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Calculating force input to air cylinder by airflow rate

  1. Mar 17, 2016 #1
    Hello there

    I'm having real difficulty with a problem to do with air cylinders and would really appreciate some help. I'm attempting to replicate the human breathing system in a simplistic form but I'm having trouble calculating the force required to provide the correct airflow rate at the mouth. My system will be some form of air cylinder or bellows driven by a linear actuator/servo motor. The trachea, larynx, pharynx, etc will be replicated using standardised garden hose (very basic but the diameters are very similar).

    I have an air cylinder of diameter, D1, where the piston is driven by an external force, Fd. This cylinder is of a known volume (approximately 5 litres), therefore, I know what the stroke length of the piston will be. D1 will then suddenly contract to a smaller diameter, D2 (20 mm) and continue as this diameter until the exit of the mouth 375 mm from the lungs. The airflow at the outlet of the hose/mouth will be 400 litres/min at it's peak, although the flow pattern is a sine wave and the average is lower. The pressure in the cylinder is unknown.

    My question is: how can I calculate the force, Fd, required to provide the 400 litres/min airflow at the output of the hose/mouth?

    Thanks in advance and sorry if the question is scrappy

  2. jcsd
  3. Mar 17, 2016 #2


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  4. Mar 17, 2016 #3
    Hi Nidum,

    Thanks for the link. That system is a lot more sophisticated than the one I am after but I think it's along the right tracks of what I need so thank you again! Might be a life-saver there.

    And in response to (2): my mistake. That was the wrong term to use. I meant the breathing pattern, not the flow pattern.

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