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Thread: Pulleys and V-Belts

  1. #41
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    Quote Originally Posted by WAYNE3298 View Post
    I try to help chops but sometimes underestimate the reactions. The post with the container that had the rising air bubble excited a lot here. That one understandably is impossible for a lot of people to wrap their head around and I'm not poking fun at anyone.
    Whoa.... rising air bubble?

    Interesting..... What was that all about? More more...... I'm bored.

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  3. #42
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    A tank is filled with water and the tank is pressurized to the point that the rupture disk on it is pressurized to the maximum it can handle. There is an air bubble near the bottom of the tank that starts rising when it does will the rupture disk burst?
    No man can be both ignorant and free.
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  4. #43
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    Pulleys and V-Belts

    Quote Originally Posted by WAYNE3298 View Post
    A tank is filled with water and the tank is pressurized to the point that the rupture disk on it is pressurized to the maximum it can handle. There is an air bubble near the bottom of the tank that starts rising when it does will the rupture disk burst?
    I dont think it will because were dealing with a closed system. Assuming the temperature and pressure stays constant the tank is a closed system. No additional energy or pressure is being added by the bubble because its inside of a closed system that is already at equilibrium.

    I guess Im going off of the principle in physics that you cant get something from nothing. You would have to add an air bubble from outside the system to change the equilibrium and increase the pressure.
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  5. #44
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    Quote Originally Posted by WAYNE3298 View Post
    A tank is filled with water and the tank is pressurized to the point that the rupture disk on it is pressurized to the maximum it can handle. There is an air bubble near the bottom of the tank that starts rising when it does will the rupture disk burst?
    Yes and no.

    That air bubble would not exist to begin with. It would either be at the top of the tank already, or absorbed into solution.

    Either way at point of pressure release, the air would be the first to escape.


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  6. #45
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    I remember that thread, but can't remember the answer. Here's what I probably said, which was probably wrong, LOL . . .

    Yes, the rupture disk will burst. Because the bubble no longer has the weight of the water above compressing the bubble. So, when it rises, it expands, and there goes the rupture disk.


    Quote Originally Posted by WAYNE3298 View Post
    A tank is filled with water and the tank is pressurized to the point that the rupture disk on it is pressurized to the maximum it can handle. There is an air bubble near the bottom of the tank that starts rising when it does will the rupture disk burst?
    I do a triple evac with nitro to remove non condensables.

  7. #46
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    Quote Originally Posted by WAYNE3298 View Post
    A tank is filled with water and the tank is pressurized to the point that the rupture disk on it is pressurized to the maximum it can handle. There is an air bubble near the bottom of the tank that starts rising when it does will the rupture disk burst?
    That sounds like an interesting thread, are we starting this here?

    These are my thoughts on it...

    For simplicity lets say the tank is 120 feet tall. And using rough numbers that would place about 50 Lbs of liquid column weight at the bottom. The tank is filled with water everywhere except for this single bubble at the bottom of the tank.

    If there was a bubble at the bottom it would be compressed with that 50 psi of water. We know that every force has an equal and opposite reaction, so we can also say the bubble is pushing back with 50 psi when its at the bottom.

    As the bubble rises up, that weight is going to become less so the bubble is going to push back against the water. In an open atmosphere this would normally result in the bubble expanding, but in a pressure vessel there is no room for expansion, and since water is not compressible the bubble stays the same size all the way to the top and continues to exert against the water at the top with the same amount of force that it did at the bottom.

    The pressure in the tank will be the same at the top as it is at the bottom because that bubble is applying the same amount of force at the top of the tank that it was at the bottom.

    The rupture disk will not rupture because the pressure has not changed.
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  8. #47
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    I think that's the answer, but I can't wrap my head around it. Even though the vessel is closed and pressurized, how can the water have no 'weight' ?


    Quote Originally Posted by thatguy View Post
    That sounds like an interesting thread, are we starting this here?

    These are my thoughts on it...

    For simplicity let’s say the tank is 120 feet tall. And using rough numbers that would place about 50 Lbs of liquid column weight at the bottom. The tank is filled with water everywhere except for this single bubble at the bottom of the tank.

    If there was a bubble at the bottom it would be compressed with that 50 psi of water. We know that every force has an equal and opposite reaction, so we can also say the bubble is pushing back with 50 psi when it’s at the bottom.

    As the bubble rises up, that weight is going to become less so the bubble is going to push back against the water. In an open atmosphere this would normally result in the bubble expanding, but in a pressure vessel there is no room for expansion, and since water is not compressible the bubble stays the same size all the way to the top and continues to exert against the water at the top with the same amount of force that it did at the bottom.

    The pressure in the tank will be the same at the top as it is at the bottom because that bubble is applying the same amount of force at the top of the tank that it was at the bottom.

    The rupture disk will not rupture because the pressure has not changed.
    I do a triple evac with nitro to remove non condensables.

  9. #48
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    You guys are coming up with some good thoughts and some good ways to explain your thoughts.
    No man can be both ignorant and free.
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  10. #49
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    since this threads has gone completely off the rails, regarding the air-bubble problem...

    at first glance, the rupture disk will not break due to no other outside forces have been introduced to increase the pressure (i.e., heat, volume, change in molecular mass, etc.), however, depending on:

    1. the height of the tank
    2. the total mass of the air bubble
    3. viscosity of the water
    4. how close to breaking the rupture disk truly is
    5. assuming the rupture disk is at the top of the tank

    breaking the rupture disk is possible due to the force of momentum of the air bubble as it hits the rupture disk and adds its force to the total pressure already exerted on the disk
    "Right" is not the same as "Wise".

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  11. #50
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    I'm confused..... To me a pulley is something you pull on and a sheave is what you get stuck with by your cell mate (actually probably shiv but easily mistaken).

    The point is that many words, in fact more than realized, have alternative meanings but still we understand. If a tech tells me the pulley is worn out I'm not going to try to correct them as I do understand what they mean. I say pulley when I don't want to sound like a techy or introduce unfamiliar terms.

    All tech talk has it's own language. Sometimes letting on when a tech got their education. When a capacitor is called a condenser. When I'm told the power at a duplex was 110 or 115 or 120 volts shows the evolution of supply power over the years. So if a tech tells me they have 110 at the outlet I'm not going o argue.

    It seems to work backwards in some marriages. The two always think they know what the other said or means when they both operate in Area 51, cluelessness. Anyone read the cartoon Pickles? For younger people that don't know about this it might be because marriages evolve (or devolve) sometimes rather slowly.
    I have no personal knowledge of this phenomenon but it's rumored to occur.
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  12. #51
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    I think......

    If the vessel is sealed, and totally full, with a bubble inside, and the temperature of the vessel and it's contents stayed the same, the pressure on the non-compressible liquid is the same as the pressure on the compressible bubble. The rupture disc shouldn't care if the bubble is moved because all of the contents of the vessel pressure are in a steady state, and any extra energy as a result of induced movement should be absorbed by the compressible bubble....

  13. #52
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    So, what you are saying is that the water has no weight. Pressurized vessel or not, if the water is at sea level, it has weight.

    Maybe what I am missing is where the pressure is taken from. If, as mentioned prior, you have a 120' column of water in a pressurized container, how can the pressure be the same at the top as it is at the bottom?


    Quote Originally Posted by Artrose View Post
    I think......

    If the vessel is sealed, and totally full, with a bubble inside, and the temperature of the vessel and it's contents stayed the same, the pressure on the non-compressible liquid is the same as the pressure on the compressible bubble. The rupture disc shouldn't care if the bubble is moved because all of the contents of the vessel pressure are in a steady state, and any extra energy as a result of induced movement should be absorbed by the compressible bubble....
    I do a triple evac with nitro to remove non condensables.

  14. #53
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    Quote Originally Posted by BBeerme View Post
    So, what you are saying is that the water has no weight. Pressurized vessel or not, if the water is at sea level, it has weight.

    Maybe what I am missing is where the pressure is taken from. If, as mentioned prior, you have a 120' column of water in a pressurized container, how can the pressure be the same at the top as it is at the bottom?
    Still thinking.....doesn't hurt yet....

    In the presence of gravity, to force the bubble to move from it's steady state position, you would need to add extra energy to the vessel to force the bubble to move. The movement could be a result of rotating the vessel. The compressibility of the bubble would save the rupture disc.

    The way I'm trying to understand this is that it's a displacement discussion. In the presence of gravity, the bubble would naturally be found at the top of the steady state vessel, in an area of least resistance for it.

    In order to make it move you would need to add the additional energy which would be absorbed and then be released by the compressible bubble.

  15. #54
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    Your thoughts are on target Artrose but forcing the bubble to move isn't part of the problem even though in a real application as was previously brought out it wouldn't rise on it's own. This problem was thought up by a professor teaching hydraulics for the purpose of getting us to better understand reactions. He was trying to get the point across that an air bubble in water doesn't expand because the pressure inside it increases but that the pressure external to it decreases and that only happens in an atmospheric tank.
    I'm aware you guys think things out but you exceeded my expectations on this one.
    No man can be both ignorant and free.
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