Abstract:

ESDU 88014 introduces a computer program that predicts the operating characteristics of air-lift pumps. Such pumps operate by injecting air near the bottom of a riser so creating a two-phase flow that rises due to its density difference from that of the surrounding liquid, or liquid in a downcomer. Because there are no moving parts the pumps are virtually maintenance free and so provide a reliable means of raising corrosive, hazardous or abrasive liquids. Operating characteristics and design features are briefly discussed. The program applies to isothermal flow of a Newtonian liquid. It is based on the drift-flux model, which is explained, and uses empirical correlations from the literature to predict the gravity and friction components of pressure loss. Comparison with experiment shows predictions are generally within 30 per cent which compares favourably with two-phase correlations. However, because of that limitation, the prime uses of the program are either to modify an existing design, when the program can first be calibrated against experiment and then used to predict the effect of design changes, or to carry out a sensitivity analysis of a basic pump design. Guidance is given on the format for the input data and typical values are provided for equivalent hydraulic roughness and pressure losses in pipe fittings, data for which are required by the program. Both uses of the program are illustrated in worked examples that include specimen print-outs.