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Theoretic Blower Problem

  1. Jan 12, 2012 #1
    Settle an office debate:

    If we have two identical blowers and connected the inlet of Blower A up to the outlet of Blower B and then connected the inlet of Blower B up to the outlet of Blower A, what would happen to the flow rate at the outlet of either one when each one is energized simultaneously.

    Keep in mind the spirit of the question here: this is totally theoretical, and all possible differences between the blowers and their power supplies, etc. are eliminated.

  2. jcsd
  3. Jan 13, 2012 #2


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    Isn't this the same as having a blower with its inlet connected to its outlet? The length of pipe between the blowers becomes a factor here. Consider for example a very long section of pipe. Once they turn on, the pressure immediately upstream will drop and a pressure wave will propogate back to the outlet of the other machine. Similarly, pressure at the outlet of the blower will increase and that pressure propogates forward to the inlet of the opposite machine. Flow rate is restricted by friction with the walls of the pipe so as velocity increases, the irreversible pressure drop along the wall of the pipe increases.

    For very short sections or for the case where we essentially neglect flow restriction, the air velocity increases until the blower can no longer impart any momentum to it, but the pressure right at start up will do the same as for a longer pipe, just much faster.
  4. Jan 16, 2012 #3
    If the two blowers were identical, then that would not be an efficient design. That is why every stage in a gas turbine compressor is different. Each stage is designed to recieve the gas in a certain state from the stage ahead of it, and to deliver it to the next stage with slightly more energy imparted into it.
  5. Jan 22, 2012 #4
    Hi everyone!

    I have a simple question. I have got a centrifugal blower installed at a mill. My problem is that the air generated by it is too much than required by me. I want to lower the air generated & air pressure at outlet of centrifugal blower.

    I know other methods like rpm control, blade sizing, impeller sizing. I have encountered a simple way, just need to verify the outcomes. My blower outlet size is 10" x 18". I just put up a solid box at its outlet so the discharge cross section becomes 10" x 10". Will this help me.

    Quick suggestions needed.
  6. Jan 23, 2012 #5
    Crude, but that should reduce air flow.

    Look out for possible over heating of the motor as you apply more load to it in this manner.
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