3D filtration principles

Summary

This video explains how filters in compressed air systems remove contaminants like dust and oil aerosol. It debunks the misconception that filters work by trapping particles larger than their pores. Instead, three filtration mechanisms are at play: inertial impaction captures larger particles, interception traps medium-sized particles, and diffusion removes the smallest particles. Together, these mechanisms ensure effective filtration by capturing particles of varying sizes through different physical processes, resulting in high filter efficiency.

Takeaways

• 😀 Contaminants like dust and oil aerosols are common in compressed air and can affect performance.
• 😀 Contaminants enter the air system through intake air, impurities during installation, or compressor lubrication.
• 😀 Filters are installed after the compressor to remove contaminants from the airstream.
• 😀 Filtration is often misunderstood as being based solely on particle size and filter pore size, but it involves multiple mechanisms.
• 😀 The first filtration mechanism is inertial impaction, where larger particles collide with filter fibers due to their inertia.
• 😀 Inertial impaction becomes more important as particle size increases.
• 😀 The second mechanism, interception, captures particles by their size and proximity to the filter fibers.
• 😀 Interception becomes more important as particle size increases but remains relevant for smaller particles too.
• 😀 The third mechanism is diffusion, which targets the smallest particles through Brownian motion, making them collide with filter fibers.
• 😀 Diffusion is most effective for the smallest particles and becomes more important as particle size decreases.
• 😀 The combined action of inertial impaction, interception, and diffusion results in the total filter efficiency.

Q & A

What are some common contaminants found in compressed air?

Compressed air contains contaminants like dust, oil aerosol, and particles from the intake air, installation, and the lubrication of the compressor.

What is the role of filters in compressed air systems?

Filters are installed after the compressor to remove particles from the air stream, ensuring cleaner air by trapping contaminants such as dust and oil aerosol.

How are the glass fiber layers in the filter structured?

The glass fiber layers in the filter consist of very thin fibers that are randomly distributed and oriented in all directions.

Is it true that filters work by trapping particles larger than the filter’s pores?

No, this is a misconception. Oil aerosol and dust particles are much smaller than the media pores, so they do not get trapped by size alone. Instead, different filtration mechanisms are at work.

What is inertial impaction in the filtration process?

Inertial impaction occurs when heavier particles do not follow the gas flow streamlines due to their large inertia. They travel in a straight path until they collide with a fiber and are removed from the air.

How does the mechanism of interception work?

Interception occurs when particles, lighter than those in inertial impaction, follow the gas streamlines. If their radius is larger than the distance between the streamline and the fiber, they hit the fiber and are captured.

What is diffusion, and how does it contribute to filtration?

Diffusion is the process where small particles move randomly due to collisions with gas molecules, a phenomenon known as Brownian motion. The smaller the particle, the higher its movement freedom, making it more likely to collide with and be captured by a fiber.

Which filtration mechanism is most important for larger particles?

Inertial impaction is most important for capturing larger particles, as their inertia prevents them from following the gas streamlines, causing them to collide with the filter fibers.

Which filtration mechanism is most effective for smaller particles?

Diffusion becomes more important for capturing smaller particles, as these particles have more freedom of movement and are more likely to encounter the filter fibers due to their random movement.

How is the overall filter efficiency determined?

The total filter efficiency results from the combination of the three filtration mechanisms: inertial impaction, interception, and diffusion, each handling particles of different sizes.