Abstract:

ESDU 94046 introduces a program (ESDUpac A9446) for ejectors in which the primary and secondary flows are non-reacting gases that can be modelled as real. Three procedures are provided: a Quick Design Procedure, a Detailed Design Procedure and Performance Prediction. The first is based on experimental data obtained for steam ejectors pumping air at 20 degrees C. If other gases are handled the secondary mass flow rate is converted by the program to an equivalent rate based on the molar mass of the secondary gas. For the second the input is a selection of entry and required exit pressures and flow rates, together with estimates of loss coefficients in the primary and secondary nozzles, mixing duct and diffuser. The program will optimise the ejector, calculating the primary nozzle and exit dimensions, and flow conditions throughout. For the third case, the ejector dimensions are input together with the loss factors again and a range of entry flow conditions and the program will calculate flow conditions throughout the ejector and at exit. The equations on which the program is based are fully specified, the input format required is set out in clear tables, and three worked examples illustrate the use of the procedures. Notes are provided on the mechanical design of steam/gas ejectors including the use of multi-stage units and annular- or multi-nozzles. Possible operating problems are discussed.