Pressure rate increase between two vessels

  • Thread starter Thread starter j117
  • Start date Start date
  • Tags Tags
    Pressure
AI Thread Summary
The discussion centers on the challenge of achieving a specific pressure increase in two cylindrical vessels using air, with a target of 0.525 mbar in vessel two within 0.3 seconds. The initial calculations suggest that the pressure dynamics may not hold due to the doubling of volume when the valve opens. Safety concerns are raised about using compressible gases for structural testing, with recommendations to use water instead. The importance of understanding gas behavior during rapid pressure changes is highlighted, suggesting that computational fluid dynamics (CFD) may be necessary for accurate modeling. The thread ultimately faces closure due to safety concerns regarding the testing methods discussed.
j117
Messages
2
Reaction score
0
TL;DR Summary
generating pressure between vessels to check for structural integrity
I have to cylindrical vessels using air as a medium. I want to pressurise vessel one, release the pressure into vessel to and register a .525mbar pressure in vessel 2 - within .3s.

My understanding so far,
dp/dt = 175000 Pa/s required

P1V1/n1 = p2v2/n2
52500 * 0.088627484 * 0.0041846 = 52500 * 0.088627484 * 0.0041846

for me if I have the required pressure in the same volume, and release this within 0.3 seconds, then i will get the exact same pressure on the opposite side.
But, once the valve is opened, the volume essentially doubles.

would I double the volume on V2 but i don't want the final pressure in V2 to change

My aim is to generate the pressure on the bottom section and see if it remains structurally sound.

any help please?
 
Engineering news on Phys.org
Welcome, @j117 !

For structural test of recipients, use water and a pump rather than compressed air.
It is not safe to use any compressible gas.
 
  • Like
Likes russ_watters and berkeman
the test has to be air, it is to replicate a delayed ignition in gas appliances, all safety is taken care of. I used a small tube to fill, the rate was not fast enough as I need am immediate impact as would be experienced in real terms
 
I don't see how the equations you posted are relevant.
I believe you're trying to apply the ideal gas equations.

Initially, everything is known
1696182239469.png


After the expansion, we can find the equilibrium state assuming some things
1696182258314.png


The final volume I assume is known.
Then, if no mass is lost ##m=constant## and the process is adiabatic ##Q=0## we can conclude the internal energy will be the same as in the beginning because there is no work coming out ##W=0##.
$$\Delta U = Q-W \rightarrow U_f-U_i=0 \rightarrow U_i = U_f$$
Since the internal energy is only a function of the temperature in ideal gases, then the temperature must be the same before and after the expansion.
$$U_i = U_f \rightarrow T_i=T_f$$
You can check this link for more information about that.
https://en.wikipedia.org/wiki/Joule_expansion

Anyway, if you want to know something like ##dp/dt## you will need to characterize so many things that I believe it's easier to just use CFD. The gas will accelerate through the valve and then collide with the chamber walls. Something similar to a water hammer. I'm not certain if the pressure on the walls could be at some instant higher than the equilibrium pressure it will end up reaching as time goes on because of the mentioned collision.

Maybe if you check more info about water hammers and their gaseous version you can find something that works for you. If that's the case, post it back. It'd be interesting to read.
 
Thread is in Moderation...
 
Lnewqban said:
Welcome, @j117 !

For structural test of recipients, use water and a pump rather than compressed air.
It is not safe to use any compressible gas.
j117 said:
the test has to be air, it is to replicate a delayed ignition in gas appliances, all safety is taken care of. I used a small tube to fill, the rate was not fast enough as I need am immediate impact as would be experienced in real terms
After Mentor review, this thread will remain closed per the "dangerous discussion" prohibition in the PF rules.

From the Mentor discussion about this thread:
Delayed ignition is a lot like a potato gun without the potato in that the temperatures and pressures are very similar. Peak pressure on the order of 35-40 PSI is a number that sticks in my mind, and is consistent with what I observed when I watched a friend firing tennis balls from a potato gun.

The larger concern is that a test with compressed air does not properly test the system. If I was running this testing, I would set it up for the worst delayed ignition possible, then program it to repeat until stopped. My passing criteria would be about 100,000 cycles with no catastrophic failures. Allowable failures, such as the flame sensor, would shut the system down.
 
  • Like
Likes Lnewqban
Posted June 2024 - 15 years after starting this class. I have learned a whole lot. To get to the short course on making your stock car, late model, hobby stock E-mod handle, look at the index below. Read all posts on Roll Center, Jacking effect and Why does car drive straight to the wall when I gas it? Also read You really have two race cars. This will cover 90% of problems you have. Simply put, the car pushes going in and is loose coming out. You do not have enuff downforce on the right...
I'm trying to decide what size and type of galvanized steel I need for 2 cantilever extensions. The cantilever is 5 ft. The space between the two cantilever arms is a 17 ft Gap the center 7 ft of the 17 ft Gap we'll need to Bear approximately 17,000 lb spread evenly from the front of the cantilever to the back of the cantilever over 5 ft. I will put support beams across these cantilever arms to support the load evenly
Thread 'What's the most likely cause for this carbon seal crack?'
We have a molded carbon graphite seal that is used in an inline axial piston, variable displacement hydraulic pump. One of our customers reported that, when using the “A” parts in the past, they only needed to replace them due to normal wear. However, after switching to our parts, the replacement cycle seems to be much shorter due to “broken” or “cracked” failures. This issue was identified after hydraulic fluid leakage was observed. According to their records, the same problem has occurred...

Similar threads

Back
Top