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  1. #1
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    Purging Capillary Tube with Nitrogen



    Hye,
    I am not sure if this is the right place to ask this question, but I hope someone in the forum may answer this question.

    I've posted a thread few weeks back regarding copper capillary tube. You see, I am actually writing a research project about capillary tube and its manufacturing.

    Now I am stuck at the purging process with Nitrogen. Because of the small diameter of capillary tube and its quite thick wall thickness (often cap tube with dimension 1.9mm O.D x 0.6mm Wall thickness), and with 100 kilogram per coil, it will take 18000 MINUTESS!! to purge the inside of the cap tube with Nitrogen so to prevent oxidation from happening before being brought into the annealing furnace. I know in order for me to reduce the time of this, I can REDUCE the coil weight (so less length), and increase the Nitrogen pressure at the inlet. all of these is to reduce the manufacturing cost.

    But I also notice, when I change the dimension of the tube, either the diameter, wall thickness or both, the purging time will also change. Now comes my dumb question. What should I look into, in terms of tube dimension, to see the trend of the increase / decrease in purging time?? I mean is there any ratio that I should look into to see the trend like for example the higher the ratio between the volume and wall thickness, the longer purging time needed? Something like that??

    Is there any formula to present the pressure gas drop inside the cap tube?

    Is there any way to purge Nitrogen inside the tube with less time?
    Thanks!



  2. #2
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    Re: Purging Capillary Tube with Nitrogen

    Any chance of displacing the oxygen earlier in the manufacturing process?
    Before it is an actual capillary tube...



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  3. #3
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    Re: Purging Capillary Tube with Nitrogen

    Quote Originally Posted by The Viking View Post
    Any chance of displacing the oxygen earlier in the manufacturing process?
    Before it is an actual capillary tube...



    .
    The process flow will be this way:

    Tube drawing (from 30mm to 1.9mm) -> coiling / level wound coil -> "intermediate storage" of about 1 day -> purging with Nitrogen outside furnace -> heat treatment inside furnace..

    I was thinking the tube could be purged during the "intermediate storage" / reduce the coil weight to the optimum size / increasing the pressure of the Nitrogen gas during purging..

    But first of all, I need the equation to represent the pressure drop in a cap tube, which can show me the effect of the dimensions (wall thickness and diameter) to the purging time / pressure drop..

    Another question, usually, what is the maximal carbon residue from lubricant allowed to be in the cap tube before it can be used as expansion valve in refrigerator?

  4. #4
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    Re: Purging Capillary Tube with Nitrogen

    So,
    If you could find a way to purge the 30mm pipe and prevent oxygen to reenter during the drawing process you are on to a winner?



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  5. #5
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    Brian_UK is online now Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
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    Re: Purging Capillary Tube with Nitrogen

    There are lots of experiments and equations on the net regarding capillary pressure drops so perhaps a search on there would provide some more precise answers.

    Is your 30mm pipe drawn through a sized orifice type die? if so, can you pre-charge the 30mm with N2, plug the end and raw it down?

    Or, hold the coil in a good vacuum chamber prior to sealing the ends.
    Brian - Newton Abbot, Devon, UK
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