Special lecture on mechanical equipment: “Pumps” – Learn a little every day (12): Jet vacuum pumps “Improve yourself””

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This post was last edited by A’dai Amu on 2013-12-12 at 12:31. In order to encourage more people to participate in discussions and to study more actively, the top five users each time will receive a “Motivation Reward for Active Learning”. Some people might think that it’s terrifying to spend their working days doing nothing, performing menial tasks without knowing what to do or what to learn, day after day, year after year, with no vision for their future! We must start working hard from now on; even if we learn a little knowledge every day, it will add up over time and help us enrich ourselves. We need to set clear goals – only by filling our minds first can we enrich other aspects of our lives as well. . . . . . Just spend a short ten-odd minutes every day, and you will see the future! ! ! (Anyway, I have learned it; whether you learn it or not is up to you. Besides those experts like Hai Chuan, there are still others who know it.) . . ) Enough talk – let’s start with the basics today!! I’ve been posting special threads for so many days now; I’m sure everyone has benefited a lot from them. Thank you all for your support~~! Welcome everyone to listen. I have started broadcasting, and I hope those who, like me, want to gain knowledge every day will listen. Let’s learn together every day and discuss~~! These past few days, many people have asked questions, and I’ll do my best to answer them all. There might be some I’ve never encountered before, but there are still plenty of people in our community who can help answer them. @AidaiAmu @hcwang12345 @YiHuXiangMing @tjdxz @YouDianDai @NewbiesPlayingHaiChuan @lovestory @ManTianYun @zhaoqingsheng Yesterday we used a car pump, and I believe the members here now have a basic understanding of car pumps!! A friend from the marine community told me that I talk too much every day; in the future I’ll try to present the information in more detailed forms, in smaller amounts, to make it easier for everyone to learn*~~! Today, I’ll explain jet vacuum pumps to everyone. Come on, let’s learn about it~~! Jet vacuum pump: A vacuum pump that uses a water vapor jet for evacuation, also known as a jet pump. The characteristics of jet pumps are: fast activation, a wide operating pressure range, high pumping capacity, the ability to discharge directly into the atmosphere, a simple structure, reliable operation due to the absence of moving parts, and a long service life. This type of pump is well suited for pumping dusty, condensable, corrosive, and flammable gases. However, this type of pump consumes a large amount of steam and water, with a low efficiency; therefore it is suitable for applications where there is inexpensive by-product steam or available excess/waste steam. Jet pumps are widely used in vacuum smelting, vacuum degassing, vacuum concentration, vacuum drying, vacuum distillation, vacuum refrigeration, and vacuum transportation. A water vapor jet vacuum pump is essentially composed of a ejector and a condenser. A jet pump that consists of a single ejector is called a single-stage pump, while a jet pump made up of two or more ejectors connected in series is referred to as a 2-stage pump, 3-stage pump, etc. (See the table on the performance of jet pumps for a schematic diagram of the ejector’s structure and its working principle.) A working steam stream with pressure ρ0 and velocity ω0 flows through a Laval nozzle (see Laval nozzles); at the outlet of the nozzle, the velocity of the jet increases to supersonic levels of ω1, while the pressure drops to ρ1. This causes the gas to be drawn in, where it collides with the high-velocity steam stream, mixes with it, exchanges energy, and then moves toward the diffuser. In the converging section of the diffuser, the steam and the gas to be pumped are further mixed to form a uniformly mixed gas. During this process, the velocity of the mixture gas begins to decrease continuously, while the pressure increases continuously, resulting in the formation of a positive shock wave near the throat section of the diffuser. The velocity of the mixed gas drops sharply from supersonic to subsonic, while the pressure rises sharply as a result. At the outlet of the diffuser, when the pressure rises to atmospheric pressure or the inlet pressure of the next stage injector, the mixed gas is discharged. In multi-stage pumps, the compression ratio of a single-stage jet pump (i.e., the ratio of discharge pressure to intake pressure) is generally no more than 10; to achieve lower ultimate pressures, multi-stage pumps are used. Table: Performance of jet pumps shows the performance of jet pumps with different stages. The mixed gas ejected by each ejector in a multi-stage pump is a mixture of the gas to be pumped and the working steam; except for that from the last stage which is discharged into the atmosphere, all of it is drawn away by the subsequent stage, which increases the load on that subsequent stage or deteriorates the performance of the pump. Therefore, multi-stage pumps often have an intermediate condenser installed between the two stages of ejectors, so that most of the condensable gases in the mixed gas can be condensed. If the gas to be extracted contains a large amount of condensable gases, and its partial pressure is much higher than the saturated vapor pressure at the condenser inlet temperature, then a first-stage condenser is installed at the inlet of the first stage. To recover the residual heat of the final-stage mixed gas and eliminate airflow noise, a final-stage condenser can be installed. The structures of condensers include mixed type, surface type, and jet type, etc., which can be selected according to different circumstances and requirements during design. For injectors with a working pressure of less than 700 Pa, due to the high steam expansion ratio (the ratio of steam pressure at the nozzle inlet to that at the outlet), the temperature at the outlet is below 0°C; therefore, to prevent frosting, a heating jacket must be installed on the converging section of the diffuser. The installation height of the ejector pump equipped with a mixed-type condenser is above 11 meters; this is to enable the return water from the condenser to be discharged outside the pump due to its own weight, thereby maintaining the pump’s seal. This type of pump is called an elevated vacuum pump. To reduce civil engineering costs, using a water pump to draw out the return water can lower the installation height; such pumps are known as low-mounted vacuum pumps. The reliability of submersible pumps is affected by the water pump, and moreover, maintenance costs increase, so they are generally not used. Selection of working steam: Using high-pressure steam enables a larger expansion ratio; the ejector has a higher entrainment coefficient (the weight ratio of the gas to be pumped to that of the working steam), which reduces the steam consumption and cooling water required by the pump. However, when the pressure exceeds 1.2 MPa, the effect becomes insignificant, and it also increases the cost of producing steam. Steam with a pressure of 0.4 to 1 MPa is usually selected; steam at as low as 0.25 MPa can also be used. In ejectors that operate in a high vacuum at working pressures below 100 Pascals, if steam at such high pressure is used, a large expansion ratio of the steam is required to achieve exhaust functionality, which is difficult to accomplish; therefore, steam with lower pressure (0.05–0.1 MPa) is usually chosen. The performance of wet steam pumps is unstable; therefore, dry saturated steam or superheated steam is generally used. After watching the lecture, have you also gained an understanding of jet vacuum pumps? Come on, learn a little knowledge every day to enrich yourself; little by little, it all adds up to something great~~~! Below are my special series of lectures on mechanical equipment – “Pumps”. Learn something new every day: (16) Pneumatic diaphragm pumps – “Improve your knowledge” http://bbs.hcbbs.com/thread-1257985-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (15) Pneumatic diaphragm pumps – “Improve your knowledge” http://bbs.hcbbs.com/thread-1257433-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (14) Mixed-flow pumps – “Improve your knowledge” http://bbs.hcbbs.com/thread-1257224-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (13) Axial flow pumps – “Improve your knowledge” http://bbs.hcbbs.com/thread-1256970-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (12) Jet vacuum pumps – “Improve your knowledge” http://bbs.hcbbs.com/thread-1256707-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (11) Automotive pumps – “Improve your knowledge” http://bbs.hcbbs.com/thread-1256253-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (10) Pump materials – “Improve your knowledge” http://bbs.hcbbs.com/thread-1255790-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (9) Self-priming pumps and pump materials – “Improve your knowledge” http://bbs.hcbbs.com/thread-1255635-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (8) Oil seals – “Improve your knowledge” http://bbs.hcbbs.com/thread-1255340-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (7) Seals – “Improve your knowledge” http://bbs.hcbbs.com/thread-1255132-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (6) O-rings – “Improve your knowledge” http://bbs.hcbbs.com/thread-1254912-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (5) Pump structure – “Improve your knowledge” http://bbs.hcbbs.com/thread-1254630-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (4) Pump structure – “Improve your knowledge” http://bbs.hcbbs.com/thread-1254625-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (3) – “Improve your knowledge” http://bbs.hcbbs.com/thread-1253809-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (2) Schematic diagram of centrifugal pumps – “Improve your knowledge” http://bbs.hcbbs.com/thread-1253590-1-1.html. Lectures on mechanical equipment – “Pumps”: Learn something new every day (1) Pump selection – “Improve your knowledge”. These are my special posts; I will continue to update them daily. Please give me your support, listen, and discuss ； If there’s any direction that needs to be explained, feel free to contact me. If many people ask for it, I’ll create a dedicated post to cover it~~! :) A series of special lectures on mechanical equipment titled “Pumps” – a summary post featuring new knowledge each day, continuously updated at http://bbs.hcbbs.com/thread-1256318-1-1.html. Everyone is welcome to listen; I’ve already started broadcasting these lectures, and I hope those who, like me, want to gain knowledge every day will listen as well. Let’s learn together every day and discuss~~!