The working principle of the tunnel fan is basically the same as that of the turbo compressor. However, because of the low flow of gas and water, the change in operating pressure is not large. In general, it is not necessary to consider the change of the specific volume of the gas, that is, the gas is said to be unable to reduce fluid mechanics. Axial fans can be divided into two types: left-handed and right-handed. From the beginning of the side of the motor, the centrifugal impeller rotates clockwise and is called a right-handed fan, while it rotates in the opposite direction and is called a left-handed fan.
A tunnel fan is a foot-operated device that uses the type of mechanical kinetic energy to boost air pressure and transport gas. This is a drive fluid mechanics device. Tunnel fans are commonly used in processing plants, mining, tunnel construction, glass fiber reinforced plastic cooling towers, natural ventilation, ash removal and cooling of cars, boats and buildings; natural ventilation and air inlets of heating furnaces and industrial electric furnaces; Refrigeration and natural ventilation of electrical products; dryness and selection of cereals; the surge and promotion of wind tunnel sources and hovercraft.
The frequency band of the tunnel fan noise is a composite frequency band. The tunnel fan is the accumulation of the noise component of the blades according to the frequency and the broadband gas driving force of the optical fiber. The cutter head is defined by the above formula according to the frequency:
Fn = Nbn / 60Hz
Calculated in the formula:
B ----- Total number of cutter heads
N ----- fan speed, rpm
n ----- Number of pulse current: n = 1 (fundamental frequency), n = 2 (secondary pulse current)
The noise level of the tunnel fan noise is not only related to the structure of the fan, but also the working attitude (determined by the total working pressure and the exhaust air volume) between the two. Different series of products and different types of fans have different sound levels. The same fan has different sound levels under different working standards. When the fan is operating at a high efficiency point, the sound level tends to be low and easy to consume.
In order to express the noise characteristics of the fan, the definition of A level has already appeared. A sound level refers to the A sound level caused by the anesthesia machine with the enterprise water flow (1m / min) and the rated power of the enterprise motor (1mm water column). The same fan has different A-levels under different operating standards. At the point of high efficiency, it is lower than A sound level. The characteristics of the proportion A of the fans of different series under the rated value standard qualitatively analyze the noise level and product quality of the fan series. Therefore, at this stage, the A level is used as the limit index value of the fan noise. Different types of fans in the same series are similar to A-level speakers. The higher the precision of the production and processing of the fan, the better the hydrodynamic characteristics and the lower the A sound level.
Generally speaking, the sound level of the front blade axial fan is lower than 2dBA; the rear flat blade centrifugal fan is lower than 30dBA airfoil centrifugal fan, lower than 25dBA; the axial fan is lower than 38bBA. Under different working standards, the sound level of the tunnel fan noise is calculated by the following formula:
LA = LSA10LgQPdBA
Calculated in the formula:
La ---- sound level of fan channel (or entrance), dBA;
Lsa ---- Fan A (or vent) accounts for A sound level, dBA;
Q ---- Exhaust air volume, meter 3 / min;
P ---- Centrifugal fan motor rated power, mm water column.