REMARKS ON THE EFFICIENCY OF INJECTORS AND EJECTORS

摘要

In various books, the low efficiency of injectors and ejectors is often put in evidence, but without a detailed analysis of the causes. Then, it appears puzzling that injectors were used to feed boilers in small thermal plants of the past.The aim of this paper is a detailed analysis of the efficiency of injectors and ejectors and an examination of the expediency of an injector in comparison with a pump in the case of feeding a boiler with non-preheated water. From a thermodynamic analysis it follows that the two devices have practically equal efficiencies, when the water is not preheated.In addition, by means of exergy analysis one puts in evidence, e.g., that a steam-water injector has a very low efficiency (≈ 2%) when the pressure rise is the only aim, whereas the above efficiency increases notably, even if it remains still low, when also the temperature rise is useful. This reason justifies the different values of injector efficiency quoted in the literature, at least partially.