Airflow in cleanroom: Laminar flow and Turbulent flow

  • 02, 08, 2021

To construct a clean environment, we not only put clean and filtered air into cleanroom but also what happens to the airflow inside cleanroom.

In general, the air in a cleanroom comes into 2 types: Turbulent flow and laminar flow. 

1. Turbulent flow in cleanroom

Turbulent flow is by nature chaotic and unconfined. This means that the air mixes and swirls, perhaps forming eddies and vortices.

The essence of turbulent flow is its lack of unidirectionality. Hence, turbulent flow is also called non-unidirectional or multidirectional flow. 

The main problem with turbulent air, with regard to contamination control, is that it can reduce the cleaning efficiency of our clean environment. To understand this, we must keep in mind that even the cleanest facilities will have a definite particle generation rate associated with the inside of the cleanroom. The incoming clean air must be able to sweep out this contamination. The presence of turbulence within the room will result in the removal of contamination being effectively slowed down or even stopped in some areas.

2. Laminar flow in cleanroom

Laminar flow (or unidirectional flow) is best described as in which the streamlines remain parallel and uniform.

Unidirectional flow is obviously the best choice for clean areas.

In the absence of any disturbing influence, like a rapidly moving object in the airflow, the air exiting from an opening, such as our HEPA filter, will be laminar if we limit its velocity to the range of 0.25 to 0.75 meters per second (approximately). 

The air velocity usually chosen for cleanrooms is around 0.45 meters per second (with a 20 percent tolerance). This unidirectional air will effectively sweep out contamination from our clean volume. 

Source: "Cleanroom" book

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