velocity is then converted into pressure energy. More importantly, as the part of the energy has been used to perform the task on the suction stream, the discharge pressure is now between the suction and motive pressures.
When it comes to installation, an ejector can be installed in different orientations. The only major consideration is to have a device that can remove the solid particles or condensate from the entrained gas as it may decrease the throughput capacity of the device. A drain valve would be a better option for this.
So, that’s how ejectors work, applying Bernoulli's principle or the interplay between pressure and velocity.
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