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一、PURPOSE

Centrifugal fan is generally used for indoor ventilation of large buildings such as factories, and for high pressure forcible ventilation of boilers and forging boilers and other occasions of materials handling. Types of gas handled by centrifugal fan is air or other non-explosive and non inflammable gas and gas non-corrosive to steels. Stickum should not be contained in gas, dust and hard corpuscular matter contained should not be larger than 150mg/m3. Temperature for gas handling should not exceed 80°C。

二、STRUCTURAL FEATURE

Centrifugal fan generally consists of parts of air inlet, impeller, scroll case, outlet, gearing device, base and motor.

Sketch map of structure of centrifugal fan

(1) inlet: inlet is made into an integer and set up at the side of scroll case of fan. Shaped conductor of axial cross section of inlet is streamline, the current can enter impeller equably so as to reduce flow loss and improve efficiency of impeller.

(2) Impeller: impeller is the most important part of centrifugal fan, its function is to invert mechanical energy into gaseous static pressure energy and kinetic energy. Impeller generally consists of front panel, blade, back panel and axial panel (wheel hub). Through balanceable emendation, operation will be smooth, and gas performance is good.

(3) Scroll case: scroll case is the passage of gas current, shaped conductor is usually log spiral with effect of current collection and guidance to outlet. Scroll case also has certain effect of pressure extension.

(4) outlet: a passage for gas to flow out of fan. Outlet is drilled with bolt hole and can be connected with air pipe.

(5) Gearing device: consists of principal axis, bearing housing, rolling bearing, pulley or clutch. One end of principal axis is connected with impeller, the other end is connected with pulley or clutch.

三、VERSION

Centrifugal fan is divided into dextral fan and laevogyrate fan according to rotary direction of impeller. It is called dextral fan and expressed with right if front view from one side of motor or gearing device finds impeller rotates clockwise, and called laevogyrate fan and expressed with left if front view from one side of motor or gearing device finds impeller rotates counterclockwise.

Location of outlet of centrifugal fan is expressed with the angle of outlet of mantle. The adjustment scope of location of outlet of centrifug

Common driving types of fan are as follows:

Driving Type A: centrifugal fan is not set up with gearing device, motor and impeller drive in connection.

Driving Type C: centrifugal fan is set up with gearing device, impeller and pulley are respectively located at both ends of gearing device, motor drives through pulley.

Driving Type D: centrifugal fan is set up with gearing device, impeller and clutch are respectively located at both ends of gearing device, motor drives through clutch.

(Remarks: Figuration of fan and its installation chart are shown on the table below.)

四、PERFORMANCE SELECTION

Parameters in the fan performance table refers to fan performance under standard status, which is: atmospheric pressure Pa=101325Pa, atmospheric temperature fa=20°C, relative humidity hu =40%, air density p =1.2 kg/m3.

In case of non-standard status or variable fan's speed, it is necessary to invert performance under non-standard status into performance under standard status, and then select fan according to inverted performance. The inversion formula is as follows:

五、INSTALLATION AND OPERATION

Centrifugal fan is set up with monolithic base and it is not necessary for the user to make and install base by himself. In installation, the user just needs to place the monolithic fan on the ground and fix it with anchor screw. The user may also select special absorber of this factory and place monolithic fan on level ground through absorber, and anchor screw is not necessary, easy for installation and adjustment.

In fan's operation, phenomena of over-sufficient or insufficient runoff often occur mainly because of inaccurate calculation of resistance of pipe network, or variable resistance of pipe network. In fan's operation, the runoff gradually decreases in a long period of time, or suddenly decreases in a short period of time, mainly because of blockade of pipe network.

When the fan is newly installed, phenomena of over-sufficient or insufficient volume flow occur in formal operation mainly because of the following:

1. Difference between actual value and calculated value of pipe network resistance is too big. It is known from formula of regular pipe network characteristics of P=KQ2 that if the actual value of K, the coefficient of pipe network characteristics, is less than the calculated value, the volume flow will increase, rf the actual value of K is more than the calculated value, volume flow will decrease.

2. In selection of fan impact of , warp of total pressure value of fan itself is not considered. When the actual total pressure of fan is positive warp, volume flow will increase, and when the actual total pressure of fan is negative warp, volume flow will decrease. Warp of volume flow of fan can be eliminated through the following methods:

(1) Adjusting volume flow with throttling gear, for example, with air damper or shutter.

(2) Changing speed adjustment volume flow of fan's impeller.

(3) Replacing with adjustment volume flow of fan with higher pressure or lower pressure.

(4) Changing adjustment volume flow of pipe network resistance. It is necessary to point out: throttling gear is generally adopted to adjust volume flow of fan. But when the actual volume flow is much more than the required volume flow, it will cause much waste of electric power and will be very uneconomical. If possible, reduction of fan speed or replacement of fan with lower pressure should be adopted. When throttling gear is in full operation, if volume flow is still too small, it means that the throttling gear is out of effect, and it is necessary to change pipe network to reduce resistance so as to increase volume flow. It is also possible to adopt methods of increasing speed of fan impeller or replacing with fan with higher pressure. However, the maximum speed of fan should not exceed the maximum speed in the performance table and it is necessary to calculate motor power.