External ejector is less than 2 inches. Guidelines for performing calculation and graphic work
course: “Hydrogasdynamics”
on the topic: “Calculation of a gas ejector”
Rybinsk 2005
Scroll symbols 4
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 of a gas ejector 35
2.1 Task 35
2.2 Calculation of operating parameters 35
2.3 Calculation of 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/kgK;
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 quantity 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 working part pipes (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 room ventilation and engine cooling (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. Diagram of the ejector of a steam 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) .
The purpose of the nozzles is to bring gases to the entrance to the mixing chamber with minimal losses. 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 arrangement, 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.
Deep aquifer is a common problem that is familiar to many owners. land plots. Conventional surface pumping equipment either cannot provide the house with water at all, or supplies it to the system too slowly and with low pressure.
This problem needs to be resolved as soon as possible. Agree, buying a new pump is an expensive undertaking and not always financially justified. A solution to this situation can be an ejector for a water supply pumping station.
We will tell you how to choose a suitable unit and install it without the help of specialists. We will also give step-by-step instructions on making and connecting a homemade ejector. All stages of work are supported clear photographs.
The deeper the water is, the more difficult it is to bring it to the surface. In practice, if the well depth is more than seven meters, it has difficulty coping with its tasks.
Of course, for very deep wells it is more appropriate to purchase a high-performance submersible pump. But with the help of an ejector, it is possible to improve the performance of a surface pump to an acceptable level and at significantly lower costs.
The ejector is a small but very effective device. This node has relatively simple design, you can even make it yourself from scrap materials. The operating principle is based on giving the water flow additional acceleration, which will increase the amount of water coming from the source per unit of time.
Image gallery
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 at high speed is transferred to another medium. Thus, the operating principle of an ejector pumping station is based on Bernoulli’s law: if a reduced pressure of one medium is created in a narrowing 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 the compression of a gas medium, initially under low pressure, occurs due to high-pressure gases, are 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 slowed down, 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;
- a nozzle whose cross-section tapers.
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 pumping station such a device as an ejector, keep in mind that the pumped liquid medium enters it not from a well or well, but from a 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 borne in mind that built-in ejectors demonstrate high efficiency 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 emit quite a lot of noise during their operation, so it is recommended to place them in separate room or in a caisson aquifer 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.
- 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 it. 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.
- IN top part tee, which will connect to the suction line of the pump, screw in an adapter with an external thread.
- 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.
- 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.
An ejector is a jet apparatus in which the injection process is carried out, which consists of transferring the kinetic energy of one flow to another flow by direct contact (mixing).
Model:"EZh-2".
Price polyamide: 15,000.00 rub.
Price stainless steel: RUB 25,000.00
Water performance: 2 m 3 /hour.
Air performance: 0.4-0.8 m 3 / hour.
Connecting dimensions of water inlet and outlet: 1".
Connecting dimensions of the gas fitting: 1/2".
How does an ejector work?
The working flow (water) is supplied under pressure into a water-jet ejector to a convergent nozzle. In the nozzle, the water pressure decreases and the speed increases. The jet flowing from the nozzle creates a vacuum in the suction chamber and carries with it the injected medium (gas). To avoid a sharp drop in pressure and speed from the suction chamber to the mixing chamber, a confuser is provided. After passing through the confuser, the flows of two media enter the mixing chamber.
The last element of the ejector is the diffuser - it is designed to increase the pressure of the mixed flow and reduce its speed. At the outlet of the diffuser we have a flow of two mixed media.
Cash upon receipt
Payment in cash is possible upon receipt of the order at the point of issue, in our office or upon delivery by courier service. Please note that some pick-up points do not accept cash payments; the manager will clarify the possibility of payment when confirming the order. If the order amount is more than 30 thousand rubles, an advance payment may be required.
By bank card on the website
If you want to pay for your order online, you need to select the payment method “Card on the website” when placing your order. After confirmation of availability and delivery costs, an email with a link to your personal account will be sent to your email address. To pay for your order, you need to click on the “Pay” button in your personal account, then you will be redirected to the bank’s secure payment page*.
By bank card upon receipt
Payment by bank card is possible upon receipt of the goods at our office and at the delivery points of our partners. Please note that some pick-up points do not accept payment by card; the manager will clarify the possibility of payment when confirming the order.
Cashless payment for individuals. persons
When placing an order, you must select the payment method "Payment by invoice". After confirmation of the order by the manager, an invoice for payment will be sent to your email, which you can pay at any bank that accepts payments from individuals or through online banking.
Cashless payment for legal entities. persons
To receive an invoice for payment, you need to place an order as a legal entity. person and indicate all the data necessary for issuing an invoice (TIN, KPP, company name). Once product availability is confirmed, you will be issued an invoice valid for 3 days.
Loan for up to 24 months or 6 months without overpayment
Opportunity for clients of Sberbank PJSC to issue consumer loan to buy without leaving home. Loan approval through Sbrebank Online. There are 2 lending options available:
- Loan for a period from 3 to 24 months. The total cost of the loan depends on the loan term and the cost of goods.
- For goods marked with the “Credit without overpayment” sticker, you can apply for loan for 6 months with a discount from our company. The discount is calculated in such a way that in the end, with interest, you pay the full cost of the product without overpaying interest on the loan.