Fan radial snail make shroud drawing. What is a ventilation cochlea: device features. Appropriateness for home use

Snail fans get their name from the shape of the body, which resembles the shell of this mollusk. Today, this type of equipment is used both in industry and in housing construction in ventilation systems. Manufacturers today offer several models of snails for ventilation. But they all work on the same principle - the centrifugal force created by the rotation of the blades on the rotor captures air through the volute-shaped inlet and pushes it through a rectilinear outlet located at 90 ° in another plane to the inlet.

General information about centrifugal (radial) fans

Scroll fans have a dual designation (marking): VR and VC, that is, radial and centrifugal. The first suggests that the blades of the working body of the equipment are located radially relative to their rotor. The second is the notation physical principle the operation of the device, that is, the process of intake and movement of air masses occurs due to centrifugal force.

Exactly centrifugal fans in ventilation systems have shown themselves with positive side at the expense high efficiency air outlet.

Operating principle

As already mentioned, the fans of this modification operate on the basis of centrifugal force.

The blades mounted on the rotor of the device rotate at high speed, creating turbulence inside the housing.
The inlet pressure drops, which causes nearby air to be sucked in and rush in.
Under the action of the blades, it is thrown to the periphery of the space, where high pressure is created.
Under its action, the air flow rushes to the outlet pipe.

This is how all centrifugal models work, which are installed not only in ventilation systems, but also in smoke removal systems. About the latter, it must be said that their body is made of aluminum alloy or steel coated with heat-resistant materials, and are equipped with an explosion-proof electric motor.

Design features

As already mentioned, the main feature of the design is the snail. It is necessary to indicate the shape of the blades. Three types of fans are used in fans of this brand:

straight slope,
tilted back
in the form of a wing.

The first position is small fans with great power and performance. That is, they can create conditions under which other models require large body. At the same time, they work with low level noise. The second position is economical option, which consumes 20% less electricity than other positions. Such fans easily carry loads.

As for the execution, which refers to the electric motor, there are also three positions:

the rotor is fixed directly to the motor shaft through the coupling and bearings;
through a belt drive using pulleys;
the impeller is mounted on the motor shaft.

And one more feature is the connection points of the fan with air ducts ventilation system. The inlet has rectangular shape holes, outlet round.

Kinds

Types of centrifugal snail fans are three positions that differ from each other in power. This parameter depends on the speed of rotation of the electric motor, and, accordingly, the rotor, as well as on the number of blades in the design of the device. Here are three types:

Low pressure scroll fans, the parameter of which does not exceed 100 kg/cm². Most often they are used in ventilation systems. apartment buildings. Install snails on roofs.
Medium pressure models - 100-300 kg / cm². Are established in systems of ventilation of industrial objects.
Variety high pressure– 300-1200 kg/cm². These are powerful fan units, which are usually included in the air exhaust system of paint shops, in industries where pneumatic transport is installed, in warehouses with fuels and lubricants and other premises.

There is another division of snail fans - according to their purpose. These are first and foremost appliances. general purpose. Then there are three more positions: explosion-proof, heat-resistant and corrosion-resistant.

Usage restrictions

with sticky suspensions with a concentration of more than 10 mg/m³;
with fibrous materials in the air;
with explosive inclusions;
with corrosive particles;
and warehouses where explosives are stored.

In all other cases, snails can be used without restrictions. And one more point regulating the conditions of their operation is temperature regime, which must not be violated: from -45C to + 45C.

Popular Models

In principle, there is no model division of snails. There are certain brands that are produced by all manufacturers. And they are divided mainly for their intended purpose. For example, a VRP fan, where the letter “P” means that this is a dust model that is used in ventilation and aspiration systems to remove air with a high concentration of dust. That is, this is a specific model that should be used exactly for its intended purpose. Of course, this device can easily cope with ordinary air, but it is more expensive than standard VR or VC, because its design uses thick metal for the manufacture of the body and blades, hence the higher power of the electric motor.

The same applies to fans of the brand VR DU, that is, for smoke extraction. They are made from more quality materials with installation of an explosion-proof motor. Hence their high price. As for other positions, BP is divided into types that have already been mentioned, and each group has its own models with their own technical characteristics.

How to DIY

The question posed by the title of this section can be classified as rhetorical. That is, in principle, you can make a snail with your own hands if you have the skills of a tinsmith or welder. Because the device will have to be assembled from sheet metal. And depending on the power and performance of the device, the metal will be of different thicknesses.

Plus, it’s difficult to make blades on your own and attach them to the rotor with high quality. Because the rotor will rotate at a tremendous speed, and if the balance of the structure is disturbed, the fan will blow apart in the first 20 seconds of operation. Yes, and it is necessary to choose the right electric motor, taking into account the power and speed of rotation, plus correctly connect it to the fan rotor. So do not try to do anything with your own hands - it is dangerous for your own life.

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 bent 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 efficiency of the fan increases with increasing speed and for conical wheels with backward blades can reach 0.9.

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

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

According to the developed overpressure 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 develop pressures up to 20 kPa.

According to the 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 s60);

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

Structural solutions depend on the supply required by the design task. At high flows, the fans have double suction wheels.

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

The coefficients of local resistance of the flow path, the coefficients of change in speed and the ratio of linear dimensions are set depending on the design pressure of the fan with subsequent verification. The criterion for the correct choice is the compliance of the calculated pressure of the fan with the set value.

Aerodynamic calculation of a centrifugal fan

For the calculation are given:

1. Ratio of impeller diameters

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

Smaller values are selected for high pressure fans.

3. Pressure loss coefficients:

a) at the impeller inlet:

b) on the impeller blades:

c) when turning the flow on the rotor blades:

d) in a spiral outlet (casing):

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

4. The coefficients of change in speed 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 Rv is determined:

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

8. The ratio of speeds 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 the hydraulic efficiency is found. fan:

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

hail .

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

m/s .

where [kg / m 3 ] - air density under suction conditions.

13. The required number of revolutions of the impeller is determined in the presence of a smooth entry of gas into the impeller

RPM .

Here 0 =0.91.0 is the filling factor of the section with 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 fan electric drives: 2900; 1450; 960; 725.

14. Outer diameter of impeller:

15. Impeller inlet diameter:

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

Elements of the velocity triangle at the gas inlet to the rotor blades

16. Is the circumferential speed of the wheel at the gas inlet

m/s .

17. Gas velocity at the impeller inlet:

m/s .

Speed FROM 0 must not exceed 50 m/s.

18. Gas velocity 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 rate on the direction of peripheral speed is taken zero for maximum pressure:

FROM 1u = 0.

Because the FROM 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:

According to the calculated values FROM 1 , U 1 , 1 , 1 , 1 a velocity triangle is constructed at the gas inlet to the rotor blades. With the correct calculation of velocities and angles, the triangle should close.

Elements of the triangle of speeds at the exit of gas from the working blades

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

m/s .

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

24. Absolute gas velocity behind the impeller:

m/s .

25. Relative speed of gas outlet from rotor blades:

According to the received values FROM 2 , FROM 2u ,U 2 , 2 , 2 a triangle of speeds is built when the gas leaves the impeller. With the correct calculation of velocities and angles, the triangle of velocities should also close.

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

The design pressure must match the design value.

27. The 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 inlet section of the working channels with active flow.

28. The width of the blades at the gas outlet from the impeller:

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

Determination of installation angles and number of impeller blades

29. Blade installation angle at the flow inlet to the impeller:

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

30. Blade installation angle at the gas outlet from the impeller:

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

31. Average installation angle of the blade:

32. Number of rotor blades:

Round the number of blades to an even integer.

33. The previously accepted flow lag angle is specified by the formula:

where k= 1.52.0 with backward curved blades;

k= 3.0 with radial blades;

k= 3.04.0 with forward-curved blades;

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

Determining the power on the fan shaft

34. Total fan efficiency: 78.80

where fur \u003d 0.90.98 - mechanical efficiency. fan;

0.02 - value of gas leaks;

q = 0.02 - coefficient of power loss due to friction of the impeller against gas (disk friction).

35. Required power on the motor shaft:

25,35 kW.

Profiling of impeller blades

The most commonly used blades are outlined along an arc of a circle.

36. Radius of wheel blades:

37. The radius of the centers is found by the formula:

R c =, m.

The construction of the blade profile can also be performed in accordance with Fig. 3.

Rice. 3. Profiling of fan impeller blades

Spiral Calculation and Profiling

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

38. The width of the snail is chosen constructively:

AT 2b 1 =526 mm.

The outlines of the tap most often correspond to a logarithmic spiral. Its construction is carried out approximately according to the constructor square rule. In this case, the side of the square a four times less than the opening of the spiral case A.

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

where is the average velocity of the gas at the outlet of the snail FROM and is found from the relation:

FROM a \u003d (0.60.75) * FROM 2u=33.88 m/s.

a = BUT/4 =79,5 mm.

41. Determine the radii of the arcs of circles forming a spiral. The initial circle for the formation of the spiral of the cochlea is the circle of radius:

Snail opening radii R 1 , R 2 , R 3 , R 4 we find by 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 snail is carried out in accordance with fig. four.

Rice. four.

Near the impeller, the branch turns into a so-called tongue, which separates the flows and reduces overflows inside the branch. 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 outlet and performs the functions of a curved diffuser and 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 disk of the wheel and the rear wall of the outlet (on the 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.

Suction pipe profiling

The optimal shape of the suction pipe corresponds to the narrowing sections along the gas flow. The narrowing of the flow increases its uniformity and contributes to the acceleration at the entrance to 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 coupling of the confuser with the wheel should ensure a minimum of gas leakage from the discharge to the suction. The amount of leakage is determined by the gap between the outlet part of the confuser and the wheel inlet. From this point of view, the gap should be minimal, its real value should depend only on the magnitude of the possible radial beats of the rotor. So, for the aerodynamic scheme Ts4-70, the gap size is 1% of the outer diameter of the wheel.

The best performance has a smooth confuser. However, in most cases, the usual direct confuser is sufficient. The inlet diameter of the confuser must be 1.3-2.0 times greater than the diameter of the wheel suction hole.

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

38. The width of the snail is chosen constructively:

AT»2 b 1 =526 mm.

39. Size BUT determined from the ratio:

where is the average velocity of the gas at the outlet of the snail FROM and is found from the relation:

FROM a \u003d (0.6¸0.75) * FROM 2u=33.88 m/s.

a = BUT/4 =79,5 mm.

41. Determine the radii of the arcs of circles forming a spiral. The initial circle for the formation of the spiral of the cochlea is the circle of radius:

, mm.

Snail opening radii R 1 , R 2 , R 3 , R 4 we find by the formulas:

R 1 = R H + \u003d 679.5 + 79.5 / 2 \u003d 719.25 mm;

R 2 = R 1 + a=798.75 mm;

R 3 \u003d R 2 + a=878.25 mm;

R 4 = R 3 + a=957.75 mm.

The construction of the snail is carried out in accordance with fig. four.

Rice. 4. Profiling the fan volute using the design square method

Comments:

After the air duct network is designed and calculated, it is time to choose a ventilation unit for this system for supplying and processing air. The heart of the ventilation system is a fan that drives the air masses and is designed to provide the necessary flow and pressure in the network. In this capacity, an axial-type unit often acts. In order for the necessary parameters to be maintained, it is first necessary to calculate axial fan.

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 blade blower that transmits mechanical energy rotation of the blades of the impeller to the air flow in the form of potential and kinetic energy, and it expends this energy to overcome all resistances in the system. The axis of the impeller 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 the blades turned at an angle to the plane of rotation. The impeller and motor are mounted on the same shaft and are constantly inside the air stream. This design has its drawbacks:

The unit cannot move air masses with high temperature which could damage the motor. Recommended Maximum temperature— 100°C.
For the same reason, it is not allowed to use this type of units to move aggressive media or gases. The transported air must not contain sticky particles or long fibres.
Due to its design, an axial fan cannot develop high pressure, therefore it is unsuitable for use in ventilation systems of great complexity and length. The maximum pressure that can provide modern unit axial type, is within 1000 Pa. However, there are special mine fans, the drive design of which allows to develop pressure up to 2000 Pa, but then the maximum performance decreases - up to 18000 m³ / h.

The advantages of these machines are as follows:

the fan can provide a large air flow (up to 65000 m³/h);
the electric motor, being in the stream, is successfully cooled;
the machine does not take up much space, is light in weight 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 impeller. This classification can be seen in Table 1.

Table 1

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Description of Blower Parameter Calculations

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

Volume flow or productivity.
Efficiency.
The power required to drive the unit.
The actual pressure developed by the unit.

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

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

Ln is the required capacity, 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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Determination of power

Once the required amount of air has been finally determined, it is necessary to find out the power required to create the design pressure at this flow rate. Calculation of power on the shaft of the impeller is carried out according to the formula:

NB (kW) = (L x p) / 3600 x 102ɳv x ɳp, here:

L is the capacity of the unit in m³ for 1 second;
p is the required fan pressure, Pa;
ɳv is the value of efficiency, determined by the aerodynamic characteristic;
ɳp - the value of the efficiency of the bearings of the unit, taken 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 the operating mode. When starting any electric motor, there is a jump in current, 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 the safety factors for different shaft power are shown in Table 2.

table 2

If the unit is installed in a room where the air temperature can reach up to different reasons+40° C, then the parameter Ny 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 according to the catalog of the manufacturing plant, choosing the nearest greater value to the estimated Ny with the calculation of all stocks. As a rule, the blower is installed before the heat exchanger, which heats the air for its further supply to the premises. Then the electric motor will start and run in cold air, which is more economical in terms of power consumption.

Blowers of different sizes can be equipped with electric motors of different power, depending on the pressure that you want to get. Each model of the unit has its own aerodynamic characteristic, which the manufacturer reflects in his catalog in graphical form. Efficiency is a variable value for various conditions work, it will finally be possible to find out by the graphic characteristic of the fan, based on the values of productivity, flow rate and installed power calculated earlier.

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

Ventilation of industrial premises is a necessity that allows you to maintain the health of workers and ensure the smooth operation of the workshop. To clean the air from various impurities, metal and wood chips, dust and dirt, powerful ventilation units « snails ". The design of these units includes several fans of different power, and therefore the "snail" can cope with almost any pollution.

Principle of operation

The name of the hood "snail" comes from design features and appearance ventilation. In its shape, it really resembles a twisted snail shell. The principle of operation of such a system is extremely simple. It is based on the centrifugal force that the turbine wheel sets. As a result, contaminated air masses enter the suction pipe, which, after passing through the cleaning system, return to the room or are discharged outside.

Types of snails

Hoods - snails may vary in terms of operating pressure. Each species has its own recommendations for use, namely:

Low pressure fans — up to 100 kg/m2. These designs can be used both in household and in industrial premises. They are compact and do not require additional labor during installation.
Medium pressure fans – up to 300 kg/m2. For such systems, industrial use is relevant. They do a great job with various impurities.
High pressure fans – up to 1200 kg/m2. Such fans are installed in hazardous industries, laboratories and paint shops.

Depending on the specifics of production, fire-resistant, corrosion-resistant or even explosion-resistant models can be purchased. The price of such products can be much higher, but safety at work should be in the first place.

Also, "snails" can be divided into inlet and outlet. Combining two snails different type into one system, you can easily create a supply and exhaust system that will not only remove polluted air masses, but also supply clean air to the room. Moreover, this exhaust system It can also be used as space heating during the cold season.

Operating restrictions

Despite the strength and reliability of industrial "snails", there are some restrictions on their use. So, centrifugal fans, which are called “snails” in everyday life, are not recommended to be installed if:

In the air there are sticky suspensions of more than 10 mg/m3.
There are explosive particles in the room.
The room temperature is outside the range of -40 to +45°C.

Moreover, it is rational to use “snail” ventilation in large rooms; in everyday life, it is better to install such devices in ventilation shafts, where all the exhaust air from the house enters.

Appropriateness for home use

Most often, a “snail” for ventilation is still used in industrial premises or in home carpentry shops, paint booths, etc. It is not advisable to install such ventilation directly in residential premises. After all, a “snail” is a plain-looking and fairly large device that can ruin overall design kitchens. In addition, this type of ventilation is quite noisy and can create significant discomfort during home use.

DIY snail

For domestic use you can make ventilation with your own hands. Of course, such a design will differ from an industrial installation, but it will help to significantly save money on the purchase of ventilation. It is worth noting that a high-quality medium-power snail in specialized stores costs around 20 thousand rubles, and therefore for many it remains topical issue, how to make ventilation with your own hands .
The design of the body of a homemade snail most often includes two parts - an area for placing the engine and an area with blowing blades. Most spare parts will have to be purchased in specialized stores, but these costs will be much lower than if you buy ready ventilation. So, you will need:

Frame. It can be bought at hardware store. It is better to give preference to a metal product.
Engine. Sold in the markets and electrical stores.
Working wheel. Can be purchased from electrical supply stores.
Fan. Sold in any store of household ventilation equipment.

Creating a ventilation unit with your own hands begins with calculations. In order for the use of snail ventilation to be effective, it is necessary to correctly calculate the power and size of the engine. When installing the device Special attention it is necessary to pay attention to the reliability of the fastenings of the fan and the impeller. At strong currents air, these components can become loose and come off, which will invariably lead to damage to ventilation. All parts, including the body, must be made of refractory materials.

Scheme of the ventilation "snail"

It should be noted that self assembly such an extraction can only be carried out with certain knowledge. If you are not sure that a device assembled by yourself is completely safe, it is better to consult a professional who can assess the correctness of your assembly. If assembly skills electrical structures you do not have, it is better to buy a ready-made device.