need help
 

i bought a HEPA filter and the tag came with specification "RESISTANCE 150pa and TESTED 0.45m/s. what does that mean,and does that tell any the blower i must use?

Sounds like it's the lab test for how much it can handle.
pa is the symbol for pascal unit which is a unit for pressure. (force per unit area)
m/s stands for meter per sec. (speed and velocity)

Thanks Melody, for the explanation.

The filter size 530mm x 530mm x 69mm and the worked out matching blower was 300cfm / 500m³/h, i wonder i am right, anyone? The calculation was based on the following link:
Laminar Flow Hood - Build a HEPA filter flowhood | Fungifun

If I remember from many years ago and a far different place......

530mm = 1.74 ft so (530 X 530) sq mm = 3.02 Sq ft the area of your filter

There are two common uses of HEPA filtered air: to provide a continual flush of sterile air between and around samples being worked on to prevent cross-contamination, and to provide positive overpressure of sterile air to a glovebox, where one sample at a time is usually worked on so contamination from the outside, rather than cross contamination is the biggest risk.

In an open front laminar flow hood, your blower (unrestricted) pushes 300 cfm and your HEPA filter has a static resistance of 150pa. The Lotte & Thomas site shows that resistance as a 60% reduction in airflow. Your blower would deliver about 120 cfm with just the HEPA in line. If you use a prefilter, it will decrease the velocity again, but not as much. Because prefilters are cheap to replace and a good HEPA is not, I strongly recommend a prefilter. The 120 cfm would be distributed across 3 sq ft, so you would have 40 ft/m air velocity across the entire front opening (assuming it is the same size as the filter). Unfortunately I don't remember the standard for face velocity, but this seems low.

The face velocity of an open HEPA filter hood is critical to keep the work area flushed with clean air. An open HEPA hood is most convenient if you are bringing items into the work area and want to prevent cross contamination from one sample to the next (there is a continual flow out of clean air). If you want a glove box arrangement, the HEPA air flow can be much lower. THe filtered air pressurizes the glove box and any voids or leaks leak out to prevent contamination. If you are working on one sample at a time, this is a good and cheaper way.

Both methods need good technique to prevent contamination.

The above are my best recollections of how to do this going back almost 40 years. After a few successful calculations and purchases, my staff grew, and I no longer had to do the math. It's been an interesting exercise, and things keep coming back to me - if you have any other ducting, elbows or restrictions, they all add to the static loss. As I remember there are tables in engineering texts with those values. Another practical concern is the HEPA itself - take great care to protect it. If any damage is done to the surface, the air will flow through the lower resistancve damaged area. Even though the damage might only affect 1% of the surface area, it can have a significant effect on the quality of air pushing through, as well as destroying the "laminar curtain" of air moving at the same velocity across the entire work area.

Hope this helps a bit, and hope even more that it is accurate. Please, if anyone has more current experience feel free to correct the numbers.

Bobin, thanks for the explanation.