Ideal gas pressure curve VS Adiabatic pressure curve

[sonargod]

I am working on a personal project that simulates an airgun on Microsoft Excel. I basically measure velocity every eighth of an inch given the original volume of my valve and the inner diameter of my barrel. The problem I have is that I am not sure how to do a Adiabatic Pressure curve. I understand how it works, but I am not sure how to what math to use. I appreciate any assistance you can give me. I have a fairly basic background in physics, but I have never worked with this sort of thing up until now, and it is something that I would like to learn. I am using compressed air in all my calculations. Thanks for the help, and I look forward to your response.

 

[Montemayor]

Son:

Unless you are a professional engineer, I prefer not to discuss the application of a thermodynamic process that could cause you or some one else harm. Much more than a basic knowledge of physics is needed to engineer and design what you are describing.

You may feel very qualified and enthusiatic about science and engineering as well as its applications. But to do an application safely and correctly you need the basic training in math and engineering - not just the willingness and enthusiasm. I highly recommend you steer your interest in the direction of thermodynamics through a regular Mechanical or Chemical Engineering degree. That would give you a definite jump on materializing a lot of your inventiveness.

 

[iainuts]

Hi sonar. Personally, I'll have to disagree with M. I see nothing wrong with creating a spread sheet to simulate an airgun, nor even making one. It's generally not considered illegal, and in fact, you could pick up a much more deadly weapon at your local Walmart.

Note that an adiabatic process is one in which no heat is lost or gained by the fluid undergoing the process. It says nothing about work being done on or by the gas. Any time a gas is expanding against something such as a piston, it is undergoing an polytropic process. Google "polytropic process".

Basically, the equation you want is PV^n = constant. The exponent for air with no heat transfer is the ratio of specific heats (k = 1.4). Note also this is absolute pressure, not gage pressure.

 

[sonargod]

Thanks for the help you guys. I am currently in the Navy as a sonar technician, and although I have a good background in acoustics and oceanography, I do not have my mechanical engineering degree. I am taking online classes for my required credits, but I have not been able to take sufficient math and science online for the kind of stuff I am interested in. Any suggestions on that would be helpful. I have studied the Navy's Hydraulics and Pnuematics courses, but they are pretty basic when it comes to some of the stuff that I am trying to do and simulate. I do this kind of stuff out to sea so that I can learn more. I figure that when the time comes to take my college classes, it will be a whole lot easier if I already have a little experience.

 

[iainuts]

Hi again, sonar. You sound like what I did 20 years ago. I was an aircraft mechanic in the USAF at Pope AFB. I spent 4 years enlisted, but during that time I took a lot of evening courses that would transfer to college. After that I spent 4 years to get a BSME.

I think the thing that helped me most in college was the chance to focus on the engineering courses. I didn't have to take any humanities courses or other non-engineering courses during college as I had already taken those while in the service during the evening. They all transferred. Very few other courses were accepted because the college I went to was very particular about what math and science courses could transfer but very lenient about which humanities courses transferred. End result was I could generally get out of taking Enlish, humanities and other courses and focus on engineering. That helped increase the amount of time I had to study engineering during college which was a terrific help in all sorts of ways. So I'd suggest looking at getting the boring courses out of the way while you're still enlisted. That will give you more time for the fun stuff when you go to college.

Also, this forum is primarily for practicing engineers. You might prefer chatting with other students, such as at PhysicsForums:

http://www.physicsforums.com/

It's a good message board for people like yourself that are still in college.

Good luck in the service.

 

[AminG]

Hello Sonargod,

I think you may be simulating the ballistics equation and I will dig this up from my notes as I know I cannot quote the equation from memory.

During my school days, we did exactly what you are doing and I wrote a code which simulates pressures, temperature of the gas including shock waves and expansion waves.

I will be happy to share this with you - drop me an email (aming@adelphia.net)