28-07-2012, 10:28 AM
Noise reduction in blower
Blower.pptx (Size: 1.34 MB / Downloads: 59)
Types of fans
Centrifugal Fans: As the name suggests, the centrifugal design uses the centrifugal force generated by a rotating disk, with blades mounted at right angles to the disk, to impart movement to the air or gas and increase its pressure. The assembly of the hub, disk and blades is known as the fan wheel, and often includes other components with aerodynamic or structural functions. The centrifugal fan wheel is typically contained within a scroll-shaped fan housing, resembling the shell of the nautilus sea creature with a central hole. The air or gas inside the spinning fan is thrown off the outside of the wheel, to an outlet at the housing's largest diameter. This simultaneously draws more air or gas into the wheel through the central hole
Working to minimize it
How to Minimize Fan Noise
Reduce system impedance at the inlet and outlet ports. If a large part of the fan's flow potential is used up by the impedance of the inlet and outlet, a larger, faster, noisier fan will be required.
Avoid obstructions to the airflow, especially in the critical inlet and outlet areas. When turbulent air enters the fan, noise is increased by as much as 10 dB, usually in a discrete tone form that is particularly annoying.
Use a larger, slower fan rather than a faster, smaller version whenever possible. Often, this solution will produce less noise for the same airflow.
Relax the temperature rise limits where possible, to reduce the airflow required. This will allow you to use a smaller, slower fan that produces less noise.
Isolate the fan to avoid vibration transmission. Because fans operate at a low frequency and are light in weight, vibration isolators must be soft and flexible. Since the transmission is dependent on the system, trial and error is the best approach to a quiet system/fan interaction. In systems that require 20 CFM or less, cabinet vibration is the predominant source of noise, and isolation of the fan is the only practical solution.
Cooling fan noise is expressed in decibels (dBA). The dBA rating is determined directly by a sound level meter equipped with a filtering system which de-emphasizes both the low and high frequency portions of the audible spectrum. This measurement is recorded at a distance of 1 meter from the source.