Now exhaust fans are widely used in many industries, and the types of exhaust fans are gradually increasing. Generally, axial flow exhaust fans and centrifugal exhaust fans are often used. How to distinguish these two types of fans? The most common axial fans are household electric fans and external fans of air conditioners; The centrifugal fan is the fan in the range hood and cabinet air conditioner. In terms of function, it can be divided into induced draft fan and blast fan, which can be realized by any type of fan.
The flow of the exhaust fan refers to the volume of gas flowing through the fan in unit time. The units are m3/h, m3/min and m3/s. In China, it is customary to use m3/h for ventilators, while m3/min for blowers, and m3/s for high-voltage electrostatic fume purifiers. However, m3/s is mostly used in the design and performance calculation of ventilators. It must be noted that the volume flow of the fan refers to the volume flow at the "inlet" of the fan. Because the pressure of the fan on each flow passage section is different, the volume flow through each flow passage section will also be different.
The total pressure of a fan is defined as the difference between the total pressure on the fan outlet section and the total pressure on the fan inlet section. The total pressure of air flow at a point or a section is equal to the sum of dynamic pressure and static pressure at that point or section.
The rotating speed of the fan refers to the rotating speed of the fan impeller in unit time, generally referred to as the angular speed, which is usually expressed in n and is expressed in revolutions per minute (r/min).
Shaft power The shaft power of a fan refers to the actual power required by the fan. It includes the internal power rate of the exhaust fan and the mechanical loss of the bearing and transmission device. The shaft power is also called the input power of the fan, which is actually the output power of the motor.
Fan efficiency
(1) Total pressure internal efficiency of fan eta;%* p%*pin%*b
Total pressure internal efficiency of fan eta;%* P% * pin% * b is equal to the ratio of total pressure effective power and internal power of the fan.
(2) Static pressure internal efficiency of fan eta;%* p%*ps.in%*b
Static pressure internal efficiency of fan eta;%* P% * ps.in% * b is equal to the ratio of static pressure effective power and internal power of the fan.
The total pressure internal efficiency and static pressure internal efficiency of the fan are important parameters to characterize the aerodynamic performance of the fan.
(3) Total pressure efficiency of fan eta;%* p%*ptf%*b
Total pressure efficiency of fan eta;%* P% * ptf% * b is equal to the ratio of total pressure effective power and shaft power of the fan.
(4) Static pressure efficiency of fan eta;%* p%*psf%*b
Static pressure efficiency of fan eta;%* P% * psf% * b is equal to the ratio of static pressure effective power and shaft power of the fan.
Closed static pressure (BTSP)
Closed static pressure of fan refers to the static pressure when the fan outlet is completely closed without gas movement. Fan full open gas flow (WOCMS)
The gas flow at the full opening of the fan is also called open CMS (WOCMS), that is, the flow at the full opening of the fan. At this time, the static pressure of the fan is zero.
The operating flow and pressure range of the fan determined by the fan manufacturer to obtain satisfactory results when the fan is operating.
Typical fan application range:
Forward curved centrifugal fan: 30% - 80% WOCMS
Bench centrifugal exhaust fan: 40% - 85% WOCMS
Radial centrifugal exhaust fan: 35% - 80% WOCMS
The exhaust fan is a kind of machine that converts the mechanical energy of the prime mover into gas conveying and giving gas energy. It is an indispensable mechanical equipment in the thermal power plant, mainly including the forced draft fan, induced draft fan, primary air fan, seal fan and powder exhauster. The power consumption accounts for 1.5%~3.0% of the power generation of the power plant. In the actual operation of thermal power plants, the fan, especially the induced draft fan, has a high failure rate due to poor operating conditions. According to relevant statistical data, the induced draft fan has an average failure of 2 times a year, and the forced draft fan has an average failure of 0.4 times a year, resulting in unplanned shutdown or load reduction operation of the unit. Therefore, it is the guarantee for the continuous and safe operation of the power plant to quickly determine the cause of the fault during the operation of the fan and take effective measures to solve it. Although there are many types of failures of the exhaust fan and the causes are very complex, according to the investigation of the actual operation of the power plant, many failures of the fan are: bearing vibration, high bearing temperature, jamming of moving blades, and maloperation of the protection device.
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