(A description of the energy balance is also availabe: See Energy Balance )
Data is entered into the highlighed fields and the program is RUN. In the case (steam ejector) below the motive gas pressure is varied, while entrained gas pressure and entrainment ratio are kept constant.
Results and Analysis of ejectors using our software : Discussion and guidelines, what to look for, design curve versus operating curve
The entrainment ratio can then be varied, to generate ejector curves like the one below. (PR is the ratio of motive gas to entrained gas pressure). Note that these curves are for specific temperatures and gas properties and will change significantly if any of these change.
Each point on the curves above represents performance for an ejector that has been sized for the specific conditions.
The particular ejector selected will have the correct geometry for optimal performance at one particular design point. As the operating point moves away from the design point, performance will deviate increasingly from the ideal curves above. The motive gas pressure and flow rate are kept relatively constant - the control systems maintain the balance between entrained gas pressure and flow and the discharge pressure. This is particularly relevant for vacuum ejectors.
A computer program has been developed that determines the performance curve for a specific ejector geometry. If there is an interest in this program, it could be made available. Additional aspects such a breakpoint analysis could be included.
The breakpoint occurs when the back pressures exceeds the maximum discharge pressure that the ejector can maintain even for zero entrainment. At above this back pressure, reverse flow of entrained gas will occur. This is partcularly relevant to vacuum systems - refer to the graph of a typical case below.