Ejectors

Visit ejectors, also known as jet devices or are static devices designed to to vacuum, compress or mix gases, vapors, liquids and sometimes solids, thanks to the expansion of a primary driving fluid. This may be gaseous, in subsonic or supersonic conditions, or liquid, in incompressible conditions, and provides the energy needed to drive the secondary fluid.

These devices can also be used to drain a cavity or volume, and in some applications can compete with mechanical vacuum pumps thanks to their absorption capacities of up to 10 ⁶ m ³ .h ^-1 air.

Compared with vacuum pumps, ejectors have the great advantage of costing significantly less than a conventional pump, having no moving parts and therefore requiring virtually no maintenance, and being highly resistant to corrosion or attack by aggressive gases or solid particles. However, they do not always replace mechanical vacuum pumps, due to their narrower operating range and higher energy consumption. In some applications, a combination of ejector and liquid ring pump is recommended.

In addition to their use in vacuum production, ejectors are used in a wide variety of applications, from the chemical industry for mixing fluids or desalinating water, to the aeronautics industry, where ejectors are used to increase propulsion or reduce the noise of thrusters, to refrigeration production, where the ejector, coupled to a heat source (which may be of renewable origin), ensures the compression of a refrigerant.

Ejector applications depend essentially on the nature of the fluids used. Given the large number of possible combinations of different fluids, it is not possible to describe the fundamental physical laws governing the operation of all these devices. However, in order to give the engineer a rough idea of the sizing and characteristics of the device he or she needs, we will deal with the three main combinations:

• liquid jet ejectors,

• gas jet ejectors,

• steam jet ejectors.

The first combination concerns incompressible fluids, while the other two relate to compressible fluids.

It should be pointed out that there are several manufacturers on the market, a non-exhaustive list of which is given in the appendix, who offer more or less detailed catalogs of standard equipment, or who are perfectly capable of studying and carrying out any particular...