Selecting Copper Tube

Discussion in 'General Electronics Chat' started by Bronchos, Nov 14, 2013.

  1. Bronchos

    Thread Starter New Member

    Sep 8, 2013
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    Hi there

    I have a question. What are the considerations on selecting copper tube for conductor??

    I need copper tube for induction heating coil. It will transfer 30 kVA (the current about 3000 A) and will be cooled by water. The frequency is 10kHz - 40 kHz. I tried to select the copper tube by considering only the ampacity and I got a 2.5 " pipe. It looks weird (because a don't know the basic), haha

    So, anyone can help me?

    Thanks guys
     
    Last edited: Nov 15, 2013
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Since it is going to be water cooled it can be much smaller. Before I bought pipe I would worry about how I was going to switch it.:eek:
     
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  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,010
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    In your application you should consider size, make it large enough to flow the amount of water needed to keep it cool enough not to melt. And I'd use refrigeration tube not the every day water line tubing. Refrigeration tubing is a stronger thicker wall than standard tubing.

    Here's a link to a PDF of more than you would ever need to know about copper tubing.:)
    http://www.chem.mtu.edu/~fmorriso/cm3215/copper_tube_handbook.pdf
     
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  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You need annealed and the best way to join it is with silver solder for H.F. coils.
    Max.
     
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  5. wayneh

    Expert

    Sep 9, 2010
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    The cross sectional area of the copper is a key factor. You can tolerate a much higher ampacity per square cm of copper because you have water cooling. I'd try to estimate the cooling rate per cm^2 of internal surface area, and compare that to the rate of heat generation in a corresponding segment of tube due to the amps passing through it.

    It's a lot of geometry and keeping track of units, but you should be able to work out a value on paper. Draw a picture - I couldn't do it without one.
     
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  6. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    You could probably get by with 3/4" tubing with sufficient cooling.
     
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  7. wayneh

    Expert

    Sep 9, 2010
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    Similar to the most common last words in Wisconsin - "Hold my beer and watch this!"

    Look, the cooling system can reject some number of joules, probably limited by a heat sink or fan or some other weakest link. All of that heat must move through the face of the copper surface area touching the coolant. The surface area for heat exchange is easily calculated as a function of tubing length and diameter.

    The heat generated can also be easily calculated from the amperage, cross section of copper, and length of tubing. These heat values have to match up, or the copper will make more heat than the water can take away.

    I would not design the system so that the tubing is the weakest link, since it may corrode or lime over with time and you need to allow for a good safety margin.
     
  8. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
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    The smallest induction heater we had at the steel mill was 5mW each X6.
    The coils were water cooled square section, about 3" on a side.
    We also had 6-10mW and 6-20mW heaters all of very similar design to the 5mW jobbies.

    When one of the 5# thermocouples fell between a coil creating a huge, but quick short, it was pretty spectacular.
     
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  9. Bronchos

    Thread Starter New Member

    Sep 8, 2013
    13
    0
    Oh yes, thank you all for the respons.

    So, what temperature the cooler must keep so the copper tube is safe enough? And, how to calculate the ampacity rise after the copper tube is cooled?
    My friend in the project will try to determine the cooler requirement.

    Thanks again....
     
  10. colinb

    Active Member

    Jun 15, 2011
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    Do you mean megawatt or milliwatt?
     
  11. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    I'm sorry, I should have seen that. They were all megawatts, 210 in total.

    Three of them (5,10,20) would take a 5' x 20' x 1' slab of steel from ambient to ~3,000F in 20 minutes. They looked like upside down toasters. With 5 more groups like that, they kept the rolling mill on its toes.
     
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