In a cleanroom, even the smallest particle can pose significant risks. Particle deposition occurs when airborne particles come to rest on surfaces. Particle deposition in cleanrooms can compromise sensitive processes, contaminate products, and affect the precision of experiments.
Have you ever wondered how tiny particles floating in the air end up settling on surfaces like tables or walls? It’s actually a bit complex, but let’s break it down into simple terms. For example: Did you know that understanding the air movement inside your cleanroom can help toward removing this risk?
Here’s a rundown of the main ways particles can end up on surfaces:
Gravity Pulls Them Down (Gravitational Settling)
Just like how gravity pulls a dropped object to the ground, it also pulls particles down onto surfaces. Bigger particles fall faster. For example, a tiny particle might drift down very slowly, but a larger one will fall much quicker and land on surfaces more easily.
Turbulence Blows Them Down (Turbulent Deposition)
Imagine you’re stirring a drink and notice how the liquid swirls around. The same kind of swirling happens in the air, creating turbulence. When air is turbulent, particles get pushed around and can end up sticking to surfaces. The stronger the turbulence, the more particles end up settling down.
Static Electricity Attracts Them (Electrostatic Attraction)
You know how a balloon sticks to your hair when you rub it? That’s static electricity in action. Similarly, particles in the air can have static charges, which can make them stick to surfaces that have the opposite charge. In places where cleanliness is crucial, efforts are made to reduce static charges to avoid attracting too many particles.
Tiny Particles Bounce Around (Brownian Motion)
For very small particles, less than half a millionth of a meter (0.5µm), they don’t just float around smoothly. They bounce around randomly due to collisions with air molecules. This random movement can make them collide with surfaces and stick.
Filters Catch Them (Impaction)
Think of air filters like catching fish with a net. As air flows through a filter, bigger particles are too heavy to follow the airflow and get trapped on the filter. This helps to clean the air by removing those particles.
Close Encounters (Interception)
Sometimes, particles get very close to a surface, like a filter fiber. If they get close enough, they stick to it. This is similar to how a small object might stick to a sticky note if it gets close enough.
Cool Surfaces Attract Tiny Particles (Thermophoresis)
When a surface is cooler than the surrounding air, it can attract tiny particles. However, this only works well for really small particles and isn’t very effective if the surface is not cold enough. In most cleanroom environments, surfaces are not significantly cold, making this mechanism less relevant.
Particles Get Stuck in Quiet Areas (Turbophoresis)
In areas where there is less air movement, particles can get trapped because there isn’t enough turbulence to push them away. These quiet, low-turbulence zones can act like traps for particles. This mechanism can contribute to particle deposition in areas with varying turbulence levels.
Conclusion
Each deposition type plays a role in particle management, and their significance varies based on particle size and environmental conditions. Understanding these mechanisms helps to design effective cleanroom environments and air filtration systems to maintain particle cleanliness and control.
To go in-depth into the science behind particle deposition click here.
