Results 1 to 7 of 7

Thread: Venturi Ejector Air Flow Mechanics

  1. #1
    Associate Engineer
    Join Date
    Dec 2019
    Posts
    6

    Venturi Ejector Air Flow Mechanics

    Hi,

    I am trying to figure out the strength of the various type of airflow for my Venturi ejector device. Please refer to my diagram that illustrates scenario A or scenario B. The SAME amount of compressed air is injected for both scenario A and B. For simplicity, I have added to an electrical generator to measure the strength or power of the airflow.

    1. I would like to know which scenario (A or B) would generate more power with the generator.

    2. And by what factor would the difference in power level of the airflows between A and B?

    I am trying determine if the power of sucked air flow is better or worse than the power of direct air flow. If any engineers can help me out with the calculations, I would greatly appreciate it.

    Thanks in advance!
    Attached Images Attached Images

  2. #2
    Principle Engineer Cragyon's Avatar
    Join Date
    Feb 2013
    Location
    Newark, NJ
    Posts
    248
    "A", as "B" air flow would be that produced by vacuum created by the flow perpendicular to it.

  3. #3
    Associate Engineer
    Join Date
    Dec 2019
    Posts
    6
    Quote Originally Posted by Cragyon View Post
    "A", as "B" air flow would be that produced by vacuum created by the flow perpendicular to it.
    Thanks for your reply. Are you saying the power of the airflow spinning the turbine in A, would be greater B? And therefore the electrical output of the generator (Kwh) in A displays a higher power output? For example, if the display output in A is 100 Kwh, what would the output in B typically be?

    I also think power output of A greater than B is most likely the obvious answer. But, in my case, I am trying to work out how we might obtain the power output in B, such that it can equal A. Since the energy of the compressed air injected in A and B is exactly the same. So in theory, the energy that can be converted to airflow power in both cases should be the same. If not, where has the energy loss occured?
    Last edited by mellotango; 04-06-2020 at 07:49 PM.

  4. #4
    Technical Fellow jboggs's Avatar
    Join Date
    Mar 2011
    Location
    Myrtle Beach, SC
    Posts
    841
    You're getting into an area where details and specific terminology matter. For example you mention "strength", "power", "energy". These terms all have very specific meanings, and are not the same thing. Also, the shape, size, and arrangement of your fan blades would make a huge difference. I would recommend you do some research with companies that are known for their venturi products such as Exair, Vortec, Nexflow, or many others. They have done the research and published results. Its one thing to try to maximize air volume flow. Its another to try to maximize air velocity. The surrounding environment also affects results. Bottom line - I don't think there is one simple answer to your question.

  5. #5
    Principle Engineer Cragyon's Avatar
    Join Date
    Feb 2013
    Location
    Newark, NJ
    Posts
    248

  6. #6
    Associate Engineer
    Join Date
    Dec 2019
    Posts
    6
    Quote Originally Posted by jboggs View Post
    You're getting into an area where details and specific terminology matter. For example you mention "strength", "power", "energy". These terms all have very specific meanings, and are not the same thing. Also, the shape, size, and arrangement of your fan blades would make a huge difference. I would recommend you do some research with companies that are known for their venturi products such as Exair, Vortec, Nexflow, or many others. They have done the research and published results. Its one thing to try to maximize air volume flow. Its another to try to maximize air velocity. The surrounding environment also affects results. Bottom line - I don't think there is one simple answer to your question.
    To be honest, I am not a qualified engineer but I am interested to conceptualize a energy recovery system for high pressure waste flue gas. And using a simple gas turbine technology. Diagram A would be common gas turbine systems in use where the combusted gas is directly forced onto the turbine impellers, which in turn generates electrical power. In my case, I do not want polluted flue gas to directly contact the impellers as this would greatly shorten its lifespan. Hence, I want to reposition the turbine at the said position in diagram B, and use venturi method to instead, suck in clean air, to drive the turbine. But my broad question is, is there anyway I can output the same amount of electrical power I would have normally obtained from A? By laws of physics, I see that energy is always conserved but can be changed from one form to another. i.e. same amount of injected compressed air/flue gas for A and B. So there is no reason why we cannot generate the same amount of power from scenario B, unless there is undetected energy loss somewhere, and we can think of a way to recover that back.

  7. #7
    Technical Fellow jboggs's Avatar
    Join Date
    Mar 2011
    Location
    Myrtle Beach, SC
    Posts
    841
    "energy is always conserved but can be changed from one form to another"
    Yes but... That transition always includes losses in the form of waste heat. So, its never 100%. That's where the term efficiency comes in.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •