Noise of blower regenerative and Its Control Technology
The noise spectrum of high-pressure fan is a composite spectrum, which is the superposition of blade passing frequency and broadband aerodynamic noise components. The passage frequency of the blade is determined by the following formula:
FN = Nbn/60 Hz
B - - - Number of blades
N - --- Turn, turn/minute of high-pressure ventilator
N - - - Homophonic ordinal number: n = 1 (fundamental frequency), n = 2 (second homophonic)
The noise level of high-pressure fan is not only related to the structure of high-pressure fan, but also to its working state (determined by total pressure and air volume). Different series and models of high-pressure fans have different sound levels. The sound level of the same high-pressure fan is different under different working conditions. When the high-pressure fan works at the highest efficiency point, the sound level is usually low.
In order to better characterize the noise performance of high-pressure fans, the concept of class A has emerged. Ratio A sound level refers to the A sound level produced by a high-pressure ventilator under unit flow rate (1 m/min) and unit full pressure (1 mm water column). The sound level A of the same high-pressure fan is different under different working conditions. At the highest efficiency point, it is lower than A sound level. The noise level and product quality of different series of high-pressure fans are characterized by their A sound level at rated working conditions. So at present, the ratio A sound level is often used as the noise limit index of high-pressure fan at home and abroad. The sound level of the same series of different types of high-pressure fans is similar to that of A. The higher the processing accuracy of high-pressure fan, the better the aerodynamic performance, and the lower the sound level of A.
Generally speaking, the forward blade centrifugal high-pressure fan has a sound level lower than 2dBA; the backward plate blade centrifugal high-pressure fan is lower than 30dBA blade centrifugal high-pressure fan, lower than 25dBA; and the axial high-pressure fan is lower than 38bBA. Under different working conditions, the noise level of high-pressure fan is determined by the following formula:
LA = LSA + 10LgQP dBA
La - A sound level, dBA, at the inlet (or outlet) of the high-pressure fan;
Lsa - the ratio A sound level of the intake (or outlet) of the blower regenerative, dBA;
Q - Air volume, m 3/min;
P - - blower regenerative full pressure, millimeter water column.
The common method to control the noise of high-pressure fan is to install Resistance Muffler at the inlet and outlet of high-pressure fan. For the occasion with higher noise reduction requirements, the sound insulation box can be used, and the shock absorber can be placed between the unit and the foundation. By adopting the above methods, the obvious effect of noise reduction can generally be obtained.
There are many noise control equipment factories in China, which can provide noise eliminators, noise isolation boxes and shock absorbers for various types of high-pressure fans. The noise problem of high-pressure fan can be effectively controlled technically in our country, and low-noise high-pressure fan has begun to appear.
However, for mufflers of blower regenerative with special requirements, such as water-proof, moisture-proof, high temperature resistance or dust-proof, there are still many research work worth carrying out.