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  1. Peter C

    Full tank being emptied - Bernoulli

    @snickster, thank you. But solve your second equation... you have a p.g.h = 1atm - 0.5 psi this can only be true if h is big enough to almost reach atm pressure (about 10m). If my tank is a 5m tank, this can never be true... but in no moment we have add values so far, so how can the equations...
  2. Peter C

    Full tank being emptied - Bernoulli

    @snickster, when you say that in scenario 2/ one would have a pressure difference generating flow (1atm + p.g.h - 1atm = pressure difference generating flow). In that case, if we just see the equation, ALL liquid would come out, not mattering the height of the tank... that's something I can't...
  3. Peter C

    Full tank being emptied - Bernoulli

    So just to confirm: if I put a manometer on the topside (Mt) and at the bottom (Mb). 1/ Once all the valves are closed: Mt = 1bara Mb = 1 + p*g*h bara 2/ Once the bottom valve is opened Mt = 1 - p*g*h' (h' measured from the bottom to the top) Mb = 1bara where bara is the absolute pressure...
  4. Peter C

    Full tank being emptied - Bernoulli

    But what if the tank is 5m high?
  5. Peter C

    Full tank being emptied - Bernoulli

    @all thank you for your valuable comments. I'm indeed aware of the bottle experiment. Bit I'm trying to model the problem first. Besides, a pin hole won't let any flow indeed once the bottle is closed, but a big hole will... @Snickster, thank you for that detailed answer. Indeed that was what I...
  6. Peter C

    Full tank being emptied - Bernoulli

    So indeed there are two different force balances: 1/ when the valve is closed: at that point the pressure at any given point is 1atm + p*g*h from h mesured from the top to the bottom ; 2/ once the valve is opened, there is an equalization at the bottom pressure and the external pressure (because...
  7. Peter C

    Full tank being emptied - Bernoulli

    I agree that no water would come out if level is under 32ft, yet I can't explain using just static equations. For me, pressure at the bottom of the tank will not be lower than the ATM pressure. In fact, pressure at the bottom will be 1atm + column height. As a reminder, tank was filled with a...
  8. Peter C

    Full tank being emptied - Bernoulli

    Hello, Very commonly people we hear that a tank where column pressure is not big enough to overcome Patm will not empty by itself. In my opinion, most of those who say that forget that once the tank was open to be fulled and, therefore, we must add 1atm pressure to the fluid at any point. So...
  9. Peter C

    Pipeline emptying + liquid flashing at subatmospheric pressure

    So considering that the values given in the image are in meters, what would be the final configuration in pipe? I am having troubles to model the siphon phenomena and, therefore, the flashing one. Besides, is Bernoulli applicable in that situation given that it's a transitory state and not...
  10. Peter C

    Pipeline emptying + liquid flashing at subatmospheric pressure

    Fellow 1503-44, I agree with all your points. They will be very helpful. However I have a question and a point that i disagree : 1) Calculating velocity would be the only way to check if siphon will occur or not? There is no way i could trae a line saying: above that height there will be...
  11. Peter C

    Pipeline emptying + liquid flashing at subatmospheric pressure

    That's a very interesting point, but I don't always agree that line won't drain: if the drain diameter is big enough so air can "overcome" surface tension (that would be a second part of that problem...) then a slug flow may happen. Of course it's not optimum since flow will not be constant... I...
  12. Peter C

    Pipeline emptying + liquid flashing at subatmospheric pressure

    Hello guys, thank you for all your comments. I am taking the time now to read all of them. Just to clarify, the line profile showed is just for example, the height values (y axe) should be ignored. I am not trying to solve a specific example, but more general one. In fact, I want to understand...
  13. Peter C

    Pipeline emptying + liquid flashing at subatmospheric pressure

    Hey thank you for your reply! I still have a lot of questions, given that in the example, our fellow colleague had some inlet air valves, while in my case the pipe is fully closed. Please, let's consider the case bellow: Suppose I open the drain located at x = 6. 1) At first, pipe would...
  14. Peter C

    Pipeline emptying + liquid flashing at subatmospheric pressure

    It seems easy, yet it’s quite complicated. Considering a full pipeline (e.g., water) close on both ends and without any venting valve. A drain is opened at a location of the pipe allowing fluid to flow out just by gravity. It is clear that all product in the vicinity and in a higher level than...
  15. Peter C

    Pneumatic pump

    Dear all, thank you for your reply. I am sorry for the lack of precision, but I meant to do a more general question: if a pneumatic pump can increase a pressure vessel pressure to a value grater than the compressed air pressure. I feel like at some point the fluid pressure will reach the air...
  16. Peter C

    Pneumatic pump

    Hello ! If I have a pneumatic pump connected to a fluid tank (fluid source), compressed air source (pressure source) and a closed tank full of liquid (output), can I increase my tank (output) pressure up to a value higher than my compressed air pressure? Thank you in advance :)

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