Working principle of steam jet pumps

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I. Overview of Steam Jet Pumps A steam jet pump uses a high-speed stream of steam ejected from a Laval nozzle to carry gas, and therefore has the following characteristics: 1. This type of pump has no mechanical moving parts, and it is not affected by factors such as friction, lubrication, or vibration; as a result, it can be designed to have a very high pumping capacity. Reliable in operation and has a long service life. As long as the structural materials of the pump are chosen appropriately, it is highly advantageous for removing gases with corrosive properties, gases containing mechanical impurities, as well as water vapor. 　　2. It has a simple structure, is lightweight, and occupies little space. 　　3. The working steam pressure is 4–9×105 Pa, and such a source of steam is available in most metallurgical, chemical, pharmaceutical, and other types of enterprises. 　　Due to the aforementioned characteristics, steam jet pumps are widely used in industrial sectors such as metallurgy, chemicals, pharmaceuticals, petroleum, and food processing. II. Working principle of the steam jet pump A jet pump is composed of a working nozzle, a diffuser, and a mixing chamber connected together. The working nozzle and the diffuser together form a special airflow duct with a varying cross-section. Air flow passing through a nozzle can convert pressure energy into kinetic energy. The pressure difference between the working steam pressure P0 and the pump’s outlet pressure P4 drives the working steam to flow through the pipeline. Figure 1: Schematic diagram of the working principle of a steam jet pump. In this special pipe, steam passes through the area between the nozzle outlet and the diffuser inlet (the mixing chamber); due to the high speed of the steam flow, a region of negative pressure is created. The negative pressure here is much lower than the working steam pressure P0 and the backpressure P4. At this point, the gas to be evacuated is drawn into the mixing chamber, where the working steam and the gas to be evacuated mix with each other and exchange energy; the kinetic energy of the working steam, derived from its pressure energy, is transferred to the gas to be evacuated. The mixed flow generates a normal shock wave at a certain section in the expansion section of the diffuser (as shown at section 3’ in Figure 1). Behind the shock wave, the velocity of the mixed flow decreases to subsonic levels, ω’3, while its pressure rises to P’3. Subsonic airflow slows down and experiences an increase in pressure as it flows through the diverging section of the diffuser. At the exit of the diffuser, the pressure of the mixed gas stream increases to P4, and its velocity decreases to ω4. Therefore, a jet pump is also a gas compressor.