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

The units are called centrifugal (and also radial) because of the way the air flow is created by rotating a radial blade-type impeller (drum or cylinder shape) inside a spiral chamber. The blade profile can be straight, curved, "wing profile". Depending on the speed of rotation, the 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 pumps clean air into the room. You can change the rotation using a toggle switch that changes the phases of the current in places at the terminals of the electric motor.

The body of general-purpose equipment for operation 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 evaporations 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 working in hazardous conditions (mining equipment, a high content of explosive dust), more ductile metals (copper) and aluminum alloys are used. Equipment for explosive environments is characterized by increased massiveness and during operation eliminates sparking (the main cause of dust and gas explosions).

Drum ( Working wheel) with blades is made of steel grades that are not subject to corrosion and are ductile enough to withstand long-term 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 emit less noise. But the pressure of the air flow is still lower than that of a drum on which blades with an aerodynamic “wing profile” are installed.

"Snail" refers to equipment with increased vibration, the reasons for which are precisely in the low level of balance of the rotating impeller. Vibration has two effects: elevated level noise and destruction of the base on which the unit is installed. Damping springs that are inserted between the base of the housing and the installation site help to reduce the level of vibration. When mounting 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 color for operation in aggressive gas environments. Mainly asynchronous motors with a certain speed. Electric motors are designed to operate from a single-phase network (220 V) or three-phase (380 V). (The power of single-phase electric motors does not exceed 5 - 6 kW). In exceptional cases, a speed-controlled motor with thyristor control can be installed.

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

Direct connection. The shafts are connected with a keyed bushing. "Constructive scheme No. 1".
through the gearbox. The gearbox can have several gears. "Constructive scheme No. 3".
Belt-pulley transmission. The speed of rotation can change if you change the pulleys. "Constructive scheme No. 5".

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

The casing is made in 8 positions of the outlet relative to the vertical, from 0 to 315 through 45 degrees. This makes it easier to attach the unit to the 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 with durable powder paints with increased impact resistance.

Popular VR and VC models

1. Fan VR 80 75 low pressure

Created for ventilation systems production and public buildings. Working conditions: temperate and subtropical climate, in non-aggressive conditions. The temperature range suitable for the operation of general purpose equipment (OH) is from -40 to +40. Heat-resistant models withstand an increase of up to +200. Material: carbon steel. Average humidity level: 30-40%. Smoke extractors can work for 1.5 hours at a temperature of +600.

The impeller carries 12 curved stainless steel blades.

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 schemes No. 1 and No. 5. The power of the motors supplied in the kit is from 0.2 to 75 kW. Engines up to 7.5 with a speed of up to 750 to 3000 rpm, more powerful - 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 running 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. BP 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. Vee - rubber. (4 pcs) K.s. No. 1.

3. BP 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. Vee - rubber. (4 pcs) K.s. No. 1.

4. BP 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. Vee - rubber. (5 pcs.) K.s. No. 1.

5. BP 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. Wee - rubber (6 pcs). K.s. No. 5.

6. Fan VTS 14 46 medium pressure.

Performance characteristics and materials for manufacturing are identical to BP except for the number of blades (32 pcs).

Numbers - from 2 to 8. Structural schemes 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. Vee - 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. Vee - 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. Vee - 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. Vee - 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 19000 to 37000 m3 / h. Vee - 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 from the place of work with fairly large particles (pebbles, dust, small metal chips, wood chips, wood chips). The impeller carries 5 or 6 blades made of thick carbon steel. The units are designed to work in extracts from machine tools. VCP 7-40 models are popular. Performed according to K.s. No. 5.

They create pressure from 970 to 4000 Pa, they can be classified as "medium and high pressure". Impeller numbers - 5, 6.3 and 8. Engine power - from 5.5 to 45 kW.

Other

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

The case — "snail" is cast from an aluminum alloy. A special damper with a system of weights prevents air from entering the firebox when the engine is off. Can be installed in any position. Small motor with temperature sensor, 0.8 kW. On sale models WPA-117k, WPA-120k, differing in the size of the base.

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 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 for 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 solutions determine the efficiency of the 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%. The V-belt transmission, compared with 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.

Coefficients of local resistance of the flow path, coefficients of speed change and ratios 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 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 the circumferential velocity is taken equal to zero to ensure 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 back wall outlet (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.

Ministry of Education and Science of the Russian Federation

FGAOU HPE "Ural Federal University named after the first President of Russia B.N. Yeltsin"

Department of Industrial Heat Power Engineering

COURSE PROJECT

discipline: "Heat engines and superchargers"

on the topic: "Calculation of a console-type centrifugal blower fan"

Student Yakov D.V.

Group EN-390901

Teacher Kolpakov A.S.

Yekaterinburg 2011

1. Initial data

Calculation results

Brief description of centrifugal fans

Aerodynamic calculation of a centrifugal fan

Mechanical calculation

Fan drive selection

Bibliography

1. Initial data

Table 1.

	Name		Unit meas.
	Fan performance		thousand m3/hour
	Total fan pressure
	Gas parameters at the inlet to the unit:
	Absolute pressure
	Temperature
	Density
	Molecular weight of gas
	Accepted source system coefficients:

	Pressure loss coefficients:
	At the entrance to the impeller
	On the impeller blades
	When turning the flow on the rotor blades

	speed change factors:
	In a spiral outlet (casing)
	At the entrance to the impeller

The working fluid in all proposed options for calculating a centrifugal fan is air.

2. Calculation results

Table 2.

Name		Unit meas.
Fan type	console type
Hydraulic efficiency
Mechanical efficiency
General efficiency
Shaft power
Speed
The geometry of the flow path of the unit:
Inlet wheel clearance
Blade inlet diameter
Ratio of lumen and inlet diameters
Shaft diameter
Wheel diameter
Outlet to inlet diameter ratio (wheel modulus)
Inlet wheel width
Outlet wheel width
Blade angle at inlet
Outlet blade angle
Number of wheel blades
Elements of the velocity triangle at the impeller inlet:
Impeller entry speed
The rate of gas entry to the blades
Peripheral speed

The angle of the flow entry to the impeller blades
Elements of the triangle of speeds at the outlet of the impeller:
Impeller exit speed
Peripheral speed
Relative flow rate
Flow swirl
Speed ratio C2r/U2
Wheel exit angle
Profiling the impeller blades with an arc of a circle
Center circle radius
Blade profile circle radius

. Brief description of centrifugal fans

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 it can reach a value of ~0.9.

According to the developed overpressure, general purpose air fans are divided into the following groups:

High pressure fans (up to 1 kPa);

Medium pressure fans (1¸3 kPa);

Low pressure fans (3¸12 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:

High Speed Fans (11<n s<30);

Medium speed fans (30<n s<60);

Fast 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.

4. Aerodynamic calculation of a centrifugal fan

For the calculation are given:

Impeller diameter ratio

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

Smaller values are selected for high pressure fans.

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 x in, x lop, x pov, x to match low pressure fans.

The speed change coefficients are selected:

a) in a spiral outlet (casing)

b) at the entrance to the impeller

;

c) in working channels

From the condition of minimum pressure loss in the fan, the coefficient is determined R in:

The flow angle at the impeller inlet is:

, deg.

The ratio of speeds is calculated

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

The value of the hydraulic efficiency is found. fan:

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

, deg .

Required circumferential speed of the wheel at the gas outlet:

, m/s .

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

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

, rpm .

Here m 0 =0.9¸1.0 - section filling factor 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.

Impeller outer diameter:

, mm .

Impeller inlet diameter:

, mm .

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 .

Gas velocity at the impeller inlet:

, m/s .

Speed FROM 0 must not exceed 50 m/s.

Gas velocity in front of the impeller blades:

, m/s .

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

m/s .

The projection of the input flow velocity on the direction of peripheral velocity is taken equal to zero to ensure maximum head:

FROM 1u = 0.

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

Relative speed of gas entry to the rotor blades:

w 1 =, m/s.

According to the calculated values FROM 1 , U 1 , w 1 , a 1 , b 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 .

The projection of the absolute velocity of the gas outlet on the direction of peripheral velocity on the rim of the impeller:

Absolute gas velocity behind the impeller:

, m/s .

Relative speed of gas outlet from rotor blades:

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

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

Pa .

The design pressure must match the design value.

Blade width at the gas inlet to the impeller:

, mm,

here: a UT = 0.02¸0.03 - coefficient of gas leakage through the gap between the wheel and the inlet pipe; m u1 = 0.9¸1.0 - filling factor of the inlet section of the working channels with active flow.

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

, mm,

where mu2= 0.9¸1.0 - 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:

, hail,

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

Blade angle at the gas outlet from the impeller:

, hail,

Average installation angle of the blade:

, deg.

Number of rotor blades:

Round the number of blades to an even integer.

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

where k= 1.5¸2.0 with backward curved blades;

k= 3.0 with radial blades;

k= 3.0¸4.0 with forward curved blades;

b 2l = ;

s =b 2l - b 2 =2

Corrected angle value s should be close to the preset value. Otherwise, you should set a new value σ .

Determining the power on the fan shaft

34. Total fan efficiency: 78.80

where h fur = 0.9¸0.98 - mechanical efficiency fan;

0.02 - value of gas leaks;

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

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.

Radius of wheel blades:

, m.

The radius of the centers is found by the formula:

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.

The width of the snail is chosen constructively:

AT»2 b 1 =526 mm.

39. Size BUT determined from the ratio:

, m.

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.

Let us determine the radii of the arcs of the circles forming the 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:

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

R 2 = R 1 + a=798.75 mm;

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

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. The 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.

. Mechanical calculation

fan blade wheel drive

1. Verification calculation of impeller blades for strength

During fan operation, the blades carry three types of loads:

centrifugal forces of its own mass;

· pressure difference of the transported medium on the working and back sides of the blade;

reaction of the deforming main and cover discs.

In practice, loads of the second and third types are not taken into account, because these loads are much less than the loads from centrifugal forces.

In the calculation, the blade is considered as a beam working in bending. The approximate bending stress in the blade can be calculated by the formula:

s silt = = 779 kg/cm 2 ,

where R 1 and b 1 - the radius of the impeller at the suction and the thickness of the blade, respectively, mm.

Test calculation for the strength of the main disk of the impeller

When designing the impellers, the thicknesses of the disks are assigned by the designer with subsequent verification of stresses by calculation.

For single suction wheels, the maximum tangential stress can be checked using the formula:

s τ = kg/cm2

where G l - the total mass of the blades, kg;

δ / - disk thickness, mm;

n 0 - number of revolutions, rpm.

l = =110 kg,

where ρ = 7850 kg/m 3 .

Odds k 1 and k 2 are determined by the nomogram (Fig. 5).

Rice. 5. Nomogram for determining coefficients k 1 and k 2

The resulting stress should not exceed the yield strength for steel [ sτ] = 2400 kg/cm 2 .

6. Fan drive selection

To drive console-type fans, asynchronous electric motors of the 4A series and their analogues of other series are mainly used. To select an electric motor, the fan speed and its power are guided. At the same time, it is necessary to take into account the need for a power reserve in order to avoid engine failure during start-up, when large starting currents occur. The safety factor for general purpose fans =1.05¸1.2 is selected based on the fan power. Larger coefficient values correspond to lower power values.

For draft fans, the drive power is selected taking into account the pressure safety factors k d \u003d 1.15 and filing k n = 1.1. Engine power reserve k N=1,05.

The choice of electric motors is made according to catalogs and reference books. We choose the AIR180M4 electric motor with a rotation speed of 1500 rpm and a power of 30 kW.

Factory designation	Type of electric / motor	Installed engine power kW	Cons. power, kWt	Supply thousand m3/h	Pressure daPa	Dimensions (LхВхН), mm

VDN10-1500 rpm

7. References

1. Solomakhova T.S., Chebysheva K.V. Centrifugal fans. Aerodynamic schemes and characteristics: a Handbook. M.: Mashinostroenie, 1980. 176 p.

Vakhvakhov G.G. Energy saving and reliability of fan installations. M.: Stroyizdat, 1989. 176 p.

Aerodynamic calculation of boiler plants (normative method). / Ed. S.I. Mochan. L.: Energy, 1977. 256 p.

Draft machines: Catalogue. Sibenergomash. 2005.

Aliyev Electrotechnical reference book

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 purify the air from various impurities, metal and wood chips, dust and dirt, powerful ventilation units are most often used. 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 the design features and appearance of 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 domestic and 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. By combining two snails of different types 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 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, the “snail” is a plain-looking and rather large device that can ruin the overall design of the kitchen. 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 the question remains relevant, 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-made ventilation. So, you will need:

Frame. It can be bought at a 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 should be paid to the reliability of the fastening of the fan and the impeller. With strong air currents, these components can become loose and come off, which will invariably lead to damage to the ventilation. All parts, including the body, must be made of refractory materials.

Scheme of the ventilation "snail"

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

The so-called snail for ventilation may not always mean the same type of forced ventilation device - the main common features are the shape of the unit, but by no means the principle of operation and direction of the air flow.

Injectors of this type can:

radically differ in the principle of the arrangement 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 large solid fuel boilers, production shops and public buildings, but all this is below, and in addition - the video in this article.

mechanical ventilation

Note. Electric motor-driven blower / suction units, which are called "snails", are not suitable for any type of ventilation, as 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 refer to completely different ways of exchanging air, and some you may not even have heard of, but we will briefly consider only the most basic ones.
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 to operate using axial (axial), radial (centrifugal), diametrical (tangential) and diagonal fans. In addition, the exhaust and air supply can be carried out either in general or in local mode. That is, the air duct is brought to a certain 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 (Turkey) is a radial type exhaust snail 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 380m 3 /min of air with a temperature range from -15⁰C to +40⁰C, has an IP54 safety class.

The BDRS brand can have several sizes, the external rotary engine is made of galvanized steel and is protected on the side by a chrome grille, which prevents third-party elements from entering the impeller.

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

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

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

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

Any modification implies the possibility of turning the body to the right or left. This allows you to connect to existing 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 arrangement can be used, and its impeller in the form of forward-curved blades is made of galvanized steel. Rolling bearings increase the operational life of the unit, factory balanced turbines significantly reduce noise, and the protection level is IP54.

In addition, for the VSCUN, do-it-yourself speed control is provided 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 the main condition must be met without fail - their total power must not exceed the rating of the transformer.

Specifying a parameter	VCUN
Specifying a parameter	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 consumption maximum (m 3 /hour)	450	710	750	1540	1030	1950	1615	1900
Rotation speed (r/min)	1350	2730	1360	2820	1360	2800	1360	2800
Sound level at 3m (db)	60	65	62	68	64	70	67	73
Air temperature during transport maximum t⁰C	60	60	60	60	60	60	60	60
Protection	IP54	IP54	IP54	IP54	IP54	IP54	IP54	IP54