Pumps with remote ejector

In the “Pumps” section we will consider another type of pump - this centrifugal pumps with a remote ejector. Applicable centrifugal pumps with remote ejector, for lifting water from a depth of up to 45 meters from wells or deep wells. Used to create pressure in small systems water supply, as well as for filling containers and reservoirs. The effect of lifting water from such a depth is achieved through the use of a remote ejector. The ejector is lowered into a well or well and connected to the inlet pipes of the pump using two pipes.

Pumps with a remote ejector are used for pumping clean water. Abrasive or any other aggressive liquids can damage the pump. It is also prohibited to use the pump for pumping flammable, combustible or explosive liquids.

Technical characteristics and materials of pumps

Performance characteristics:

The temperature of the pumped liquid is no more than 35° C

Ambient temperature no more than 40° C

Maximum suction depth 45 m.

Noise level in continuous operation no more than 70 dBA

The pump is designed for long-term operation

Engine:

2 pole asynchronous electric motor, number of revolutions 2850 min -1

Insulation class F

Protection class IP 44

Materials:

The pump body is made of cast iron

The impeller is made of plastic (noryl)

The diffuser is made of plastic (noryl)

The remote ejector body is made of cast iron

Venturi tube and remote ejector nozzle are made of plastic (noryl)

The pump shaft is made of stainless steel

Mechanical seal - graphite/ceramic

Operating principle, installation and connection of centrifugal pumps with a remote ejector

The main difference between pumps with a remote ejector and self-priming and normally priming centrifugal pumps is that on the suction side of the pump there are two pipes for connecting two pipelines - supply and return. The supply pipeline, with a diameter of 1 1/4″, supplies water to the pump. The return pipeline recirculates water from the pump to the remote ejector; its diameter is one size smaller than the supply one and is 1″.

Remote ejectors are manufactured in two sizes for four and two inch wells (Fig. 1).

Remote ejector 4″ and 2″

The remote 4″ ejector consists of three parts: body (item 1), nozzle (item 2) and Venturi tube (item 3). The remote 2″ ejector consists of the same main parts as the four-inch one, plus it comes with a special adapter (item 5) for mounting on a well. When installing a remote ejector in a well, it is necessary to install a check valve with a mesh (item 4).

(Fig. 2) shows installation diagrams of centrifugal pumps with a remote ejector for 4″ and 2″ wells.

In four-inch wells, an installation scheme with two pipelines is used. For two-inch wells, a slightly different installation scheme is used. The ejector is mounted on the supply pipeline, and is used as a return pipeline casing. A check valve with a mesh (item 1) must always be installed on the suction pipe of the remote ejector.

The operating principle of pumps with a remote ejector is as follows. Part of the water supplied by the impeller to the pump is directed into the pressure pipeline (item 6), and the rest of the water through the return pipeline (item 4) returns back to the ejector (item 2). Due to water recirculation and the presence of a Venturi tube in the ejector suction chamber, a vacuum is created necessary for sucking water from the well. The amount of water entering the ejector is determined by the diameter of the nozzle. The incoming water is mixed with the recirculating water and the volume of water in the supply pipeline (item 3) increases. Then the process is repeated.

When installing pumps, the following requirements must be observed:

• The pump must be installed in an easily accessible, dry place protected from moisture and frost with the possibility of its inspection, maintenance, repair and replacement.
• The pump is mounted on a level surface horizontal surface, exceeding its size.
• All pipelines supplied to the pumping equipment are installed without tension.
• It is recommended to install the supply and return pipelines with internal diameters corresponding to the suction pipes of the pump. Suction pipelines are installed without unnecessary bends, turns and as short as possible.
• The supply line must be connected so that it rises towards the pump to avoid the formation of air jams. The inclination angle of the supply pipeline should be 1-2° below the pump level.
• Ensure absolute tightness of the supply and return pipelines from the pump to the remote ejector to prevent air leaks and airing of the pump.
• It is imperative to install a mesh on the ejector suction pipe. The suction valve must be lowered into the liquid by at least 30 cm to prevent the formation of a funnel during pump operation.
• It is necessary to install a plug connection as close as possible to the pump, for ease of filling the equipment with water when first starting up. Also provide on the pressure connection shut-off valves, for ease of equipment dismantling.

For normal operation of a pump with a remote ejector, it is necessary that the pump itself, the supply and return pipelines, be constantly filled with the pumped liquid. It is prohibited to put the equipment into operation without filling it with liquid. It is necessary to carefully check the pump itself and the pipelines for leaks; leaky connections lead to air entering the system, and as a result, equipment failure.

For more effective use such a scheme of operation of the water supply system requires constant overpressure to create liquid recirculation, therefore it is recommended to additionally install and in such systems.

Electrical connection of pumps with a remote ejector

The electrical connection must be made by a qualified electrician and in accordance with the Electrical Installation Rules (PUE). When making electrical connections, pay attention to the following:

• The supply voltage must correspond to the operating voltage of the pump indicated on the rating plate.
• The pump must be connected to the power supply using a socket with a grounding wire fed through an equipment protection device (RCD) with a rated leakage current of 30 mA.
• Pumps with a single-phase motor have built-in thermal protection that disconnects the pump from the power supply if the motor overheats.
• For pumps with three-phase motors, it is necessary to additionally install them with a protection current equal to the rated current of the motor.

Schemes electrical connection shown in (Fig. 3)

Electrical connection of pumps with a remote ejector

Operation, maintenance and repair of pumps with a remote ejector

During operation centrifugal pumps with remote ejector do not require special maintenance. During operation, it is necessary to ensure that the pump does not operate without water flow “dry running”. If there is no water, you must immediately disconnect the equipment from the power supply or install dry-running protection to avoid its failure. Find out the reason why the pump does not work and eliminate it.

In conditions where the equipment can be defrosted, it must be dismantled, drained of all liquid, washed clean water and place in a dry place. Before turning the pump back on, you need to check its functionality; to do this, turn the pump on and off for a short time of 1-2 seconds. After installation, fill it with liquid and check for leaks.

In the event of equipment failure, repair the pump only in specialized service centers. When performing equipment repairs, only original spare parts must be used.

To summarize, we can say that when correct operation, pumps with a remote ejector will last a long time and reliably throughout the entire period of use.

Thank you for your attention.

Ejector - what is it? This question often arises among owners country houses and dachas in the process of arrangement autonomous system water supply The source of water entering such a system, as a rule, is a pre-drilled well or well, the liquid from which must not only be raised to the surface, but also transported through a pipeline. To solve such problems, a whole technical complex is used, consisting of a pump, a set of sensors, filters and a water ejector, installed if liquid from the source needs to be pumped out from a depth of more than ten meters.

In what cases is an ejector needed?

Before dealing with the question of what an ejector is, you should find out why a pumping station equipped with it is needed. Essentially, an ejector (or ejector pump) is a device in which the energy of motion of one medium moving with high speed, is transferred to another environment. Thus, the ejector pumping station The operating principle is based on Bernoulli's law: if a reduced pressure of one medium is created in a tapering section of the pipeline, this will cause suction into the formed flow of another medium and its transfer from the suction point.

Everyone knows well: the greater the depth of the source, the harder it is to raise water from it to the surface. As a rule, if the depth of the source is more than seven meters, then a conventional surface pump has difficulty performing its functions. Of course, to solve this problem you can use a more productive submersible pump, but it is better to go the other way and purchase an ejector for a surface-type pumping station, significantly improving the characteristics of the equipment used.

By using a pumping station with an ejector, the liquid pressure in the main pipeline increases, while the energy of the fast flow of the liquid medium flowing through its separate branch is used. Ejectors, as a rule, work in conjunction with jet-type pumps - water-jet, liquid-mercury, steam-mercury and steam-oil.

An ejector for a pumping station is especially relevant if it is necessary to increase the power of an already installed or planned installation of a station with a surface pump. In such cases, the ejector installation allows you to increase the depth of water intake from the reservoir to 20–40 meters.

Overview and operation of a pumping station with an external ejector

Types of ejector devices

According to their design and operating principle, ejector pumps can belong to one of the following categories.

Steam

With the help of such ejector devices, gaseous media are pumped out of confined spaces and a rarefied state of air is maintained. Devices operating on this principle have a wide range of applications.

Steam jet

In such devices, the energy of a steam jet is used to suck gaseous or liquid media from a confined space. Operating principle of the ejector of this type lies in the fact that steam escaping from the nozzle of the installation at high speed carries with it the transported medium exiting through an annular channel located around the nozzle. Ejector pumping stations of this type are used primarily for rapid pumping of water from the premises of ships for various purposes.

Gas

Stations with an ejector of this type, the operating principle of which is based on the fact that compression gas environment, initially under low pressure, occurs due to high-pressure gases, used in the gas industry. The described process takes place in the mixing chamber, from where the flow of the pumped medium is directed to the diffuser, where it is inhibited, and hence the pressure increases.

Design features and principle of operation

The design elements of the remote ejector for the pump are:

• a chamber into which the pumped medium is sucked;
• mixing unit;
• diffuser;
• nozzle, cross section which narrows.

How does any ejector work? As mentioned above, such a device operates according to the Bernoulli principle: if the speed of the flow of a liquid or gaseous medium increases, then an area characterized by low pressure is formed around it, which contributes to the rarefaction effect.

So, the operating principle of a pumping station equipped with an ejector device is as follows:

• The liquid medium pumped by the ejector unit enters the latter through a nozzle, the cross-section of which is smaller than the diameter of the inlet line.
• Passing into the mixer chamber through a nozzle with a decreasing diameter, the flow of the liquid medium acquires a noticeable acceleration, which contributes to the formation of an area with reduced pressure in such a chamber.
• Due to the occurrence of a vacuum effect in the ejector mixer, a liquid medium under higher pressure is sucked into the chamber.

If you decide to equip a pumping station with a device such as an ejector, keep in mind that the pumped liquid medium does not enter it from a well or well, but from the pump. The ejector itself is positioned in such a way that part of the liquid that was pumped out of the well or well by means of a pump is returned to the mixer chamber through a tapering nozzle. The kinetic energy of the liquid flow entering the ejector mixer chamber through its nozzle is transferred to the mass of the liquid medium sucked by the pump from the well or well, thereby ensuring constant acceleration of its movement along the inlet line. Part of the liquid flow, which is pumped out by a pumping station with an ejector, enters the recirculation pipe, and the rest goes into the water supply system served by such a station.

Once you understand how a pumping station equipped with an ejector works, you will understand that it requires less energy to raise water to the surface and transport it through a pipeline. Thus, not only does the efficiency of use increase pumping equipment, but also increases the depth from which the liquid medium can be pumped out. In addition, when using an ejector that sucks up liquid on its own, the pump is protected from running dry.

The design of a pumping station with an ejector includes a tap installed on the recirculation pipe. Using such a valve, which regulates the flow of liquid flowing to the ejector nozzle, you can control the operation of this device.

Types of ejectors at installation site

When purchasing an ejector to equip a pumping station, keep in mind that such a device can be built-in or external. The design and principle of operation of these two types of ejectors are practically no different; the differences are only in the location of their installation. Built-in type ejectors can be placed in inner part pump housing, or be mounted in close proximity to it. The built-in ejection pump has a number of advantages, which include:

• minimum space required for installation;
• good protection of the ejector from contamination;
• there is no need to install additional filters that protect the ejector from insoluble inclusions contained in the pumped liquid.

Meanwhile, it should be kept in mind that high efficiency built-in ejectors are demonstrated if they are used to pump water from sources of shallow depth - up to 10 meters. Another significant disadvantage of pumping stations with built-in ejectors is that they produce quite a lot of noise during their operation, so it is recommended to locate them in a separate room or in a caisson of a water-bearing well. It should also be borne in mind that the design of an ejector of this type involves the use of a more powerful electric motor, which drives the pumping unit itself.

A remote (or external) ejector, as its name suggests, is installed at a certain distance from the pump, and it can be quite large and reach up to fifty meters. Remote-type ejectors, as a rule, are placed directly in the well and connected to the system via a recirculation pipe. A pumping station with a remote ejector also requires the use of a separate storage tank. This tank is necessary to ensure that water is always available for recirculation. The presence of such a tank, in addition, makes it possible to reduce the load on the pump with a remote ejector and reduce the amount of energy required for its operation.

The use of remote-type ejectors, the efficiency of which is slightly lower than that of built-in devices, makes it possible to pump out a liquid medium from wells of considerable depth. In addition, if you make a pumping station with an external ejector, then it can not be placed in the immediate vicinity of the well, but can be mounted at a distance from the water intake source, which can be from 20 to 40 meters. It is important that the location of pumping equipment at such a significant distance from the well will not affect the efficiency of its operation.

Manufacturing an ejector and its connection to pumping equipment

Having understood what an ejector is and having studied the principle of its operation, you will understand that you can make this simple device with your own hands. Why make an ejector with your own hands if you can purchase one without any problems? It's all about saving. Finding drawings from which you can make such a device yourself does not present any particular problems, and to make it you will not need expensive consumables and complex equipment.

How to make an ejector and connect it to the pump? For this purpose you need to prepare the following components:

• tee with internal thread;
• union;
• couplings, elbows and other fitting elements.

The ejector is manufactured according to the following algorithm.

1. A fitting is screwed into the lower part of the tee, and this is done so that the narrow branch pipe of the latter is inside the tee, but does not protrude from its reverse side. The distance from the end of the narrow branch pipe of the fitting to the upper end of the tee should be about two to three millimeters. If the fitting is too long, then the end of its narrow pipe is ground off; if it is short, then it is extended using a polymer tube.
2. IN top part tee, which will connect to the suction line of the pump, screw in an adapter with an external thread.
3. A bend in the form of an angle is screwed into the lower part of the tee with the fitting already installed, which will connect to the recirculation pipe of the ejector.
4. A bend in the form of an angle is also screwed into the side branch pipe of the tee, to which a pipe supplying water from the well is connected using a collet clamp.

All threaded connections, carried out in the manufacture of a homemade ejector, must be sealed, which is ensured by the use of FUM tape. On the pipe through which water will be drawn from the source, a check valve should be placed and strainer, which will protect the ejector from clogging. As pipes with which the ejector will be connected to the pump and storage tank, which ensures water recirculation in the system, you can choose products from both metal-plastic and polyethylene. In the second option, installation does not require collet clamps, but special crimping elements.

If desired, you can arrange the house autonomous water supply almost everywhere. But the main problem is the depth groundwater. If the water surface in the prepared well is at a level of 5-7 meters, then there are no special problems; you can use almost any type of pump that is suitable in terms of performance and power consumption. The situation is different with wells, where the water starts much deeper. In this case, an ejector for a pumping station will be able to cope with the task.

Natural restrictions on work create atmospheric pressure, water column pressure and the strength of the elements of the pumping station itself. To lift water from great depths, it is necessary to use a submersible pump or significantly increase the weight and dimensions of the equipment, from which it simply becomes incapacitated and consumes huge amount energy. To avoid such problems, it is necessary to use additional means to facilitate the rise of water, to push it towards the surface, which is why an ejector is needed.

Operating principle

The ejector is structurally a very simple device. The following main components can be distinguished in its composition:

• nozzle;
• suction chamber;
• mixer;
• diffuser.

The nozzle is a pipe, the end of which has a narrowing. The liquid flowing from the nozzle instantly accelerates, escaping from it at enormous speed. According to Bernoulli's law, fluid flow at high speeds exerts less pressure on environment. A stream of water from the nozzle enters the mixer, where it creates a significant vacuum along its boundaries.

Under the influence of this vacuum, water begins to flow into the mixer from the suction chamber. Next, the combined fluid flow through the diffuser flows further through the pipes.

In fact, in the ejector there is a transfer of kinetic energy from the medium with higher speed to a medium with lower speed. How can this be used in combination with a pump?

The ejector is included in the pipeline running from the well to the pump. Part of the water that rises to the surface returns back to the well to the ejector, forming a recirculation line. Escaping from the nozzle at tremendous speed, it carries with it a new portion of water from the well, providing additional vacuum in the pipeline. As a result, the pump spends less energy to lift liquid from great depths.

By using a valve installed on the recirculation line, you can regulate the amount of water flowing back into the water intake system, thereby adjusting the efficiency of the entire system.

Excess liquid not involved in the recirculation operation is supplied from the pump to the consumer, determining the productivity of the entire station. As a result, you can get by with a smaller engine and a less massive pumping part, which will last longer and consume less energy.

The ejector also makes it easier to start the system; a relatively small volume of water can create sufficient vacuum in the pipeline and initiate the initial intake of water so that the pump does not run idle for a long time.

Design and types of stations

Pumping stations can be equipped with an ejector in two ways. In the first, it is structurally part of the pump and is internal. In the second case, it is implemented as a separate external node. The choice of layout depends on the requirements for the pumping station.

Built-in ejector

In this case, the intake of water for recirculation, as well as the creation of pressure in the ejector, is created in the pump itself. This arrangement makes it possible to reduce the size of the installation.

A pump with an internal ejector is practically not susceptible to the presence of suspended matter in the form of sand and silt. There is no need to necessarily filter the incoming water.

The station is used to collect water from a depth of up to 8 meters. It creates sufficient pressure to supply a large farm, where water is mainly used for irrigation.

The disadvantage of the internal ejector is increased level noise during operation. It is best to install it outside a residential building, preferably in a separate utility room.

The electric motor is obviously selected to be more powerful so that it can also provide the recirculation system. However, this comparison is only relevant in a situation with a well depth of up to 10 meters. At greater depths, pumps with an ejector simply have no alternative, except perhaps submersible type, for which it is necessary to equip a well with a large diameter.

Remote ejector

With a remote ejector device, an additional tank is installed separately from the pump, into which water flows. It creates the necessary pressure for operation and additional vacuum to lighten the load of the pump. The ejector itself is connected in the submersible part of the pipeline. For it to work, it is necessary to lay two pipes into the well, which imposes some restrictions on the minimum permissible diameter.

This constructive solution reduces the efficiency of the system to 30-35%, but allows water to be extracted from deep wells up to 50 meters, and also significantly reduces the noise of an operating pumping station.

It can be located directly in the house, for example in the basement. The distance from the well can be up to 20-40 meters without reducing efficiency. Such characteristics determine the popularity of pumps with an external ejector. All equipment is located in one prepared place, which increases the service life and makes it easier to perform preventive work and configure the system.

Connection

In the case of an internal ejector, if it is included in the design of the pump itself, installation of the system is not much different from the installation of a non-ejector pump. It is enough to simply connect the pipeline from the well to the suction inlet of the pump and arrange a pressure line with associated equipment in the form of a hydraulic accumulator and automation that will control the operation of the system.

For pumps with an internal ejector, in which it is fixed separately, as well as for systems with an external ejector, two additional stages are added:

• An additional pipe is laid for recirculation from the pressure line of the pumping station to the ejector inlet. The main pipe from it is connected to the pump suction.
• A pipe with check valve and a coarse filter for drawing water from a well.

If necessary, a valve is installed in the recirculation line for adjustment. This is especially beneficial if the water level in the well is much higher than the pumping station is designed for. You can reduce the pressure into the ejector and thereby increase the pressure in the water supply system. Some models have a built-in valve for such a setting. Its placement and adjustment method are indicated in the equipment instructions.

course: “Hydrogasdynamics”

on the topic: “Calculation of a gas ejector”

Rybinsk 2005

Scroll symbols 4

1 Theoretical information 5

1.1 Purpose and diagrams of ejectors 5

1.2 Working process of ejector 9

1.3 Calculation of gas ejector 18

1.4 Approximate formulas for calculating the ejector 31

2 Calculation example for a gas ejector 35

2.1 Task 35

2.2 Calculation of operating parameters 35

2.3 Calculation geometric parameters 38

3. Task options 40

References 42

List of symbols

P - pressure, Pa;

n – ejection coefficient;

w – speed, m/s;

G – gas consumption, kg/s;

Q – heat flow, W;

E – kinetic energy of gas, J;

Kinetic energy loss, J;

- the ratio of the areas of the outlet sections of the nozzles for the ejecting and ejected gases;

f – degree of expansion of the diffuser;

σ D – total pressure conservation coefficient;

 - temperature ratio of the ejected and ejecting flows;

с р – heat capacity of gas, J/kgK;

T - gas temperature, K;

F – area, m2;

 - reduced flow velocity;

 0 – ratio of the total pressure of the ejecting gas to the total pressure of the ejected gas;

k is the adiabatic index.

Subscripts

1 – parameter of the ejected gas;

2 – ejecting gas parameter;

3 – gas mixture parameter;

kr – parameter in the critical section;

Superscripts

* - braking parameter.

1 Theoretical information

1.1 Purpose and diagrams of ejectors

A gas ejector is a device in which the total pressure of a gas flow increases under the influence of a jet of another, higher-pressure flow. The transfer of energy from one flow to another occurs through their turbulent mixing. The ejector is simple in design, can operate in a wide range of gas parameters, allows you to easily adjust the work process and switch from one operating mode to another. Therefore, ejectors are widely used in various areas technology. Depending on the purpose, ejectors are made in different ways.

Rice. 1. Diagram of a wind tunnel with an ejector: 1 - compressed air cylinder, 2 - ejector, 3 - working part of the pipe.

So, in the one shown in Fig. 1 in the wind tunnel diagram, the ejector plays the role of a pump, allowing a large amount of gas to be supplied at a relatively low cost. high pressure due to the energy of a small amount of high pressure gas. The cylinder (1) contains air at a higher pressure than is necessary for the pipe to operate. However, the amount of compressed air is small, and to ensure sufficiently long operation of the pipe, compressed air is released into the ejector (2), where atmospheric air is mixed with it, which is sucked in by the ejector through the working part of the pipe (3). The greater the pressure of compressed air, the greater the amount of atmospheric air that can be set in motion at a given speed. Often an ejector is used to maintain a continuous flow of air in a duct or room and thus acts as a fan. An example is the diagram of a jet engine test bench shown in Fig. 2. The jet of exhaust gases flowing from the jet nozzle sucks air from the shaft (1) into the ejector (3), thereby providing ventilation of the room and cooling of the engine (2). In this case, hot gases are mixed with atmospheric air, which reduces the temperature of the gas in the exhaust shaft (4) and improves the operating conditions of exhaust devices (silencers, etc.).

Rice. 2. Diagram of a stand for testing turbojet engines: 1 - inlet shaft, 2 - engine on a balancing machine, 3 - ejector, 4 - exhaust shaft.

In many cases, the ejector is used as an exhauster to create reduced pressure in a certain volume. This is, for example, the purpose of an ejector in condensation systems of steam power plants. To increase the power of a steam engine or turbine, it is necessary to maintain as low a pressure as possible in the condenser where the exhaust steam is released. The ejector (Fig. 3) creates the necessary vacuum due to the fact that the steam and air particles in the condenser are picked up and carried away by a high-pressure jet of steam or water. In vacuum technology, ejectors of a similar design, operating on mercury vapor, are used to create a deep vacuum of the order of millionths of the atmosphere.

An example of successful use of the properties of ejectors is their use in gas collection networks. Natural gas sources (wells) located in the same area can produce gas at different pressures. If you simply connect them to a common line, then the pressure in the line must be reduced somewhat below the pressure of the lowest pressure source. In this case, the gas flow rate from low-pressure wells will be small due to the small pressure drop, and the energy of gas pressure from high-pressure wells will be wasted when it expands (throttles) to the pressure in the common pipeline. To effectively use all sources, it is advisable to connect low-pressure wells to the main line using an ejector, in which the pressure of low-pressure gas increases due to the energy of some of the gas from high-pressure wells. The ejector in this case is a compressor. In this way, it is possible to simultaneously increase the gas pressure in the pipeline, increase the productivity of low-pressure wells and connect to the network such gas sources that, due to low pressure, are unprofitable to use when simply integrated into a common network.

Rice. 3. Steam ejector diagram condensing unit: 1 - high pressure steam, 2 - steam from the condenser.

Below we will consider another possible area of ​​using the properties of the ejector, namely, increasing jet thrust by mixing external air with the gas stream flowing from the jet engine nozzle.

Regardless of the purpose of the ejector, it always contains the following structural elements: a high-pressure (ejecting) gas nozzle (1), a low-pressure (ejecting) gas nozzle (2), a mixing chamber (3) and, usually, a diffuser (4) (Fig. 4) .

Purpose of nozzles - with minimal losses bring gases to the entrance to the mixing chamber. The location of the nozzles can be as in Fig. 4 (the ejecting flow is inside, and the ejected flow is along the periphery of the chamber), and reverse (Fig. 1), when the ejecting gas is supplied to the chamber through the outer annular nozzle. To reduce the length of the mixing chamber, one or both streams can be divided into several jets, which requires a corresponding increase in the number of nozzles. Mutual position, the number and shape of nozzles do not, however, have a significant effect on the final parameters of the gas mixture. What is important is only the ratio between the cross-sectional values ​​of the flows of ejected and ejecting gases at the entrance to the chamber, i.e., the ratio of the total areas of the nozzles.

If the pressure drop in the ejecting gas nozzle significantly exceeds the critical value, then in some cases it is advantageous to use a supersonic nozzle. At the same time, the parameters of the ejector in the design mode can be improved.

However, even at high supercritical pressure ratios, it is possible to use an ejector with a non-expanding nozzle, in which the flow rate of the ejecting gas does not exceed the speed of sound. Such an ejector is usually called a sonic ejector. This is the most common type of ejector, operating effectively over a wide range of gas parameters.

Rice. 4. Schematic diagram of the ejector: 1 - ejecting gas nozzle, 2 - ejected gas nozzle, 3 - mixing chamber, 4 - diffuser.

The mixing chamber can be cylindrical or have a cross-sectional area that varies along its length. The shape of the chamber has a noticeable effect on the mixing of gases. Therefore, although below we will mainly consider ejectors with a cylindrical mixing chamber, we will also talk about the principle of calculating ejectors with a chamber of variable cross-section.

The length of the chamber is chosen such that the process of mixing flows practically ends in it, but as short as possible, so as not to increase hydraulic losses and reduce the overall dimensions of the ejector.

In the ejector shown in Fig. 4, the outlet cross-section of the nozzles coincides with the inlet cross-section of the cylindrical mixing chamber. Existing methods for calculating an ejector are designed specifically for such a scheme, so it will be considered further. However, in practice, the nozzles are often located at some distance from the inlet section of the chamber. So, for example, the engine nozzle on the stand (Fig. 2) cannot be placed in the inlet section of the cylindrical chamber of the ejector, since the vacuum existing in this section will change the distribution of Pressure on the outer surface of the nozzle, which will introduce an error in the value of the measured jet thrust. The diffuser is installed at the outlet of the mixing chamber in cases where it is desirable to increase the static pressure of the gas mixture at the outlet of the ejector or when, at a given outlet pressure, it is desirable to obtain a low static pressure in the mixing chamber and in the inlet section of the ejector.

It should be noted that the ejector can operate without a diffuser. In this case, the final cross-section of the mixing chamber is simultaneously the outlet cross-section of the ejector. Sometimes, instead of a diffuser, a tapering or Laval nozzle is installed at the outlet of the mixing chamber. This may be appropriate when the ultimate goal is to accelerate the gas flow after mixing. For example, in various designs of bypass jet engines, gas flows emerging from the circuits are mixed in a common chamber and then flow into the atmosphere through a common subsonic or supersonic jet nozzle.