Characteristic values
The following characteristic values can be used to describe the behaviour of an ejector and to design a system:
Pressure ratio
The pressure ratio indicates the ratio of the pressure at the outlet of the ejector to the suction pressure.
∏ = pdiffuser, off / psuction pressure
Pressure lift
The pressure lift indicates how much the pressure of the suction mass flow has been raised to the outlet level (see Schematic representation of a controllable high pressure ejector with pressure and velocity curve of the mass flows and figure below).
Δp = pdiffuser, off - psuction mass flow, on
Mass flow ratio
The mass flow ratio is the quotient of suction mass flow to motive mass flow.
Ø = ṁsuction / ṁmotive
Ejector efficiency
The ejector efficiency is the ratio of the energy that can be gained by expanding the ejector's motive mass flow to the work done by the pressure lift of the motive mass flow and suction mass flow at the ejector outlet. In simplified form, ejector efficiency is defined as follows:
Design example of a low lift ejector created with the help of BITZER SOFTWARE see here.
Design example of a high lift ejector created with the help of BITZER SOFTWARE see here.