How to calculate pressure frmo force on piston

[twmc]

Hi. I'm new here so apologies if this isn't posted in the correct place.

I'm facing a problem. The situation is this: At a tunnel portal, I am harvesting the energy of the piston effect from trains entering and exiting. I have a number of sails located around the portal edge that. Each sail spans between two lightweight arms that, when hit with the passing air, are forced to rotate around a pivot.
Attached to these arms is a piston. As the arms are forced to rotate outward from the passing air, the piston is exhausted and the air injected into a pneumatic muscle.

I want to work out the rate of pressure increase for the muscle (I have a test rig to determine to rate of contraction from a certain pressure). The average power of each pulse (10s) of the piston effect is 89W. How do I find out the pressure of the system?

My current approach is this:
Let's take one sail as receiving all the power from the piston effect. The sail is pivoted at the top end, with the force hitting the bottom, is 2m long and in a vertical position. The piston is attached 1m from the pivot. Therefore the moment per second will be 89x2=178Nm. As the piston is attached 1m from the pivot, the moment transferred will be 89Nm.

Am I right in thinking I have to calculate the volume of the system (volume of hose = volume of air muscle) then consider the volume or air injected by the piston in order to calculate a pressure increase for each pulse?

I hope someone can help.

Thanks.

 

[Achy47]

Thank you for your post and welcome to the forum! It sounds like you have an interesting project going on with harvesting energy from the piston effect of trains. In order to determine the pressure increase in your system, you are correct in thinking that you will need to calculate the volume of air injected by the piston and compare it to the volume of your air muscle.

To calculate the volume of air injected by the piston, you will need to know the displacement of the piston and the frequency of the pulses. The displacement can be measured by recording the movement of the piston over a certain period of time, and the frequency can be determined by counting the number of pulses per second. Once you have these values, you can use the formula V = A x d x f, where V is the volume, A is the area of the piston, d is the displacement, and f is the frequency.

Once you have the volume of air injected by the piston, you can then compare it to the volume of your air muscle to determine the pressure increase. This can be done by using the ideal gas law, PV = nRT, where P is the pressure, V is the volume, n is the number of moles of gas, R is the gas constant, and T is the temperature. Since you will be using air as the gas in your system, you can assume that the number of moles and the gas constant will remain constant, and therefore the equation can be simplified to P1V1 = P2V2, where P1 is the initial pressure and V1 is the volume of the air injected by the piston, and P2 is the final pressure and V2 is the volume of your air muscle. Solving for P2 will give you the pressure increase in your system.

I hope this helps and please let me know if you have any further questions. Good luck with your project!