Steam jet pump principle

Steam jet pumps rely on high-speed steam jet from the Laval nozzle to carry gas, it has the following characteristics:
(1) The pump has no mechanical movement and is not restricted by the conditions of friction, lubrication and vibration. Therefore, the pump can be made with high pumping capacity. Reliable work, long service life. As long as the appropriate choice of structural materials pump for the exclusion of corrosive gases, gas containing mechanical impurities and water vapor and other occasions extremely favorable.
(2) Simple structure, light weight, small footprint. (3) working steam pressure of 4 ~ 9 × 105Pa, in the general metallurgical, chemical, pharmaceutical and other enterprises have such a source of water vapor.
First, the steam jet pump 1. Overview Steam jet pumps rely on the high-velocity steam flow from the Laval nozzle to carry gas, so the following features:
(1) The pump has no mechanical movement and is not restricted by the conditions of friction, lubrication and vibration. Therefore, the pump can be made with high pumping capacity. Reliable work, long service life. As long as the appropriate choice of structural materials pump for the exclusion of corrosive gases, gas containing mechanical impurities and water vapor and other occasions extremely favorable.
(2) Simple structure, light weight, small footprint. (3) working steam pressure of 4 ~ 9 × 105Pa, in the general metallurgical, chemical, pharmaceutical and other enterprises have such a source of water vapor.
Because of the above characteristics of steam jet pump, it is widely used in metallurgical, chemical, pharmaceutical, petroleum and food industries.
2. Working principle Jet pump is composed of working nozzle and diffuser and mixing chamber. Working nozzle and diffuser these two components form a special section of gas flow pipe changes. Air flow through the nozzle can be pressure energy into kinetic energy. The pressure difference between the working vapor pressure P0 and the pump outlet pressure P4 causes the working steam to flow in the pipe.
In this particular pipe, steam passes through the nozzle outlet to this area (mixing chamber) between the diffuser inlet and a negative pressure area appears due to the high velocity of the steam flow. The negative pressure here is much lower than the working vapor pressure P0 and backpressure P4. At this moment, the sucked gas is sucked into the mixing chamber, the working steam and the sucked gas are intermixed with each other for energy exchange, the working steam is transferred to the sucked gas by the kinetic energy transformed by the pressure energy, the mixed gas flow is diffused in a certain section A positive shock wave is generated. The mixed gas flow velocity after wave is reduced to subsonic ω3 and the pressure of the mixed gas flow is increased to P3. Subsonic airflow is decelerated and pressurized while the diffuser is expanding. Mixed gas flow in the diffuser exit, the pressure increased to P4, the speed dropped to ω4. Jet pump is also a gas compressor.
3. Multi-stage jet pump structure usually single stage ejector compression ratio does not exceed 10, the working pressure is not less than lOkPa. So when the need for lower working pressure, then by two or more ejectors and condensers in series, called multi-stage jet pump. The role of the condenser is to condense the condensable steam in the mixture partially to eliminate the load of the lower ejector. The structure of the condenser are hybrid, surface and jet three forms. Condenser according to its injection pump system in the installation location, is divided into the front condenser, the middle condenser and the rear condenser.
The front condenser is installed in front of the primary ejector inlet, primarily to reduce the load on the primary pump. Only when the pumping mixture contains a large amount of condensable steam, and the steam partial pressure stronger than the cooling water temperature corresponding to the saturated vapor pressure can only be used. Intermediate condenser installed in the middle of the multi-stage pump, the specific location should be depending on the mixture into the condenser steam partial pressure and cooling water temperature, and its role is to reduce the load on the lower pump. After the rear condenser is installed in the final stage ejector, mainly to eliminate the final ejector exhaust, noise, and sometimes used to recover the exhaust heat of the non-stage ejector.
4. Simple calculation (1) Calculation of nozzle throat diameter D0 (1) Where G0 - working steam consumption (kg / h), G0 = Gh / μ. Gh is the volume of gas being drawn (kg / h), μ is the emissivity coefficient.
P0 - working steam pressure (Pa)
(2) Calculation of diffuser throat diameter D3 (2) where GK - air flow through the diffuser throat (kg / h)
GZ - Vapor flow through diffuser throat (kg / h)
P4 - diffuser outlet pressure (Pa)
(3) Calculation of condenser diameter D (3) where GΣh - mixture flow into the condenser (kg / h)
vΣh - The specific volume of the mixture entering the condenser (m3 / kg), which can be approximated by the specific volume of saturated water vapor detected by P4.

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