Spindle Ejector

Ejectors can claim to have the simplest configuration among vari-ous systems for vapor compression. In contrast to other apparatus, ejectors consist of a single unit connected to the tubing for motive, suction, and discharge streams. It must be taken into account that any ejector is a compromise between the demands for economical steam consumption and, conversely, not too great a sensitivity toward fluctuations in the operating conditions. An ejector must be designed to match the system operating con-ditions accurately; otherwise, either the efficiency of that system will be impaired or it will not work at all. The economical integra-tion and satisfactory operation of steam ejectors is achieved only if they are accurately adapted and designed for the nominal operation conditions of a system. Often it is advisable or even necessary to adapt the operation of a plant to the condition required to ensure a high efficiency of the steam ejector. Deviations from the design point mostly result in a reduced efficiency. Limited adaptation of the ejector discharge flow to varying dis-charge pressure requirements is possible by altering the motive steam pressure or by changing the motive steam nozzle dimensions. If the available motive steam pressure is sufficiently high, the dis-charge flow can be adjusted to adapt to different discharge pres-sures by means of a throttling valve in the motive steam line. At low motive steam pressures, it is hardly possible to control motive flow consumption. In such cases, one can employ ejectors with nozzles that have variable cross-sectional areas. An adjustable ejector has an adjustment spindle, which axially extends into the motive steam nozzle and is actuated either manually or by an elec-tric positioner. Mass and volume flow rates of these steam ejectors cover a wider range.

Below figure illustrates the design components of an adjustable ejector and its variable throat.

This geometry consist in inserting a spindle before the primary nozzle and changing its position inside the throat, altering its cross-section area and thus the corresponding area ratio varies accordingly, resulting in the control of the primary mass flow rate. In this way, it is possible for the ejector to work optimally over a range of conditions.