Cooling tower noise control

1、 Analysis of noise sources in cooling towers:

A cooling tower is a mechanical equipment used in a circulating water supply system to reduce water temperature (usually 4 ℃ -6 ℃, and in industrial high-temperature cooling towers, the water temperature can be reduced to 10~C-15 ℃). Its working principle is that the cooling water in the collection pool at the bottom of the cooling tower flows down by gravity, and the water pump sends it to the condenser to absorb the heat released when the refrigerant condenses. This hot water is discharged from the condenser and sent to the top of the cooling tower, where it is sprinkled into water droplets and flows down through the packing material. When hot water falls, it comes into contact with a cooler airflow for heat exchange. At this time, some of the water evaporates, and most of it is cooled and flows back to the collection tank.
With the development of the economy, factories, restaurants, hotels, office buildings, and dance halls have sprung up like mushrooms after rain. Especially in the south where the weather is hot for a long time, cooling towers must be installed for central air conditioning cooling. In some concentrated areas of factories, there is a phenomenon where a building has more than ten or twenty cooling towers. In some mixed use commercial and residential areas, enterprises cannot be placed on rooftops or in their own floor space, and can only be placed on the ground. The strong noise and hot air from the cooling tower vents often disturb residents' peace. So the issue of cooling tower noise has become a hot topic of environmental complaints. After analysis and spectrum testing, the cooling tower noise is generated in the following aspects:

1. Fan noise

It is the main source of noise for mechanical ventilation cooling towers, which is aerodynamic noise, including turbulent noise and rotational noise. According to the theoretical analysis of aerodynamic noise sources, the sound intensity of turbulent noise is proportional to the sixth power of the relative velocity of the airflow and is also related to the shape of the blades, exhibiting continuous spectral characteristics. Rotating noise is generated by the pulsation of blades during rotation, which is related to the number of blades, gas flow rate, static pressure, etc. Its frequency spectrum exhibits narrowband low to medium frequency characteristics.

2. Water splashing noise

The operation of the fan generates noise from the intake and exhaust, as well as water spray noise. The fan radiates noise outward through the intake and exhaust ports and tower body. The exhaust noise is about 5-10dB higher than the intake noise (A), and its spectral characteristics are mainly low-frequency continuous spectrum, belonging to low-frequency noise. When circulating hot water falls from the water spraying device, it collides with the accumulated water in the water tray at the bottom of the tower, resulting in high-frequency noise. The size of the water spraying sound is related to the spraying height and the water flow rate per unit time.

3. Noise from gearbox and motor

The noise of the reducer is mainly generated during gear meshing, while the noise of the motor is electromagnetic noise and mechanical noise. The impact of these two types of noise sources on the surrounding environment can generally be ignored.

4. Pump noise:
The water pump is installed near the cooling tower for circulating cooling water and often resonates with the water pipe to produce high-frequency modulated noise. If the noise intensity is high, it needs to be treated together.

2、 The general measures for noise control are:

Control the noise source of the cooling tower, cut off the transmission path, and protect the victims. The noise from cooling towers affects the daily lives of residents, with a wide range of victims and high mobility. Measures to protect the victims are not feasible, and only measures to control the noise source and cut off the transmission route can be taken. In response to the noise characteristics of the cooling tower, the following control measures are taken:

1. Replace the ordinary motor blades with low-noise blades to fundamentally reduce the noise level from the source.

2. The noise from the exhaust outlet has a continuous frequency spectrum characteristic, and sound absorption treatment should be considered. Using waterproof sound-absorbing materials to create sound-absorbing channels, achieving the goal of noise reduction.

3. Avoid mechanical resonance and noise, and perform vibration reduction treatment on the hard connection of the cooling tower.

4. Add a quick filter filler to the water receiving tray to reduce water spray noise.

5. Surround the tower and water pump with waterproof and sound-absorbing barriers to cut off the path of noise transmission.
 
      

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