Air ejector jet operation steam

Air Jet Ejectors are based on the ejector-venturi principal and operate by passing motive air or gas through an expanding nozzle. The nozzle provides controlled expansion of the motive gas to convert pressure in to velocity which creates a vacuum with in the body chamber to draw in and entrain gases or vapours. The motive gas and suction gas are then completely mixed and then passed through the diffuser or tail, where the gases velocity is converted in to sufficient pressure to meet the predetermined discharge pressure.

Vacuum Ejectors are used in a variety of applications in the process, food, steel and petrochemical industries. Typical duties involve filtration, distillation, absorption, mixing, vacuum packaging, freeze drying, dehysrating and degassing. Ejectors will handle both condensible and none condensible gas loads as well as small amounts of solids or liquids, however accidental entrainment of liquids can cause a momentary interruption in vacuum but this will not cause damage to the ejector.

More recently Air Ejectors have been used for leak testing of under sea pipework, where high levels of vacuum are applied and held on several hundred kilometers of pipe for several days. For these applications several Air Ejectors (either single stage or two stage systems) are used in parallel in reduce the overall duty cycle time.

Ejectors, or jet pumps, utilize the pressure energy of a high-pressure fluid stream to boost the pressure and/or flow of a low-pressure source. They can operate with either incompressible or compressible fluids as the primary (driving) and secondary (driven) flows. The main features of an ejector are shown in Figure 1 . The figure also defines the subscripts used later for primary (1), secondary (2), etc.

The primary fluid is passed through a nozzle where the pressure energy is converted into kinetic energy. The high-velocity jet entrains the secondary fluid. The two streams mix in the mixing tube, leading to pressure recovery. Further static pressure is recovered in a narrow-angle diffuser downstream of the mixing tube.

Ejectors are generally inefficient devices. However, their simplicity and lack of moving parts make them worthy of consideration, particularly where a high-pressure stream of fluid is already available. Table 1 summarizes potential ejector applications.

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