NEWS

Marine silencers are mainly divided into dry silencers and wet silencers, which are two different types of soundproofing devices. Below are their main differences:

Working Principle

l Dry Silencer

① Resistive Muffling: This uses porous sound-absorbing materials, such as fiberglass or rock wool. When sound waves enter the silencer, they cause the air molecules in the absorbent material to vibrate. Through friction, sound energy is converted into heat energy and dissipated, thus weakening the sound wave intensity. For example, resistive silencers with sound-absorbing materials are used in some air conditioning ducts to reduce airflow noise.

② Reactive Muffling: This works by altering the pipe's cross-sectional area, shape, or adding resonant chambers, which causes the sound waves to reflect, interfere, and cancel out or weaken certain frequencies during propagation. For instance, some expansion chamber structures in car exhaust pipes use the principle of reactive muffling.

③ Impedance Composite Muffler: This combines the principles of both resistive and reactive muffling, integrating the advantages of both. It effectively absorbs mid-to-high frequency noise and can also suppress low-frequency noise to some extent.

l Wet Silencer

This works primarily based on the difference in sound wave propagation between gas and liquid. When noisy airflow passes through the wet silencer, the sound waves in the airflow interact with the particles or liquid film in the liquid. The liquid absorbs and takes in the sound wave energy, causing the sound to gradually decay. Eventually, the sound energy is converted into heat, achieving the muffling effect. Additionally, the liquid can also filter impurities, such as dust, in the airflow.

Structural Features

l Dry Silencer

① Resistive Dry Silencer: Typically composed of an outer shell and internal sound-absorbing materials. The sound-absorbing material is usually fixed to the inner walls of the airflow channel or arranged in a specific manner within the pipe, such as in the form of sound-absorbing plates or panels.

② Reactive Dry Silencer: Mainly composed of pipes and chambers of different shapes and sizes. It achieves sound wave reflection and interference through carefully designed structures. Common types include expansion chamber and resonant chamber designs.

③ Impedance Composite Dry Silencer: Combines both resistive and reactive components, making the structure more complex. It may include sound-absorbing materials, expansion chambers, resonant chambers, perforated plates, and other components.

l Wet Silencer

Generally consists of an intake pipe, silencing chamber, exhaust pipe, and liquid storage device. The silencing chamber is filled with liquid, such as water, oil, or other special soundproofing liquids. The intake pipe directs the airflow from the noise source into the silencing chamber, where the airflow fully interacts with the liquid to achieve noise reduction. The treated air is then discharged through the exhaust pipe.

Performance Characteristics

l Dry Silencer

① Noise Reduction Frequency Characteristics: Resistive Dry Silencer: Effective at reducing mid-to-high frequency noise, but less effective for low-frequency noise. Reactive Dry Silencer: Suitable for reducing both mid and low-frequency noise. Impedance Composite Dry Silencer: Offers good noise reduction performance across a wide frequency range.

② Pressure Loss: Resistive Dry Silencer: Generally has higher pressure loss, especially when the airflow velocity is high. Reactive Dry Silencer: Has relatively low pressure loss. Impedance Composite Dry Silencer: Has pressure loss between that of the resistive and reactive types.

③ Applicable Environments: Suitable for various dry and clean environments, as well as places with fire and explosion protection requirements, such as power plants, boiler rooms, and HVAC systems.

l Wet Silencer

① Noise Reduction Effect: Effective at reducing mid-to-high frequency noise. In some cases, it performs better than dry silencers for low-frequency noise, making it effective at reducing noise pollution.

② Pressure Loss: Typically has lower pressure loss than dry silencers. The resistance to airflow passing through the muffler is lower, so it does not have a significant impact on system operation.

③ Applicable Environments: Suitable for harsh environments with high temperatures, high humidity, dust, or oil contamination, such as exhaust systems in industrial furnaces and incinerators. It is also commonly used in places that require fire and explosion protection because the liquid has some flame-retardant and explosion-proof properties.

Performance and Application Scenarios Comparison

Comparison Points	Dry Silencer	Wet Silencer
Noise Reduction Effect	Better control of mid-to-low frequency noise (reactive structure)	More balanced noise reduction across the entire frequency range (liquid + sound-absorbing material)
High Temperature Resistance	Relies on metal materials (e.g., stainless steel) for high temperature resistance; prolonged exposure to high temperatures may affect lifespan	Liquid cooling can lower exhaust temperature, making it suitable for high-temperature environments
Weight and Volume	Compact structure, lightweight (suitable for space-constrained vessels)	Requires a water tank or circulation system, larger in size
Maintenance Cost	Simple maintenance (no liquid medium handling required)	Requires regular replacement of water or antifreeze, and seal checks
Applicable Scenarios	High-speed vessels, small generators (balance between speed and noise reduction)	Large engines, boiler exhaust systems (requires efficient noise reduction and cooling)

Selection Recommendations

l Suitable Situations for Dry Silencers:

① Space Constraints or Need to Control Equipment Weight: Such as high-speed passenger vessels, small boats, or compact workboats (e.g., tugboats).

② Lower Exhaust Temperature or Intermittent Operation: Such as auxiliary engine generators.

③ Limited Budget and Predominantly Mid-to-Low Frequency Noise: Such as inland cargo ships.

④ Clear Requirements for Spark Extinguishment: Such as oil tankers.

l Suitable Situations for Wet Silencers:

① Continuous High Load Operation: Gas turbines or high-load diesel engines (e.g., main engine exhaust).

② Need to Reduce Both Noise and Exhaust Temperature: Such as in boiler systems.

③ High Demand for Noise Reduction Across the Full Frequency Range: Such as research vessels or cruise ships.