Ejector for ventilation. System of ejector natural ventilation of buildings. Experience in designing natural-mechanical ventilation in residential buildings with warm attics

CALCULATION METHOD OF AN EJECTOR AIR DISTRIBUTOR FOR VENTILATION SYSTEMS IN LIVESTOCK ROOMS

M. M. ACHAPKIN, candidate of technical sciences

It is well known that from the point of view of technical and economic indicators, to ensure optimal microclimatic conditions in livestock buildings, the most acceptable are ventilation systems with air exchange controlled depending on changes in external meteorological conditions. However, the process of regulating air exchange, taking into account the design features of traditional ventilation systems, is a very difficult engineering task.

The solution of this problem is greatly simplified when using ventilation systems for supplying supply air with concentrated jets to the upper zone of the room. In this case, an ejector air distributor (EV) is used as a control device, which is the simplest low-pressure ejector complete with a supply shaft (Fig. 1). The driving force behind the supply air regulation process is

Rice. Fig. 1. Schematic diagram of the operation of an ejector air distributor: 1 - nozzle; 2 - hole for sucked air; 3 - mixing chamber; 4 - supply shaft;

5 - throttle valve

the energy of the air flow coming out of the nozzle.

The essence of the calculation of any engineering and technical means, including EV, is, as you know, in determining its geometric characteristics to ensure the required parameters of the processed medium, depending on the given ones. In our case, in accordance with the theory of development of jets in a closed space, the given parameters are the supply air at the outlet of the mixing chamber. Thus, knowing the required air flow at the outlet of the EV and the cross-sectional area of the livestock building, using the formula presented in , it is possible to determine the diameter of the mixing chamber (the EV supply pipe)

where r^r about - the maximum allowable

reverse air flow rate, m/s;

Lc - second air flow, m3/s;

cross-sectional area of the room, m2.

It is known that in the suction flow ejectors, the movement of flows in the mixing chamber, as well as their mixing, occur due to the kinetic energy of the flow of the working jet flowing from the nozzle. Therefore, for the normal operation of the EV, it is necessary to create at the outlet of the nozzle such a velocity pressure Р\у 12/2, the value of which would be

is equal to (or exceeded) the sum of the required velocity pressure of the suction flow, the velocity pressure on

exit from the mixing chamber, pressure losses in the suction ducts DR2 and in the mixing chamber DR3,

Р3У3 2/2 + Аr2 + Аr3,

where y2, kn is the air velocity in the characteristic sections of the EV, m/s;

Rb R2> Pb - air density in

characteristic sections, kg/m3.

Given the condition of equality of air densities in the characteristic sections of the EV (p\ - P2 - P3) and taking into account that the amount of air at the outlet of the mixing chamber should be equal to

the amount of air at the outlet of the nozzle b\ and on the suction plane 1 ^ 2 s \u003d A + ^ 2)\u003e by simple transformations, one can obtain an approximate value of the air velocity at the outlet of the nozzle:

Taking the free cross section of the suction air flow /2 = ^3 ~ and expressing the values of the flow rates in the characteristic sections through the corresponding velocities and their areas, we find:

In accordance with the data obtained on the theory of mixing flows, the air velocity in characteristic sections is specified and the aerodynamic characteristics of the EV are calculated using well-known formulas, including pressure losses in the suction air outlets DR2 and in the mixing chamber DR3.

It should be noted that it is more convenient to determine the value of the optimal length of the mixing chamber for engineering calculations according to the graph obtained by us on the basis of experimental studies of the dependence of the degree of jet constraint and the length parameter of the mixing chamber

personal values of the mixing factor of the installation (3, shown in Fig. 2.

0,5 1,01,5 2,0 2,53,03,54,04,5 5,0 5,5

Rice. 2. Graph of natural values x\ and *2 for different values of the coefficient

mixing

If the calculation results confirm expression (2) taking into account the pressure margin of the order of 10...15%, then the calculation of the EE can be considered complete.

The process of air exchange regulation is carried out by changing the amount of suction flow depending on the values of the outside air temperature using the throttle valve of the supply shaft.

In accordance with the foregoing, the essence of the methodology for calculating the EV is as follows:

The required air exchange is determined at characteristic values of the outdoor air temperature from ¿„ax to

m1P and according to the formula /3 = b\ calculated

the required mixing ratio of the installation is given;

According to formula (1), the diameter of the mixing chamber (supply pipe) is determined for the case of the maximum air-spirit capacity of the installation;

The geometric and aerodynamic characteristics of the flows in the characteristic sections of the EV are determined. In this case, the air flow rate at the outlet of the nozzle is assumed to be equal to the required air exchange at

The process of air exchange regulation is calculated depending on the values of the outside temperature in the range from ¿„ax to

cooking equipment

air and its supply is selected to ensure the required air exchange

generally accepted method from the condition at

REFERENCES

1. Bakharev V. A., Troyanovsky V. N. Fundamentals 2. Kamenev P. N. Heating and ventilation:

design and calculation of heating and ventilation - At 2 hours 4. 2. Ventilation. Moscow: Stroyizdat, 1966.

tions with a concentrated air outlet. M.: 480 p. Profizdat, 1958. 216 p.

Received 12/25/2000.

SELECTION OF OPERATING MODES OF MACHINE-TRACTOR UNITS WITH THE HELP OF COMPUTER EQUIPMENT

A. M. KARPOV, candidate of technical sciences,

T. V. VASIlkina, Candidate of Mathematical Sciences,

D. A. KARPOV, engineer,

A. V. KOZIN, engineer

It is known that all agricultural operations are carried out by machine-tractor units (MTAs), which are a combination of the power part, the transmission mechanism and the working machine.

Every engineer knows how difficult it is to choose the right power tool and a working (or working) machine in order to obtain high quality, maximum productivity, the lowest specific consumption and the highest value of the coefficient of use of the traction force on the hook, i.e., to maximize the use of traction properties any energy source.

For a long time, such calculations were made manually, which required good engineering knowledge and considerable time.

Specialists had to complete the MTA based on the experience of the previous generation or using reference data. And if the calculations were made, then according to the simplified

diagram, which can be represented as follows:

The range of possible speed mode is set (for a given working machine);

The value of the tractive effort at the selected speeds for these conditions is determined;

The maximum working width of the unit in the selected gears is calculated;

The number of machines (or plow bodies) is determined based on the width of the machine (or plow body);

Find the working resistance;

The degree of tractor loading is calculated by traction force.

Note that the value of the maximum hourly productivity is not determined, and even more so, its verification under production conditions is not carried out. Such a calculation could not but lead to an erroneous decision. In the problem of choosing the optimal energy means for the smallest energy intensity is solved. At the department

To select centrifugal fans, in addition to capacity and pressure, it is necessary to choose their design.

The total pressure Pp developed by the fan is used to overcome the resistance in the suction and discharge air ducts that arise when air moves:

RP = ΔRvs + ΔRn = ΔR,

Where ΔРвс and ΔРн are pressure losses in the suction and discharge air ducts; ΔР is the total pressure loss.

These pressure losses consist of pressure losses due to friction (due to the roughness of the air ducts) and in local resistances (turns, section changes, filters, heaters, etc.).

DR losses (kgf/m2) are determined by summing up pressure losses ΔР, in separate calculated sections:

where ΔРрi and ΔРмсi, respectively, are pressure losses due to friction and in local resistances in the design section of the duct; ΔRud is the pressure loss due to friction per 1 linear meter. m. length; l is the length of the design section of the duct, m; Σζ is the sum of the coefficients of local resistances in the design section; v is the air velocity in the duct, m/s; p is the air density, kg/m3.

The values of ΔRud and ζ are given in reference books.

The procedure for calculating the ventilation network is as follows.

1. Select the network configuration depending on the location of the premises, installations, equipment that the ventilation system must serve.

2. Knowing the required air flow in individual sections of the ducts, their transverse dimensions are determined based on the allowable air speeds (about 6-10 m / s).

3. According to formula (3), the resistance of the network is calculated, and the longest line is taken as the calculated one.

4. According to the catalogs, a fan and an electric motor are selected.

5. If the resistance of the network turned out to be too large, the dimensions of the ducts are increased and the network is recalculated.

Knowing what performance and total pressure the fan should develop, the fan is selected according to its aerodynamic characteristics.

This characteristic of the fan graphically expresses the relationship between the main parameters - performance, pressure, power and efficiency at certain rotation speeds n, rpm. For example, it is required to select a fan with a capacity of L = 6.5 thousand m3/h at P = 44 kgf/m2. For the selected centrifugal fan Ts4-70 No. 6, the required operating mode will correspond to point A (Fig. 8, a). From this point, the speed of rotation of the wheel n - 900 rpm and efficiency η = 0.8 are found.

The most important relationship between pressure and performance is the so-called pressure characteristic of the fan P - L. If this characteristic is superimposed on the network characteristic (dependence of resistance on air flow) (Fig. 8, b), then the intersection point of these curves (operating point) will determine the pressure and fan performance when operating on a given network. If the resistance of the network increases, which can happen, for example, when the filters are clogged, the operating point will shift up and the fan will supply less air than it needs (L2< L1).

When choosing the type and number of centrifugal fans, it is necessary to be guided by the fact that the fan should have the highest efficiency, relatively low rotation speed (u=πDn/60), and also that the wheel rotation speed would allow connection to the electric motor on one shaft.

Rice. Fig. 8. Diagrams for calculating the ventilation network: a - aerodynamic characteristic of the fan; b - fan operation in the network

In cases where the operating fan does not provide the required performance, it can be increased, remembering that the fan performance is directly proportional to the speed of rotation of the wheel, the total pressure is the square of the rotation speed, and the power consumption is the cube of the rotation speed:

A variety of centrifugal fans are the so-called cross-flow fans (see Fig. 7, d). These fans have wide wheels and their performance is higher than that of centrifugal fans, but the efficiency is lower due to the occurrence of internal circulation flows.

The installed power of the electric motor for the fan (kW) is calculated by the formula

where L is the fan capacity, m3/h; P is the total pressure of the fan, kgf/m2; ηv - efficiency of the fan (taken according to

fan characteristics); ηp - efficiency of the drive, which is equal to 0.9 for a flat-belt transmission; with a V-belt - 0.95; with direct installation of the wheel on the motor shaft - 1; when installing the wheel through the clutch - 0.98; k - safety factor (k = 1.05 1.5).

Ejectors are used in exhaust systems in cases where it is necessary to remove a very aggressive environment, dust that can explode not only from impact, but also from friction, or flammable and explosive gases (acetylene, ether, etc.).

Centrifugal fans for transport enterprises are of low (up to 1 kPa), medium (1 ... 3 kPa) and high (3 ... 12 kPa) pressure. In forced ventilation, fans of different pressures are used. The centrifugal type fan contains a spiral-shaped housing, inside which the impeller blades rotate, trapping air in the space between the blades. Under the action of centrifugal forces, the rotating air is pressed against the walls of the housing (housing), is collected inside the housing and is ejected through the outlet. In this case, a vacuum is formed in the center of the wheel, where the outside air rushes; The efficiency of centrifugal fans is 0.7...0.8.

Peculiarities.

The propeller is a pipe with a smoothly pressed end - a nozzle. This pipe is introduced into the suction duct. The principle of operation of the installation is as follows. A jet of air leaving the nozzle at high speed creates a vacuum in the duct (pipe), which enhances the suction of air from the production room. Inside the nozzle, air is supplied through the compressor pipe. The advantages include its fire safety due to the absence of rotating parts and electric motors, which can spark when it hits the rotating parts of metal parts or as a result of loose electrical contact. The disadvantage is the low efficiency of the product - 0.12 ... 0.25. and high tariffs for transportation to the installation site.

At road transport enterprises, running engines of vehicles brought into the premises, dust, gases and vapors released during repair work pollute the atmosphere of the premises. Therefore, in the parking areas, those. maintenance and repair of ZIL vehicles, as well as general ventilation is organized at production sites and in utility rooms.

In addition to the general exchange, local supply and exhaust ventilation systems are provided. Local suctions are supplied to the engine adjustment posts in the area of maintenance and repair of onboard long lengths. Stands for their testing and running-in, devices for checking and baths for washing fuel equipment. Shelves for charging batteries, baths for draining and preparing electrolyte, an oven for heating mastic for batteries, etc. Rooms for oil regeneration, battery charging, spray painting and storage of flammable materials should have separate exhaust ventilation systems.

M. A. Malakhov, Chief Engineer of Mosproekt-2 Projects. M. V. Posokhin

A. E. Savenkov, chief specialist of Mosproekt-2 named after M. V. Posokhin

In recent years, a new name for ventilation in residential buildings has appeared - hybrid ventilation. This implies the use of a known natural ventilation system and a mechanical one without diverter valves. This can be easily implemented in typical houses P-44, etc., which have warm upper technical floors with a temperature of about 14 ºС, obtained due to the heat of the exhaust air coming from the apartments through industrial-made vertical ventilation units (BV-49-1 type) .

The article contains proposals for improving ventilation in residential buildings up to 22 floors in the case of new design and reconstruction of existing buildings with warm attics.

A warm attic is a good collection chamber, from which air is removed to the outside through one common shaft per section.

Such a system was laid down in 1976 in standard designs (at MNIITEP, in the laboratory of M. M. Grudzinsky) and continues to be implemented in new construction.

However, over the years, certain shortcomings of such a system have been revealed due to the fact that new sealed windows are now widely used, through which there is no infiltration in the required volume for standard air exchange in apartments.

Hence the need for special adjustable supply valves, which are installed in the window itself or in the walls. Such dampers (such as "AEREKO" or "ALDES") have become a necessary accessory to improve ventilation without opening the vents, which meets the requirements for protection from street noise and is an effective means of saving heat together with thermostats on heating appliances, which have now become mandatory in the general program saving heat energy in the building. Savings are achieved due to the metered supply of outside air with an increase in relative humidity in the premises. In this case, the valve can have a fixed air flow for a constant minimum air exchange in the absence of people in the apartment.

Picture 1

Calculation scheme of the ejector exhaust unit:

1 - silencer;

2 – axial fan;

3 – flow rectifier;

4 – branch pipe of the ejector;

5 – ejector nozzle;

6 - deflector barrel;

7 - deflector "AS";

8 - transitions;

D 1 - nozzle diameter;

D 2 - nozzle diameter;

D 3 - diameter of the barrel (displacement chamber);

D (L2) is the jet diameter at the distance L2.

The calculation of the scheme is given in the journal "AVOK", No. 6, 2008.

For normal operation of the valve, a pressure drop of about 10 Pa is required, and for this, sufficiently effective exhaust ventilation in the apartment is necessary. In winter, this difference is provided mainly due to the gravitational pressure, with the exception of the upper 2-3 floors, for which the installation of individual household fans is recommended.

In general, in residential 17-storey buildings, natural ventilation functions normally up to a temperature of 5 °C, as provided for by the regulations. To stabilize the hood on all floors in order to be able to install supply valves in Mosproekt-2 named after. M. V. Posokhin proposed a hybrid natural-mechanical exhaust system using a low-pressure ejector and an axial fan in a common exhaust shaft in each section of the house. At the same time, all industrial elements of the building remain (ventilation blocks, a warm attic and a common exhaust shaft).

Figure 2

Scheme of a natural mechanical (ejector) installation with two deflectors for a 22-storey building

This circumstance makes it quite easy to carry out the reconstruction of the ventilation of existing residential buildings, built in large numbers in Moscow and subject to major repairs according to the plan prepared by the government.

Ejector exhaust systems are implemented on the street. Profsoyuznaya, 91 and in building No. 4 on Michurinsky Prospekt. A detailed description of the systems was published in the ABOK magazines (2003, No. 3; 2006, No. 7; 2008, No. 6).

For buildings up to 22 floors (at the above addresses), 2 deflectors with a diameter of 900 mm were installed at a speed in the deflector shaft of 2.5 m/s and a total flow per section of 11,000 m 3 /h (22 floors).

Figure 3

Structural section along the ventilation chamber with two deflectors

The design of this ejector installation is based on natural ventilation up to t out = 5 °C and on the inclusion of an axial fan at t out > 5 °C or, if necessary, according to operating conditions. The ejection coefficient of the installation is assumed to be b = 0.8–1.0, and the fan is assumed to have a capacity of 50–55% of the calculated air flow at a pressure of 170–220 Pa to create ejection. The installed fan power is 1.25 kW per one ejector unit.

It should be noted that the fans must be equipped with step speed controllers, since at an outside temperature below 5 °C, the fan performance doubles due to the gravitational pressure. These data were obtained during testing of systems in building No. 4 on Michurinsky Prospekt (in two sections of 22 floors each).

Figure 4

Proposals for the reconstruction of existing residential buildings with warm attics (17 floors, P-44, etc.)

In general, these tests showed the following:

1. In natural mode, the system works quite satisfactorily.

2. When the fan is turned on, the hood on the top floor is extinguished. The reason for this was the absence of a factory headroom on the technical floor, replaced by a brick box. As a result of a significant increase in speed in the collection channel of the ventilation units, the upper satellite of the unit was drowned out by air. Hence the conclusion: it is imperative to install factory heads and, in addition, from the satellites of the upper floor, take vertical sections up about 1.0 m long, that is, above the heads.

3. AS "Ventstroymontazh" should be installed as deflectors above the shafts, as they showed the best results during measurements.

4. Adjustable exhaust diffusers (for example, DPU-M Arktos) must be installed as exhaust grilles on the satellites of the ventilation units in order to be able to initially adjust the system vertically.

The indicated publications of the AVOK magazine on ejector systems provide a detailed analysis and the necessary calculations that can be used in the design, as well as the necessary data for the selection of equipment for buildings of various heights.

Axial fans of the FE series (Germany) with satisfactory noise characteristics are supplied by KORF.

2. Use inlet slotted or other valves with automatic variable air flow.

3. To control the volume of the hood, you can use the exhaust grills of the firms "AEREKO" or "ALDES"; other adjustable devices are acceptable, for example DPU-M "ARKTOS".

Literature

1. Malakhov M. A. The project of natural mechanical ventilation of a residential building in Moscow / AVOK. - 2003. - No. 3.

2. Malakhov M. A. Systems of natural mechanical ventilation in residential buildings with warm attics /ABOK. - 2006. - No. 7.

3. Malakhov M. A., Savenkov A. E. Experience in designing natural mechanical ventilation in residential buildings with warm attics / ABOK. - 2008. - No. 6.

4. Buttsev B.I. AEREKO in Russia. Ten years later / Prospect.

Mechanical general ventilation can be supply, exhaust and supply and exhaust, with recirculation and without recirculation. With this ventilation system, centrifugal (Fig. 5, a), axial fans (Fig. 5.6) or ejector installations (Fig. 5, c), roof fans (Fig. 5, d, e) move air through air ducts with branches having nozzles and dampers for regulating the inflow or removal of air.

Fans are used in supply, exhaust and supply and exhaust systems, ejector installations - mainly in exhaust ventilation systems.

Ejector installations are used in industrial premises where explosive vapors and gases are released and where the installation of a conventional type fan, which causes sparking and explosion if parts of the fan are damaged, is not allowed, for example, when removing contaminants from battery charging compartments, from painting booths in the absence of hydrotreatment.

Propulsion of air by ejection consists in the fact that one or more nozzles are inserted into the pipe, air is supplied under pressure from a compressor or fan, steam or water, which entrain polluted air. The efficiency of the ejector installation will depend on its design features.

The purpose of supply ventilation systems is to compensate for air removed by local suction and pneumatic transport in workshops and departments (machine, finishing, assembly, chipboard, etc.) and consumed for technological needs.

With a supply general ventilation system (Fig. 6, a), an air inlet for the intake of clean air, which is supplied to the room by a fan, is installed outside the building. The air is taken at a height of at least 2.5 m from the ground. The air in the room, cleaned and heated to the required temperature, is distributed through a system of channels - air ducts.

Air is supplied to the working area (into the space from the floor level to the breathing level of 1.8 ... 2 m) at possibly low speeds. Do not supply air through areas where it is contaminated.

The exhaust general ventilation system (Fig. 6, b) is characterized by the fact that the polluted air is removed by a fan 11 through a network of air ducts 13 and 12. In this case, clean air is sucked in naturally through leaks in doors, windows, lanterns, cracks, pores of building structures. The exhaust vents of the air ducts are located at different heights, which are set depending on the purpose of the premises and the density of the removed contaminants. For example, if pollution is removed that is heavier than air (phenol vapor, gasoline), steam or gas receivers are located near the floor, and if lighter than air, near the ceiling. In accordance with SN 245-71, SNiP P-33-75, GOST 12.4.021-75 and fire regulations, it is not allowed to combine exhausts of easily condensing vapors and gases into one common exhaust unit, as well as exhausts of substances that, when mixed, can create a toxic flammable or explosive mechanical mixture or chemical compounds. For example, it is not allowed to combine suction from pneumatic conveying installations with suction from painting and drying chambers; from painting booths, when nitrocellulose varnishes are used in one of the booths, and polyester varnishes are used in the other. Dusty or polluted with toxic vapors or gases, the air is cleaned and neutralized in special installations before being released into the atmosphere.

The supply and exhaust ventilation system without recirculation (Fig. 6, c) consists of a supply and exhaust system that simultaneously supplies clean air and removes polluted (previously cleaned) air into the atmosphere. Such a ventilation system is considered the best provided that the air removed by the exhaust general and local ventilation systems is compensated by the supply ventilation system.

The supply and exhaust ventilation system in communicating rooms should be designed in such a way as to exclude the possibility of air from rooms with a high emission of harmful substances or with the presence of explosive gases, vapors and dust in rooms where these hazards are less or not.

Recirculation ventilation(Fig. 6, d) is a closed supply and exhaust ventilation. The air sucked out by the exhaust system is re-supplied into the room with the help of supply ventilation. The recirculated air is partially replenished with fresh air. It is not allowed to use recirculation in rooms with toxic fire and explosive air pollution.

In all ventilation systems, the air intake device is installed taking into account the wind rose (on the windward side to the ejected shafts), but not closer than 10 ... 20 m from the ejection openings. The pipe through which the used air is released into the atmosphere must be located at least 1 m above the roof ridge.