PURPOSE AND SCOPE OF ESDUPAC A9242 ESDU 92042 provides details of a computer program@ ESDUpac A9242@ for use in the design and performance evaluation of ejectors and jet pumps in which the working fluids are gases. ESDUpac A9242 provides the following design and performance prediction procedures. (i) Quick Design Procedure. Given a selection of entry and required exit pressures@ temperatures@ mass flow rates and dimensions the program will calculate primary nozzle and exit dimensions@ using empirical data for air-air ejectors. Note that the scope of the Quick Design Method is restricted to ejectors with constant area mixing and air as both working fluids. (ii) Detailed Design Procedure. Given a selection of entry and required exit pressures@ temperatures@ mass flow rates@ dimensions and loss factors as well as four user defined constraints on the flow conditions@ the program will calculate primary nozzle and exit dimensions and flow conditions throughout the ejector using the procedure outlined in Section A12 of Appendix A. (iii) Performance Prediction Calculation. Given the ejector dimensions@ loss factors and a range of flow conditions at entry@ the program will calculate the outlet conditions and the flow conditions throughout the ejector@ using the procedure outlined in Section A13 of Appendix A. Section 5 describes the required input data. A number of examples which illustrate the use of the program are presented in Section 7. The full analysis for the computer program is presented in Appendix A. In many ejectors@ the primary fluid is compressed air or gas and the secondary inlet conditions are often set by existing pipework. In the design procedure the program optimises for the shortest mixing duct length for complete mixing of the primary and secondary fluids and for the highest efficiency. The program allows a design requirement for a particular pressure and/or mass flow characteristic at the exit of the ejector to be met. The ejector design procedures determine performance at the primary nozzle 'on-design' point. There are a number of situations in which this approach will be inadequate. The ejector may be required to operate over a range of primary pressures or secondary Mach numbers@ in which case estimates of 'off-design' performance must be sought. Performance prediction is also necessary if an existing plant item@ with all physical dimensions known@ needs to be assessed for a particular application. Performance prediction can be considered as almost the reverse of the design process in that solutions to what were design criteria are now required@ with the physical dimensions of the device being known. The calculation procedure presented in Appendix A is applicable to non-reacting gases which can be modelled as ideal and to ejectors with mixing ducts of circular (either cylindrical or conical) section. The methods are based on the equations of continuity and of momentum and energy conservation.