Overview:

1. What is Laminar Flow(Unidirectional Air Flow)?: In the context of a Biosafety Cabinet or Clean Bench Laminar flow or more accurately 'Unidirectional Air Flow' is defined as airflow in which the entire body of air within a designated space is uniform in both velocity and direction. 

*The term Laminar Flow has some very specific definitions within the world of fluid dynamic and generally for the purpose of creating a contamination free area or workspace we are not producing true Laminar Flow so instead we use the term Unidirectional Air Flow which doesn't have all of the same baggage... 

2. What is a Laminar Flow hood and why is it used?: A Laminar Flow Hood uses a blower fan to push air through a HEPA filter and across/over a workspace at a uniform rate and direction. This provides a sterile environment in the workspace and helps to substantially reduce the risk of contamination.

3. What are the 3 major components of a Laminar Flow hood?:

  1. HEPA filter rated 99.99% efficiency @ .03 Micron and pre-filter
  2. Blower fan with sufficient power for filter 
  3. Frame to hold it all together

4. Design Considerations/Background

  • Every filter has a static pressure which serves as 'resistance' against airflow
  • Different filters will have a different static pressure value at the working point
  • Working point: is where the amount of air flowing through the filter is sufficient to meet the requirements of unidirectional airflow
  • Static pressure is often expressed in Inches of Water Column(In. WC) or in SI units Pascals (Pa)
  • 1"WC = 248.84 Pa
  • Each filter has a data sheet where you can find the static pressure & working point. 
  • Before air enters the blower it usually is pre-filtered by a furnace filter or some filter with a static pressure @ working point of  ~0.2"WC (50Pa) generally.

5. *IMPORTANT* Calculations:

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