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Help inm suction mechanism design

  1. Jun 2, 2009 #1
    hey...I have to develop a suction mechanism for sucking air from a 20 meter high stack to the ground level and at 20lpm outlet flow rate. I dont know the difference between using a suction fan or a pump and which of the 2 would be better .also how to account for all the losses that will be there in the entire piping system?

    I would be extremely thankful if you could please explain and answer this and if it is not your specialisation then if you coul dplease forward it to the concerned person.
  2. jcsd
  3. Jun 4, 2009 #2


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    Staff: Mentor

    Welcome to the PF. What do you mean by suctioning air from a 20 meter high stack? What is the volume? Are you trying to pump down the pressure in that volume? To what pressure below atmospheric?

    Or are you just trying to create a 20LPM airflow out of a semi-open volume, to keep it at a constant negative pressure with respect to the ambient air pressure outside the volume?

    Can you please post more details about your specific application? It's hard to help you without those specifics.
  4. Jun 4, 2009 #3
    Sir my purpose is to take a sample of air from the stack and then mix it with ambient fresh air in desired proprortions so that the total flow rate is 20lpm and then use the mixed stream for sniffing as it is expecte dto be odorous. so either i collect and compress air from the stack and then mix it with fresh compressed air or i take online samples from the stack where the sampling point is located around 41' high and mix it with a stream of fresh air both the streams at same pressure to aoid back flow and all.

    so which one would you suggest and how to achieve the same?
  5. Jun 4, 2009 #4
    There's more to this that's needed. If this is a process stream stack than the stream must be known. If this is a gaseous stream then a 'whiffle tube' can be used. If this is a combination stream requiring catalytic cracking to produce the product there are a few more things to consider. Which is it?
  6. Jun 4, 2009 #5
    It is a gaseous stream coming from cold plasma unit and i want to make a setup for olafctmetry to estimate the odor levels and sir i have no idea what is a whiffle tube?
  7. Jun 5, 2009 #6
    Whiffle tube is an old saying for a gas draw off device within a pressure vessel. If you had to clean one during a 'turn around' that would be the only thing you would call it. It has many holes and is the equivalent of a whiffle ball turned into a tube but the holes vary in size as the column height increases.
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