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  1. #1
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    When will a tube explode?



    Suppose, filterdryer with a sight glass and a shut off valve at inlet and outlet. We trap 100% liquid R134a in the dryer at 20C.
    How high must we heat this dryer before the tube will burst if the burst pressure is 60 bar?


    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  2. #2
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    Re: When will a tube explode?

    .

    As long as it's not a trick question

    If it's a pure temperature - pressure relationship
    then I work it out to be

    R134a at 60b = 123.5 degsC.

    regards

    Rob

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  3. #3
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    Re: When will a tube explode?

    It's not a tricky question, the liquid will try to expand but it can't because it's trapped. I've had an explosion on a sightglass many years ago because temperature rose from +/- 10C to 25C.
    But I want to see a calculation for this, given also the assumption that the copper or dryer will not expand.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  4. #4
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    Re: When will a tube explode?

    .

    I know sub-cooled liquid expands at an exponential rate
    if trapped, I was the person who had to replace over a
    hundred heat exchangers because of that miscalculation.

    The trouble is, it is not a hydrolic pressure increase if there is
    a vapour there, the liquid will expand if warmed up (hydrolic),
    but if there is the smallest amount of vapour then the liquid would
    be saturated and it would expand as a saturated vapour.

    the pipe will burst at the same pressure but the temperature
    acting on the refrigerant will differ.

    You need a table for expansion of fluids.
    Perhaps see.

    http://www.engineeringtoolbox.com/vo...ion-d_315.html

    http://en.wikipedia.org/wiki/Thermal_expansion

    http://www.answers.com/topic/thermal-expansion

    http://physics.info/expansion/

    Regards

    Rob

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  5. #5
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    Re: When will a tube explode?

    So we need:
    Coefficience of thermal expansion = B
    Isothermal compressibility coefficient = k
    Then DT = (k/B) x DP
    DT = (B/k) x 55.3
    Just trying to find the B and the k which at 39 Bar = 239.3 (expansion) and 0.194 (compression).
    These values change dramatically over the process which makes it complex so I'll do it for 39 Bar.
    DT = 0.048
    20.048 degC
    Which looks wrong so maybe I made a mistake. Also the coefficients change dramatically through the process and I might get more into it tomorrow but I'm hoping Peter will set us straight.
    We can assume the vessel will not expand.
    Coefficients came from http://www.peacesoftware.de/einigewerte/r134a_e.html
    and formula from p171757.pdf[PDF] THE HAZARDS OF THERMAL EXPANSION - Abiquim

    In reading further the pdf it states the rate of increase of 6.6 bar/degC which would = 8.37K or 28.37degC BUT that would only be for a temp below 0degC.
    Last edited by Tesla; 16-04-2013 at 12:46 PM. Reason: Last lines added

  6. #6
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    Re: When will a tube explode?

    Ignore this post, it needs an equation to demonstrate.
    Last edited by Rob White; 16-04-2013 at 02:25 PM.
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  7. #7
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    Re: When will a tube explode?

    It'll go bang long before you think it would, if not we would be able to completely fill bottles etc.
    Mostly found in Oxfordshire, UK :)

  8. #8
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    Re: When will a tube explode?

    go on john, surely u could dig out a drier u havent chopped up and fit a gauge and try it in ur garden- no need for calculations- pure simple test= answer and dirty undies!
    that bit can be edited out of ur videos!!! haha

  9. #9
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    Re: When will a tube explode?

    My friend saw how the test pressure made oxygen... the head of performer punched a concrete plate from above and departed in not the known direction...

  10. #10
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    Re: When will a tube explode?

    Simple question,

    for what conditions are systems build?
    Normaly I would say for worth conditions, right? That means if burst pressure is 60 it should not burst before 60 bars. Otherway a lot of running systems become dangerous.
    So Rob's first answer should be right.

  11. #11
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    Re: When will a tube explode?

    Hi DerMimi and welcome to the forum
    I disagree with your answer and Rob's first answer as it is not a liquid and vapour mix it is a liquid 100% which behaves differently. The Question is looking for the formula and answer. So this is tricky as we have not got it yet. Looks to me like may have to use simultaneous or calculus equation to solve and I am very rusty and time constrained.

  12. #12
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    Re: When will a tube explode?

    it all depends on the expansion of the fluid, if purely hydrualic then any expansion over say 5% will cuase the steel to split, if vapour pressent you'll have a gernade!

    the 500psi opperating will be a 2 to 1 or better safety factore so you'd need to exert a force of 1ksi on the cylinder befor it would tear the steel.

    so the question can be posed: How much exansion can a Fd take befor rupturing? brittle metal veryy little would be my reply.

    Using hydrostatic testing one could say exactly how much pressure would be needed to burst it.

    One should be able to find a burst rating some where for a common FD.

  13. #13
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    Re: When will a tube explode?

    217853_3934791139984_839044388_n.jpgI manufacture copper manifolds for Nitrogen and oxygen bottles.
    6mm, 1mm wall tube, holds 250 bar at pressure test, works at 200 bar.
    Last edited by chemi-cool; 19-04-2013 at 09:02 PM.

  14. #14
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    Re: When will a tube explode?

    http://physics.info/expansion/
    found some geeky stuff!!

  15. #15
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    Re: When will a tube explode?

    Interesting one.

    The expansion of the copper pipe should really be taken into account as it represents real life.

    So if the values for R134a and copper are:-
    B-liquid = 0.002 (volumetric expansion per C)
    K-liquid = 0.0031 (isentropic compressibility 1/MPa)
    B-copper = .000051 (volumetric expansion per C)
    Youngs Modulus of copper - 1.2x10E5 or 120000MPa
    Diameter to thickness ratio of the pipe, lets assume 20mm dia and 1mm thick so r = 20
    T = temperature rise in C

    P (bar)=10*T*(B-liquid + B-copper)/(K-liquid + r/E)

    P=10*1*(0.002 - 0.000051)/(0.003 + (20/120000))

    This equates to 6.15 bar increase in pressure per degree C.

    It would only need 10C rise in temperature to burst the pipe, but this assumes pure liquid and a general expansion of the pipe cubically. Any changes in the geometry can alter the values a lot.

    Hope this helps.

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