All devices, regardless of their purpose, are designed to create a flow of air (pure or containing impurities of other gases or small homogeneous particles) of different pressures. The equipment is divided into classes for creating low, medium and high pressure.

The units are called centrifugal (and also radial) because of the way air flow is created by rotating a radial blade-type impeller (drum or cylinder shape) inside a volute chamber. The blade profile can be straight, curved, or “wing profile”. Depending on the rotation speed, type and number of blades, the air flow pressure can vary from 0.1 to 12 kPa. Rotation in one direction removes gas mixtures, in the opposite direction it injects fresh air into the room. You can change the rotation using a rocker switch, which changes the phases of the current at the terminals of the electric motor.

Equipment housing general purpose for work in non-aggressive gas mixtures (clean or smoky air, particle content less than 0.1 g/m3) is made of carbon or galvanized steel sheets of various thicknesses. For more aggressive gas mixtures (active gases or vapors of acids and alkalis are present), corrosion-resistant (stainless) steels are used. Such equipment can operate at ambient temperatures up to 200 degrees Celsius. In the manufacture of an explosion-proof version for work in hazardous conditions (mining equipment, high content of explosive dust), more ductile metals (copper) and aluminum alloys are used. Equipment for explosive conditions is characterized by increased massiveness and eliminates sparking during operation ( main reason explosions of dust and gases).

Drum ( Working wheel) with blades is made of steel grades that are not subject to corrosion and are sufficiently ductile to withstand prolonged vibration loads. The shape and number of blades are designed based on aerodynamic loads at a certain rotation speed. A large number of blades, straight or slightly curved, rotating at high speed, create a more stable air flow and produce less noise. But the air flow pressure is still lower than that of the drum on which blades with an aerodynamic “wing profile” are installed.

“Snail” refers to equipment with increased vibration, the reasons for which are precisely the low level of balance of the rotating impeller. Vibration causes two consequences: increased noise levels and destruction of the base on which the unit is installed. Shock-absorbing springs, which are inserted between the base of the housing and the installation site, help reduce vibration levels. When installing some models, rubber cushions are used instead of springs.

Ventilation units - “snail” are equipped with electric motors, which can be equipped with explosion-proof housings and covers, improved painting for operation in aggressive gas environments. Mainly asynchronous motors with a certain rotation speed. Electric motors are designed to operate from a single-phase network (220 V) or three-phase (380 V). (Power single-phase electric motors does not exceed 5 - 6 kW). In exceptional cases, a motor with controlled rotation speed and thyristor control can be installed.

There are three ways to connect the electric motor to the drum shaft:

1. Direct connection. The shafts are connected using a keyed bushing. "Constructive diagram No. 1."
2. Through a gearbox. The gearbox can have several gears. "Constructive diagram No. 3."
3. Belt - pulley transmission. The rotation speed may change if the pulleys are changed. "Constructive diagram No. 5."

The safest connection for an electric motor in case of sudden jamming is a belt-pulley connection (if the impeller shaft suddenly and abruptly stops, the belts will be damaged).

The casing is manufactured in 8 positions of the outlet hole relative to the vertical, from 0 to 315 at 45 degrees. This makes it easier to attach the unit to the air duct. To eliminate the transmission of vibration, the flanges of the air duct and the unit body are connected through a sleeve made of thick rubberized tarpaulin or synthetic fabric.

The equipment is painted durable powder paints with increased impact resistance.

Popular VR and CC models

1. Fan VR 80 75 low pressure

Designed for industrial and industrial ventilation systems public buildings. Working conditions: temperate and subtropical climate, in non-aggressive conditions. The temperature range suitable for operation of general purpose equipment (GP) is from -40 to +40. Heat-resistant models can withstand increases up to +200. Material: carbon steel. Average humidity level: 30-40%. Smoke collectors can operate for 1.5 hours at a temperature of +600.

The impeller carries 12 curved blades made of of stainless steel.

Corrosion-resistant models are made of stainless steel.

Explosion-proof - carbon steel and brass (for normal humidity), stainless steel and brass (for high humidity). Material for the most protected models: aluminum alloys.

The equipment is manufactured according to design diagrams No. 1 and No. 5. The power of the motors supplied in the kit ranges from 0.2 to 75 kW. Engines up to 7.5 with a rotation speed of up to 750 to 3000 rpm, more powerful ones - from 356 to 1000.

Service life - more than 6 years.

The model number reflects the diameter of the impeller: from No. 2.5 - 0.25 m. up to No. 20 - 2 m. (according to GOST 10616-90).

Parameters of some popular models:

1. VR 80-75 No. 2.5: engines (Dv) from 0.12 to 0.75 kW; 1500 and 3000 rpm; pressure (P) - from 0.1 to 0.8 kPa; productivity (Pr) - from 450 to 1700 m3/h. Vibration isolators (Vi) - rubber. (4 pcs) K.s. No. 1.

2. VR 80-75 No. 4: Dv from 0.18 to 7.5 kW; 1500 and 3000 rpm; P - from 0.1 to 2.8 kPa; Pr - from 1400 to 8800 m3/h. V - rubber. (4 pcs) K.s. No. 1.

3. VR 80-75 No. 6.3: Dv from 1.1 to 11 kW; 1000 and 1500 rpm; P - from 0.35 to 1.7 kPa; Pr - from 450 to 1700 m3/h. V - rubber. (4 pcs) K.s. No. 1.

4. VR 80-75 No. 10: Dv from 5.5 to 22 kW; 750 and 1000 rpm; P - from 0.38 to 1.8 kPa; Pr - from 14600 to 46800 m3-h. V - rubber. (5 pcs.) K.s. No. 1.

5. VR 80-75 No. 12.5: Dv from 11 to 33 kW; 536 and 685 rpm; P - from 0.25 to 1.4 ka; Pr - from 22000 to 63000 m3/h. V - rubber (6 pcs). K.s. No. 5.

6. Fan VTs 14 46 medium pressure.

The performance characteristics and materials for manufacturing are identical to the VR, with the exception of the number of blades (32 pcs).

Numbers - from 2 to 8. Construction diagrams No. 1 and No. 5.

Service life - more than 6 years. The guaranteed number of working hours is 8000.

Parameters and performance:

1. VTs 14 46 No. 2: Dv from 0.18 to 2.2 kW; 1330 and 2850 rpm; P - from 0.26 to 1.2 kPa; Pr - from 300 to 2500 m3/h. V - rubber. (4 pcs) K.s. No. 1.

2. VTs 14 46 No. 3.15: Dv from 0.55 to 2.2 kW; 1330 and 2850 rpm; P - from 0.37 to 0.8 kPa; Pr - from 1500 to 5100 m3/h. V - rubber. (4 pcs) K.s. No. 1.

3. VTs 14 46 No. 4: Dv from 1.5 to 7.5 kW; 930 and 1430 rpm; P - from 0.55 to 1.32 kPa; Pr - from 3500 to 8400 m3/h. V - rubber. (4 pcs) K.s. No. 1.

4. VTs 14-46 No. 6.3: Dv from 5.5 to 22 kW; 730 and 975 rpm; P - from 0.89 to 1.58 kPa; Pr - from 9200 to 28000 m3/h. V - rubber. (5 pcs) K.s. No. 1.5.

5. VTs 14-46 No. 8: Dv from 5.5 to 22 kW; 730 and 975 rpm; P - from 1.43 to 2.85 kPa; Pr - from 19,000 to 37,000 m3/h. V - rubber. (5 pcs) K.s. No. 1.5.

Dust fan "snail"

Dust fans are designed for harsh working conditions; their purpose is to remove air with fairly large particles (pebbles, dust, small metal shavings, wood shavings, wood chips) from the work site. The impeller carries 5 or 6 blades made of thick carbon steel. The units are designed to operate in machine exhaust hoods. Popular models are VCP 7-40. Performed according to K.s. No. 5.

They create pressure from 970 to 4000 Pa, they can be classified as “medium and high pressure”. The impeller numbers are 5, 6.3 and 8. Engine power is from 5.5 to 45 kW.

Others

There are devices of a special class - for blowing into solid fuel boilers. Produced in Poland. Specialized equipment for heating systems(private).

The “snail” body is cast from aluminum alloy. A special damper with a system of weights prevents air from entering the firebox when the motor is turned off. Can be installed in any position. Small motor with temperature sensor, 0.8 kW. Models WPA-117k, WPA-120k are on sale, differing in base sizes.

Comments:

After the air duct network has been designed and calculated, it is time to select the right one for this system. ventilation unit for air supply and treatment. With my heart ventilation system is the fan that drives air masses and designed to provide required consumption and network pressure. An axial type unit often plays this role. In order for the necessary parameters to be maintained, the axial fan must first be calculated.

An axial fan is used in duct systems to move large masses of air.

General concept of the design of the unit and its purpose

An axial fan is a bladed blower that transfers the mechanical energy of rotation of the impeller blades to the air flow in the form of potential and kinetic energy, and he spends this energy to overcome all resistance in the system. Impeller axis of this type is the axis of the electric motor, it is located in the center of the air flow, and the plane of rotation of the blades is perpendicular to it. The unit moves air along its axis due to blades turned at an angle to the plane of rotation. The impeller and electric motor are mounted on the same shaft and are constantly located inside the air flow. This design has its disadvantages:

1. The unit cannot move high-temperature air masses that could damage the electric motor. Recommended maximum temperature is 100°C.
2. For the same reason, it is not allowed to use this type of unit for moving aggressive media or gases. The transported air must not contain sticky particles or long fibres.
3. Due to its design axial fan cannot develop high pressure and is therefore unsuitable for use in ventilation systems of great complexity and length. Maximum pressure, which can provide modern unit axial type, is within 1000 Pa. However, there are special mine fans whose drive design allows pressure to be developed up to 2000 Pa, but then the maximum productivity is reduced to 18,000 m³/h.

The advantages of these machines are as follows:

• the fan can provide high air flow (up to 65,000 m³/h);
• the electric motor, being in the flow, is successfully cooled;
• the machine does not take up much space, is lightweight and can be installed directly in the channel, which reduces installation costs.

All fans are classified according to standard sizes, indicating the diameter of the machine's impeller. This classification can be seen in Table 1.

Table 1

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Description of calculations of blower machine parameters

The calculation of any type of ventilation unit is carried out according to individual aerodynamic characteristics, and an axial fan is no exception. These are the characteristics:

1. Volume flow or productivity.
2. Coefficient useful action.
3. The power required to drive the unit.
4. The actual pressure developed by the unit.

The performance was determined earlier when the ventilation system itself was calculated. The fan must provide it, so the air flow value remains unchanged for calculation. If the air temperature is work area differs from the temperature of the air passing through the fan, then the performance should be recalculated using the formula:

L = Ln x (273 + t) / (273 + tr), where:

• Ln — required productivity, m³/h;
• t is the temperature of the air passing through the fan, °C;
• tr is the air temperature in the working area of ​​the room, °C.

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Power determination

Once the required amount of air is finally determined, you need to find out the power required to create the design pressure at this flow rate. The power on the impeller shaft is calculated using the formula:

NB (kW) = (L x p) / 3600 x 102ɳв x ɳп, here:

• L - unit productivity in m³ per 1 second;
• p—required fan pressure, Pa;
• ɳв is the efficiency value, determined by the aerodynamic characteristic;
• ɳp is the efficiency value of the bearings of the unit, assumed to be 0.95-0.98.

The value of the installed power of the electric motor differs from the power on the shaft; the latter takes into account only the load in operating mode. When starting any electric motor, there is a jump in current strength, and therefore power. This starting peak must be taken into account in the calculation, so the installed power of the electric motor will be:

Ny = K NB, where K is the starting torque safety factor.

The values ​​of safety factors for various shaft powers are shown in Table 2.

table 2

If the unit is installed in a room in which the air temperature can reach +40° C for various reasons, then the Ny parameter should be increased by 10%, and at +50° C the installed power should be 25% higher than the calculated one. Finally, this parameter of the electric motor is taken from the manufacturer’s catalog, choosing the closest larger value to the calculated Ny with the calculation of all reserves. As a rule, the blower is installed before the heat exchanger, which heats the air for further supply to the premises. Then the electric motor will start and operate in cold air, which is more economical in terms of energy consumption.

Blower machines of different sizes can be equipped with electric motors of different power depending on the pressure required to be obtained. Each model of the unit has its own aerodynamic characteristics, which the manufacturing plant reflects in its catalog in graphical form. Efficiency is a variable value for various conditions work, it can finally be determined from the graphical characteristics of the fan, based on the values ​​of performance, flow and installed power calculated earlier.

The main task of calculating and selecting a fan is to meet the movement requirements required quantity air, taking into account the resistance of the air duct network, while achieving the maximum efficiency value of the unit.

The so-called snail for ventilation may not always mean the same type of forcing ventilation device- basic common features, this is the form of the unit, but by no means the principle of operation and direction of the air flow.

Injection devices of this type can:

• radically different in the design of the blades;
• and can also be of supply or exhaust type, that is, direct the flow in the opposite direction.

Ventilation snail

They are usually used for solid fuel boilers big size, production workshops and public buildings, but about all this below, and in addition - a video in this article.

Mechanical ventilation

Note. Blower/suction units with an electric motor, which are called “snails,” are not suitable for any type of ventilation, since they can only direct the air flow in one direction.

Types of ventilation

• As you can see in the top image, the word “ventilation” can mean completely different ways air exchange and some you may not have even heard of, but we will briefly consider only the most basic of them.
• Firstly, there is a well-known exhaust method, when warm or polluted air is removed from the room.
• Secondly, there is a supply option and most often this is the addition of fresh cool air.
• Thirdly, this is a combination, that is, a supply and exhaust option.
• The above systems can function naturally, but can also be forced using axial (axial), radial (centrifugal), diametrical (tangential) and diagonal fans. In addition, exhaust and air supply can be carried out either in general or in local mode. That is, the air duct is supplied to a specific destination and performs the function of blowing or exhaust.

Examples

Note. Below we will look at several types of snails that are used for.

BDRS 120-60 (Türkiye) is exhaust snail radial type with a weight of 2.1 kg, a frequency of 2325 rpm, a voltage of 220/230V/50Hz and a maximum power consumption of 90W. At the same time, BDRS 120-60 is able to pump a maximum of 380 m 3 /min of air with a temperature range from -15⁰C to +40⁰C, and has a safety class of IP54.

The BDRS brand can have several standard sizes; the external rotary motor is made of galvanized steel and is protected on the side by a chrome grille, which prevents foreign elements from getting onto the impeller.

The heat-resistant supply and exhaust radial fan Dundar CM 16.2H is usually used for pumping hot air from boilers operating on solid fuel, although the instructions allow it to also be used indoors for various purposes. The air flow during transportation can have a temperature from -30⁰C to +120⁰C, and the snail itself can be rotated to 0⁰ (horizontal position), 90⁰, 180⁰ and 270⁰ (motor on the right side).

The CM 16.2H model has a motor speed of 2750 rpm, a voltage of 220/230V/50Hz and a maximum power consumption of 460W. The unit weighs 7.9 kg and is capable of pumping a maximum volume of 1765 m 3 /min of air, a pressure level of 780 Pa, and has a protection degree of IP54.

Various modifications of VENTS VSCHUN can be used for the needs and air conditioning of premises for various purposes and have an air transportation capacity of up to 19000m 3 /hour.

Such a centrifugal scroll has a spiral-rotating body and an impeller, which is mounted on the axis of a three-phase asynchronous motor. The VSCHUN body is made of steel, which is later coated with polymers

Any modification implies the ability to rotate the body to the right or left. This allows you to connect to existing air ducts at any angle, but the step between the fixed position is 45⁰.

Also on different models Either two-stroke or four-stroke asynchronous motors with an external rotor can be used, and its impeller in the form of forward-curved blades is made of galvanized steel. Rolling bearings increase the operating life of the unit, factory-balanced turbines significantly reduce noise, and the protection level is IP54.

In addition, for VSCHUN it is possible to adjust the speed yourself using an autotransformer regulator, which is very convenient when:

• change of seasons;
• working conditions;
• premises and so on.

In addition, several units of this type can be connected to an autotransformer device at once, but at the same time mandatory the main condition must be met - their total power should not exceed the rating of the transformer.

Specifying a parameter	VTsUN
	140×74-0.25-2	140×74-0.37-2	160×74-0.55-2	160×74-0.75-2	180×74-0.56-4	180×74-1,1-2	200×93-0.55-4	200×93-1,1-2
Voltage (V) at 50Hz	400	400	400	400	400	400	400	400
Power consumption (kW)	0,25	0,37	0,55	0,75	0,55	1,1	0,55	1,1
Current)A)	0,8	0,9	1,6	1,8	1,6	2,6	1,6	2,6
Air flow maximum (m 3 /hour)	450	710	750	1540	1030	1950	1615	1900
Rotation speed (rpm)	1350	2730	1360	2820	1360	2800	1360	2800
Sound level at 3m (db)	60	65	62	68	64	70	67	73
Air temperature during transportation maximum t⁰C	60	60	60	60	60	60	60	60
Protection	IP54	IP54	IP54	IP54	IP54	IP54	IP54	IP54

a brief description of centrifugal fans

Centrifugal fans belong to the category of blowers with the greatest variety of design types. Fan wheels can have blades curved both forward and backward relative to the direction of rotation of the wheel. Fans with radial blades are quite common.

When designing, it should be taken into account that fans with backward blades are more economical and less noisy.

The fan efficiency increases with increasing speed and for conical wheels with backward blades can reach a value of 0.9.

Taking into account modern requirements To achieve energy saving when designing fan installations, one should focus on fan designs that correspond to the proven aerodynamic designs Ts4-76, 0.55-40 and similar to them.

Layout solutions determine the efficiency of the fan installation. With a monoblock design (wheel on an electric drive shaft), the efficiency has the maximum value. The use of a running gear in the design (a wheel on its own shaft in bearings) reduces the efficiency by approximately 2%. V-belt drive Compared to the clutch, it further reduces the efficiency by at least another 3%. Design decisions depend on fan pressure and speed.

According to the developed excess pressure General purpose air fans are divided into the following groups:

1. high pressure fans (up to 1 kPa);

2. medium pressure fans (13 kPa);

3. low pressure fans (312 kPa).

Some specialized high-pressure fans can reach pressures of up to 20 kPa.

Based on speed (specific speed), general-purpose fans are divided into the following categories:

1. high-speed fans (11 n s 30);

2. medium speed fans (30 n s 60);

3. high-speed fans (60 n s 80).

Design solutions depend on the flow required by the design task. For large flows, fans have double-suction wheels.

The proposed calculation belongs to the constructive category and is performed by the method of successive approximations.

Coefficients of local resistance of the flow part, coefficients of change in speed and ratios linear dimensions are set depending on the design pressure of the fan with subsequent verification. The criterion for the correct choice is that the calculated fan pressure corresponds to the specified value.

Aerodynamic calculation of a centrifugal fan

For calculation the following are specified:

1. Ratio of impeller diameters

2. The ratio of the diameters of the impeller at the gas outlet and inlet:

Lower values ​​are selected for high pressure fans.

3. Head loss coefficients:

a) at the entrance to the impeller:

b) on the impeller blades:

c) when turning the flow onto the working blades:

d) in a spiral outlet (casing):

Smaller values ​​of in, lop, pov, k correspond to low-pressure fans.

4. Speed ​​change coefficients are selected:

a) in a spiral outlet (casing)

b) at the entrance to the impeller

c) in working channels

5. The head loss coefficient is calculated, reduced to the flow velocity behind the impeller:

6. From the condition of minimum pressure loss in the fan, the coefficient Rв is determined:

7. The flow angle at the impeller inlet is found:

8. The speed ratio is calculated

9. The coefficient of theoretical pressure is determined from the condition of the maximum hydraulic efficiency of the fan:

10. The value of hydraulic efficiency is found. fan:

11. The angle of flow exit from the impeller is determined at the optimal value of G:

hail .

12. Required peripheral speed of the wheel at the gas outlet:

M/s .

where [kg/m3] is the air density under suction conditions.

13. Determined required number revolutions of the impeller in the presence of a smooth gas entry into the impeller

RPM .

Here 0 =0.91.0 is the coefficient of filling the section with the active flow. As a first approximation, it can be taken equal to 1.0.

The operating speed of the drive motor is taken from a number of frequency values ​​typical for electric fan drives: 2900; 1450; 960; 725.

14. Outside diameter impeller:

15. Impeller inlet diameter:

If the actual ratio of impeller diameters is close to that previously accepted, then no adjustments are made to the calculation. If the value is greater than 1m, then a fan with double-sided suction should be calculated. In this case, half the feed of 0.5 should be substituted into the formulas Q.

Elements of the velocity triangle when gas enters the rotor blades

16. The peripheral speed of the wheel at the gas inlet is found

M/s .

17. Gas speed at the entrance to the impeller:

M/s .

Speed WITH 0 should not exceed 50 m/s.

18. Gas speed in front of the impeller blades:

M/s .

19. Radial projection of the gas velocity at the entrance to the impeller blades:

M/s .

20. The projection of the input flow velocity onto the direction of the peripheral velocity is taken equal to zero to ensure maximum pressure:

WITH 1u = 0.

Because the WITH 1r= 0, then 1 = 90 0, that is, the gas inlet to the rotor blades is radial.

21. Relative speed of gas entry to the rotor blades:

Based on calculated values WITH 1 , U 1 , 1 , 1 , 1 a triangle of velocities is constructed as gas enters the rotor blades. With the correct calculation of speeds and angles, the triangle should close.

Elements of the velocity triangle when gas exits from the rotor blades

22. Radial projection of the flow velocity behind the impeller:

M/s .

23. Projection of the absolute gas exit velocity onto the direction of the peripheral velocity on the impeller rim:

24. Absolute gas speed behind the impeller:

M/s .

25. Relative speed of gas exit from the rotor blades:

Based on the obtained values WITH 2 , WITH 2u ,U 2 , 2 , 2 a velocity triangle is constructed as gas exits the impeller. With the correct calculation of speeds and angles, the speed triangle should also close.

26. Using the Euler equation, the pressure created by the fan is checked:

The calculated pressure must match the design value.

27. Width of the blades at the gas inlet to the impeller:

here: UT = 0.020.03 - coefficient of gas leakage through the gap between the wheel and the inlet pipe; u1 = 0.91.0 - filling factor of the input section of the working channels with the active flow.

28. Width of the blades at the gas outlet from the impeller:

where u2 = 0.91.0 is the active flow filling factor of the output section of the working channels.

Determination of installation angles and number of impeller blades

29. Angle of installation of the blade at the flow inlet into the wheel:

Where i- angle of attack, the optimal values ​​of which lie within -3+5 0.

30. Angle of installation of the blade at the gas outlet from the impeller:

where is the flow lag angle due to flow deflection in the oblique section of the interscapular channel. Optimal values ​​are usually taken from the interval at = 24 0 .

31. Average blade installation angle:

32. Number of working blades:

Round the number of blades to an even number.

33. The previously accepted flow lag angle is clarified according to the formula:

Where k= 1.52.0 with backward curved shoulder blades;

k= 3.0 with radial blades;

k= 3.04.0 with forward-curved blades;

The adjusted angle value should be close to the preset value. Otherwise, you should set a new value u.

Determination of fan shaft power

34. Total fan efficiency: 78.80

where mech = 0.90.98 - mechanical efficiency. fan;

0.02 - the amount of gas leaks;

d = 0.02 - coefficient of power loss due to friction of the impeller on the gas (disc friction).

35. Required power on the motor shaft:

25,35 kW.

Profiling of impeller blades

The most commonly used blades are those outlined in a circular arc.

36. Wheel blade radius:

37. We find the radius of centers using the formula:

R c =, m.

The blade profile can also be constructed in accordance with Fig. 3.

Rice. 3. Profiling fan impeller blades

Calculation and profiling of a spiral outlet

For a centrifugal fan, the outlet (volute) has a constant width B, significantly exceeding the width of the impeller.

38. The width of the cochlea is chosen constructively:

IN 2b 1 =526 mm.

The outline of the outlet most often corresponds to a logarithmic spiral. Its construction is carried out approximately according to the rule of the design square. In this case, the side of the square a four times less opening of the spiral casing A.

39. The value of A is determined from the relationship:

Where average speed gas leaving the cochlea WITH and is found from the relation:

WITH a =(0.60.75)* WITH 2u=33.88 m/s.

A = A/4 =79,5 mm.

41. Let's determine the radii of the arcs of circles forming a spiral. The starting circle for the formation of a cochlear spiral is the circle of radius:

Cochlea opening radii R 1 , R 2 , R 3 , R 4 is found using the formulas:

R 1 = R H +=679.5+79.5/2=719.25 mm;

R 2 = R 1 + A=798.75 mm;

R 3 = R 2 + a=878.25 mm;

R 4 = R 3 + A=957.75 mm.

The construction of the cochlea is carried out in accordance with Fig. 4.

Rice. 4.

Near the impeller, the outlet turns into a so-called tongue, which separates the flows and reduces leakage inside the outlet. The part of the outlet limited by the tongue is called the outlet part of the fan housing. Outlet length C determines the area of ​​the fan outlet. The outlet part of the fan is a continuation of the exhaust and performs the functions of a curved diffuser and a pressure pipe.

The position of the wheel in the spiral outlet is set based on the minimum hydraulic losses. To reduce losses from disk friction, the wheel is shifted to the rear wall of the outlet. The gap between the main wheel disk and the rear outlet wall (drive side) on the one hand, and the wheel and tongue on the other, is determined by the aerodynamic design of the fan. So, for example, for the Ts4-70 scheme they are 4 and 6.25%, respectively.

Profiling the suction pipe

The optimal shape of the suction pipe corresponds to the tapering sections along the gas flow. Narrowing the flow increases its uniformity and promotes acceleration when entering the impeller blades, which reduces losses from the impact of the flow on the edges of the blades. Best performance has a smooth confuser. The interface of the confuser with the wheel should ensure a minimum of gas leaks from the discharge to the suction. The amount of leakage is determined by the gap between the outlet part of the confuser and the entrance to the wheel. From this point of view, the gap should be minimal; its real value should depend only on the magnitude of the possible radial runout of the rotor. Thus, for the aerodynamic design of the Ts4-70, the gap size is 1% of the outer diameter of the wheel.

The smooth confuser has the best performance. However, in most cases, a regular straight confuser is sufficient. The inlet diameter of the confuser must be 1.32.0 times greater than the diameter of the suction hole of the wheel.

Depending on the size and performance of such units, the operating conditions will also depend: in addition to domestic use, many types of ventilation equipment are widely used in the industrial sector. One example of such equipment is a rounded snail hood.

A radial centrifugal fan of this type is most often installed in production premises and is used to clean the air from dust, sawdust, burning, sand and other industrial waste. A similar air treatment system can be installed in multi-storey building, for example, in a ventilation shaft.

Let's understand the principle of its operation and consider the main stages of constructing a snail hood with your own hands.

Design Features

Scroll hoods differ in structure from standard fans with large blades. Air flows in such equipment move due to centrifugal force resulting from the rotation of a wheel with small specially shaped blades. The speed and power of such hoods may vary depending on the number of blades and motor parameters.

The air purification scheme in radial centrifugal hoods is quite simple: when air gets inside the hood, it begins to be sucked into the rotor, where it begins to rotate and is subject to pressure, gradually moving towards the outlet and being cleared of foreign elements. The general shape of the inlet and outlet channels resembles a snail - hence the name of this hood.

Attention! Designs of this type are useful in that they can both suck in air and ensure its outflow.

The housing of this type of ventilation system is made of durable materials, such as aluminum, brass or steel. Also available for sale plastic structures, but they are less durable and rarely operate at peak efficiency.

Since air treatment can be carried out at high temperatures, the body is processed protective paint, substances resistant to chemicals, and also coated with polymers.

Rotational mechanisms in such a system can be single, or may include two disks with blades required sizes. Both radial and circular blade placement provide high performance device.

Advice: For better cleaning air, purchase fans in which the blades are slightly curved rather than flat.

Despite the uniform shape, such hoods are suitable for many operating conditions, since they differ in orientation to the right or left side, and in overall dimensions. Average the diameter of the main body of such a hood can be from 25 to 150 cm.

For ease of installation for industrial purposes, many structures of this type are created modular, and fastening bolts are used to connect them. Accordingly, you can change both the angle of inclination and the details of some parts of such a design for greater efficiency: It’s better to first calculate all the parameters with specialists.

Since snails can differ from each other, you should not focus solely on size and power ratings. Familiarize yourself with their varieties - and make a choice, relying on future operating conditions.

Types of equipment

First of all, snail hoods differ in pressure indicators. Ventilation can be carried out under the following conditions:

• low pressure – up to 100 kg/m2;
• medium – from 100 dl 300 kg/m2;
• high pressure - more than 300 kg/m2 (can reach 1200 kg/m2).

The first type of hoods is suitable for use in both industrial and living conditions. As a rule, such equipment is quite compact, so it can be installed without additional help.

Attention! Low-pressure hoods are sufficient to ensure high-quality air ventilation in the shafts of multi-storey buildings.

Medium pressure fans are used for industrial purposes. Such equipment can more easily withstand difficult conditions operation, it is equipped in accordance with the main fire and technical requirements in production.

The third option is used not only in workshops, but also in laboratories, warehouses, areas where painting is carried out, etc. They can be installed for blowing air conditioning systems or working machines, as well as for pumping air in boiler systems.

Depending on the quality and degree of wear of the structure, there are general volute hoods, heat-resistant, corrosion-resistant systems, as well as heavy-duty equipment that can withstand even explosive reactions.

In most cases, snail-shaped air ventilation systems are used to remove pebbles, wood and metal shavings, wood chips and other production residues from the premises. Their installation must be carried out taking into account safety and labor protection requirements.

How to make it yourself

One of the features of such snails is their different price range. The minimum price for a snail hood will be about 3 thousand, but such devices, as a rule, are not very powerful and are very limited in size. The average price of a high-quality unit will exceed 20 thousand rubles.

Therefore, for domestic needs it is more expedient to produce homemade snail for hood. Standard design such a body will consist of two parts: the engine will be located in one zone, and the blowing blades in the other.

The casing for the snail can be purchased at hardware stores. If you are going to make it yourself, purchase the motor and other parts in advance, since the dimensions will have to be adjusted. It is better to make the case from metals (for example, aluminum and steel). Plastic will be less resistant to mechanical damage, and the tree will quickly catch fire in case of malfunctions.

The fan in such a system will operate at high speed. Therefore, incorrect design of the hood can have bad consequences. Check the quality and reliability of not only the base itself and fastening mechanisms, but also the motor, impeller and fan.

The fan dimensions are selected taking into account the area and degree of contamination of the room. Industrial designs are large.

Important! When installing the motor inside the box of such a hood, make sure that the design includes cooling holes. High temperature stress on the system can lead to an explosion.

Pay special attention to the choice internal materials. Fan operation can be affected not only by temperature, but also by the power of air flow, the amount of debris and dust.

When air with large impurities is sucked in, the blades of the rotating wheel may be damaged. And in order to thoroughly clean the air, the unit must operate at high speed and under high pressure- this creates additional stress on the entire internal structure. That's why it is better to choose parts made of durable materials, such as steel or aluminum.

• choose the right engine size and power: take into account the maximum load on the structure, as well as the required operating speed of the hood;
• When installing such a system vertically, carefully check that the fan and wheel are securely fastened: with rapid air currents they can jump off or change their location;
• materials adjacent to such a hood must be fireproof, like all the parts used in its assembly;
• maintain proportions between individual hood zones: in standard models offered in stores, the optimal ratio of length and width of the structure is taken into account;
• If you are not sure that the assembled hood is safe, contact specialists who will check its serviceability.

note that snail hoods are rarely used in living rooms . Firstly, they take up a lot of space, and secondly, in rooms like a kitchen, the flow of polluted air can have different directions, so it is best to install such a hood in a ventilation shaft, where all the air coming from the apartment is concentrated.

The design of such structures will also play an important role in living rooms, but it is not diverse and does not always harmonize with the interior.

Advice: when placing such a hood in open conditions(outside) make sure weather will not affect its functionality.

Ventilation hoods can be used not only for air purification. In domestic conditions they are excellent cope with heating the room, and also affect the humidity in the room.

The cost of equipment intended for domestic and industrial needs will differ significantly, but, in any case, such units have sufficient power for full operation.

For an example of designing a snail hood, see the attached video.

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