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What is a steam ejector? How does it work?

2022-02-17


Steam ejector is a kind of equipment that uses high-pressure fluid (called working fluid) to inhale low-pressure fluid (called injection fluid) to increase the pressure of injection fluid, with simple structure, stable structure, low operating cost and wide application. Examples include vacuum systems, cooling cycles, chemical industry, rocket and jet propulsion systems, core cooling systems for nuclear power plants, etc.
  
A steam ejector is a type of ejector that uses steam as the working fluid. Although various application-specific steam ejectors pursue different purposes (e.g. steam jet vacuum pumps require a maximum injection coefficient at a specific injection pressure, or a minimum injection vacuum when a specific injection medium flow rate is required). Steam jet heat pumps require a maximum compression ratio that can be obtained at a specific operating pressure or workload, but the basic operating principle is the same. That is to say, the working steam accelerates to form a supersonic jet in the Laval nozzle, and the injection fluid is sucked into the mixing chamber due to the shear action with the working steam, gradually forming a single uniform mixed fluid, which is decelerated and compressed to a certain back pressure by the diffusion section and then discharged from the injector.
  
A steam ejector is an energy conversion device. It is a working fluid with a certain amount of energy (pressure and flow), which converts static pressure energy into kinetic energy and ejects it through the nozzle to form a high-speed jet. Due to the entrainment and turbulent diffusion between the jet and the air, the gas in the sucked chamber is carried away, resulting in a local vacuum state, and the sucked fluid enters the pump chamber under the action of external atmospheric pressure. Accompanied by high-pressure and high-speed fluids, it is brought into the throat, mixed with it and exchanged energy. In the throat, due to the turbulence of gas molecules, the working fluid transfers a part of kinetic energy and heat energy to the sucked fluid, so that the kinetic energy and thermal energy of the sucked fluid are enhanced, the speed of the working fluid is slowed down, and the speed of the sucked fluid is gradually accelerated. At the end of the throat, the two streams of fluid gradually converge and mix into the diffusion chamber, and then the flow rate gradually decreases and the pressure rises. Medium quality steam is completed for further applications.
  
The working process of a steam ejector can be roughly divided into three stages:
  
(1) The working fluid can form a high-speed jet to convert pressure into kinetic energy stages.
  
(2) In the mixing stage of working fluid and injector, the two fluids exchange mass, momentum and energy, the speed of the injector increases, and the working fluid transports the ejector to the diffusion section.
  
(3) Compression stage, that is, the two fluids in the expander gradually compress while continuing the energy exchange, converting kinetic energy into pressure energy, and the mixed fluid is discharged from the ejector.
  
Scope of use
  
1. High temperature and high pressure steam with high energy attracts low-pressure steam by jetting high-speed jets, which is used for steam with mixed temperature and pressure required by the production process. This is a more energy-efficient form (as opposed to a temperature and pressure reducer) required to solve the process, and it is also more convenient.
  
2. Attract a certain amount of cold water to the required temperature through the steam jet and send it to the necessary place for heating and domestic water.

 

 

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