'Jet Apparatus' is a term typically used to identify a piece of equipment that uses a fluid under pressure (liquid/gas/vapor), to perform work on, and in direct contact with, another medium (liquid/gas/vapor/granular solid), in a defined, predictable way.
The main principle governing the operation of typical Jet-Apparatus is Conservation of Momentum. When fluid pressure (potential energy), is converted into fluid velocity (kinetic energy), by means of a constricting orifice (i.e. Converging Nozzle), there exists an associated useful pressure drop. For a constant primary fluid mass flowrate and constricting orifice, this pressure drop is a function of the primary fluid pressure. Jet-Apparatus uses this pressure drop to entrain a secondary medium (fluid or granular solid), within a chamber (i.e. Suction Chamber), that is at the pressure of the secondary medium, for the purpose of pumping, mixing, evacuating, etc. The Suction Capacity of a specific device is typically a function of the primary fluid velocity and mass flowrate [as well as properties of the suction material and downstream pressure]. Once entrained, the velocity of the mixture of primary and secondary media (kinetic energy), is converted back into pressure energy (potential), by means of a volumetric divergence (i.e. Diffuser). Available Discharge pressure is typically a function of the diffuser velocity and total mass flowrate. The three main components of Jet-Apparatus (Converging Nozzle, Suction Chamber,Diffuser), are rigidly fixed in specific relation to each other, hence there are no moving parts, one of the main advantages to this type of device.
The efficiency of a jet apparatus does not exceed 30 percent. However, the advantages of such apparatus, including the possibility of increasing the pressure of the drawn fluid without the use of moving parts, the simplicity of design, and operational reliability, have led to applications in many branches of engineering. Mechanical pumps, compressors, and blowers are more economical at high heads and when consumption of the compressible fluid is high, but they are also more complex.