Within industrial plants, while designing solutions for noise control, it is crucial to estimate how loud a specific noise source might be, especially in absence of actual measurements for any specific source.
But first, it is imperative to identify which are main noise sources and their characteristics. The goal of this article is to examine the main noise sources from several mechanical systems in industrial plants.
Main noise sources
1. Fan noise
Industrial fans come in different types with distinct noise features:
- Centrifugal fan with airfoil blades: used in large heating, ventilation, and air conditioning systems for clean air.
- Centrifugal fan with backward curved blades: used for general ventilation and air conditioning, with higher efficiency.
- Centrifugal fan with radial blades: commonly used in material handling systems.
- Centrifugal fan with forward curved blades: used for low-pressure and low-speed applications like home air conditioning.
- Tubular centrifugal fan: used in heating and ventilation for low-pressure return-air systems.
- Vaneaxial fan: suitable for medium to high-pressure applications but tends to be noisier.
- Tubeaxial fan: used in low to medium-pressure applications.
- Propeller fan: suitable for handling large volumes of air, used in roof exhaust systems and cooling towers.
2. Electric motor noise
While individual electric motors are not usually very excessive, the noise can add up when managing different machines together. Various factors contribute to motor noise, including windage noise from cooling fans, rotor-slot noise, rotor-stator noise, magnetic flux changes, dynamic unbalance, and bearing noise.
3. Pump noise
Pump noise comes from hydraulic and mechanical sources. Key noise sources include cavitation, fluid pressure fluctuations, impact on solid surfaces, and rotor imbalance. Proper vibration isolation can reduce structure-borne noise from pumps.
4. Gas compressor noise
Gas compressors belong to the category of machinery where it is crucial to prioritize efficiency and durability over noise reduction. Many gas compressors are not designed with low noise emission as the primary design criterion. Therefore, typically, noise control measures are implemented post-construction. The variables influencing noise levels encompass the compressor’s power input, the turbulence of the fluid, and the nature of the gas being compressed.
5. Noise from gas vents
One of the more serious noise problems in industrial plants is the noise produced by the discharge of air, steam, or process gas into the atmosphere. Blow-off nozzles, steam vents, and pneumatic control discharge vents are some examples of noisy venting situations. Noise from these vents results from turbulent mixing, and the frequency of the noise depends on the size of the turbulent eddies.
6. Valve noise
Valves and regulators used with steam and gas lines can be a significant source of noise. There are two primary sources of noise generated by valves: (a) mechanical noise generation and (b) fluid noise generation, either hydraulic for liquids or aerodynamic for gases.
Mechanical noise comes from pressure fluctuations and fluid impingement, while fluid noise is either hydraulic or aerodynamic. Valve vibration noise can indicate potential issues with the valve.
7. Air distribution system noise
In heating, ventilation, and air conditioning (HVAC) systems, noise can be transmitted from the air-handling unit into the duct system. Additional noise may be generated as air flows through various components like elbows, fittings, grills, and diffusers.
Measures for noise control
Understanding and managing these different noise sources is crucial for maintaining a comfortable and safe working environment in industrial plants.
To effectively manage noise as it travels from its source to the receiver, typically a worker, a careful consideration of certain procedures is imperative in order to select the most suitable infrastructure within the industrial plant. Among the most proficient soundproofing procedures are:
- Employing Vent Silencers (for valves and tanks) designed to lower the noise levels produced by exhaust piping for pressurized gaseous fluids when vented to the atmosphere.
- Utilizing Acoustic Barriers, whether in the form of single walls, partial enclosures, or full enclosures for entire pieces of equipment.
- Installing Enclosures around noisy components within machinery.
- Implementing either Reactive or Dissipative Mufflers: the former for addressing low-frequency noise or smaller exhausts, and the latter for dealing with high-frequency noise or larger diameter exhaust outlets.
- Incorporating In-line Plenum Chambers or lined ducts into air handling systems.
- Managing reverberation by adding sound-absorbing materials to spaces with excessive reflected noise. It is important to note that this approach may not significantly affect the direct sound reaching the receiver.
- Exploring active noise control techniques, which involve manipulating the reflection, suppression, or absorption of noise emitted by an existing sound source through the use of one or more secondary or control sources.
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