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DIY vacuum chamber advice

  1. Dec 2, 2018 #1

    len

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    I need to perform an experiment in vacuum and would like advice on cost effective parts or how to do it.

    The chamber needs to be at least the size of a shoebox. Round is fine.

    The vacuum is required to control heat dissipation of an object as much as possible while I measure its temperature electronically. I’ve yet to figure out the best way to measure it given that it’s in a vacuum. I’ll have an Arduino controller running “outside” the vacuum.

    I see various rotary vacuum pumps on amazon for $100 - $500. I’m not sure what to purchase.

    And another thread suggested using a Bell jar. It looks adequate. I need wires to run inside and seal these somehow.

    Has anyone done this successfully and have some advice?

    Ps, do lazer emitters work “inside” a vacuum?

    Thanks,
    Len
     
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  3. Dec 2, 2018 #2

    davenn

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    hi Len

    How good of a vacuum do you need ?
    Vacuum is measured in Tor .... eg. 0.1 Tor, 1 Tor etc

    show some links so that people here can advise you


    laser = Light Amplification by the Stimulated Emission of Radiation :smile:

    of course .... light travels through the vacuum of space quite happily :biggrin:


    Dave
     
  4. Dec 2, 2018 #3

    len

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    Hi Dave.

    I need to control the heat dissipation “as much as possible”. I also need cost effectiveness. I don’t know what pressure that will be. It depends on how much overtime I get at work this month.

    On amazon there are many pumps. I don’t have any particular one in mind so rather than send links to all of them, I’ve asked if anyone has any experience to share.

    I carefully asked if lazer “emitters” work in vacuum. I’m pretty certain most everyone who ventures onto this website knows that light can travel through a vacuum. Electronics have trouble in vacuum and can be damaged. I’d prefer to save myself from that lesson if I can, if someone already knows if they work in a vacuum.
     
  5. Dec 2, 2018 #4

    davenn

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    wellllllll ..... even just one of those you were looking at would be helpful to get an idea of where you were aiming at :wink:


    they would have to be particularly sensitive to low pressure, most general electronics are not

    there are 2 types of laser emitters generally available .... gas tube type .... Helium-Neon ... wouldn't be good in a vacuum,
    the glass encapsulation may crack, but semiconductor lasers which are just glorified LEDs ... Light Emitting Diodes
    and there wouldn't be any issues

    Dave
     
  6. Dec 2, 2018 #5

    len

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    Hi Dave. A lot of electronics will quickly overheat in vacuum because of the lack of air to dissapte their heat.
    I didn’t know about the LED type lasers but I do need something with high wattage so that doesn’t sound like an LED type.

    I’m not adding any links to random amazon pumps. I only referenced it to illustrate price ranges.

    I’m really searching for someone who’s done this before to steer me In the right direction. But thanks anyway.
     
  7. Dec 2, 2018 #6

    tech99

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    I have used a bell jar in school experiments. The base is usually sealed on to a glass plate using vacuum grease or Plasticine. (Another traditional material for sealing small vacuum tubes etc is sealing wax, which was used in making the first magnetron). You can pass leads through the Plasticine or through a rubber bung. It is also possible to buy from USA a plastic dome which is a modern equivalent of a bell jar and may be safer. I bought a vacuum pump from a school science supplier. It uses oil and is a rotary vane type I think, and it can get enough vacuum to allow gas discharge experiments. You may be able to measure temperature with a standard thermometer, a thermistor, a temp probe connected to a data logger, or by using IR. I have a diode laser at work which does, I think produce lots of heat, so either give it a big heat sink and/or run it for short bursts.
     
  8. Dec 2, 2018 #7
    A temperature sensor (thermocouple, RTD, etc) bonded to your test article is a pretty standard way to do what you describe (electronics outside the chamber). Harbor freight sells a decent air-motive vacuum eductor - it's a vacuum pump with no moving parts. If you have an air compressor, you're all set.
     
  9. Dec 2, 2018 #8

    berkeman

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    Can you say more about this? There are a number of ways to "control heat dissipation" that don't involve having to pull a good vacuum and deal with the associated complications.
     
  10. Dec 2, 2018 #9

    sophiecentaur

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    @len Are you intending to do a particular experiment of do you want a general bit of tinkering around? (Not being judgemental here; I've done more than my share of tinkering, myself, :smile:) Do you actually need a vacuum or would 'clean (no dust) air do the job? That would be much easier to achieve and would only need a modest vacuum cleaner style system with a HEPA filter to remove dust. What is it about a vacuum that you would need one? The effect of a gas (as opposed to a vacuum) on a laser beam is difficult to measure because the refractive index is so near 1.0 .
    A fish tank would suffice and it would have flat walls (it would collapse with a vacuum).
     
  11. Dec 3, 2018 #10

    Tom.G

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    Harbor Freight also has a small hand operated vacuum pump that will pull a good vacuum in a small working volume of a few cubic inches.

    There is a partial photo of the pump at https://www.physicsforums.com/threa...of-withstanding-a-vacuum.946219/#post-5989953. That photo does not show the handle which is a larger version of a whole-hand trigger as used on a spray bottle. You might also find some other ideas in that thread.

    Cheers,
    Tom
     
  12. Dec 3, 2018 #11

    sophiecentaur

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    @len why does the laser need to be operated inside the vacuum? A laser beam can be aimed through a window in the side of a vacuum chamber and will behave exactly the same as if the laser is operated inside.
    To save yourself money, time and the possibility of unwanted difficulties, it would be a good idea to look again at your proposed experiment. PF could probably help more effectively if you actually describe your experiment.
     
  13. Dec 3, 2018 #12
    I did a lot of thermionic emission experiments in high vacuum during the 60's and even built a glass vacuum system tied to a LN cold trap, diffusion pump, and fore pump and an oven to bake and outgas the glass components. Temperatures were measured with an optical pyrometer and W-Re TC's. Some vacuum equipment was acquired after leaving my day job with the intent of studying electrostatic fusion, but was held off due to time and space constraints. You might be interested in some of this equipment. As was mentioned in the earlier posts, if you would describe exactly the nature of your experiment, we could better advise you.
     
  14. Dec 3, 2018 #13

    sophiecentaur

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    Unfortunately, we know little of the details of the OP's project. Your expertise could be invaluable or, otoh, it could turn out to be a sledgehammer to crack a walnut. We need more input from the OP. What is the relevance of lasers here, for instance?
    Your high vacuum knowledge could presumably be very applicable for a space project.
     
  15. Dec 5, 2018 #14
    For electronics heat dissipation stress tests, you need about ~5kPa or below absolute pressure.
    For me, the most cost-effective (about 200$) solution for this task was following (made a setup back in 2012):

    1) Buy 3 cheap diaphragm pumps from ebay/digikey/sparkfun
    2) Buy at least 1 meter of 5x8mm PVC or silicone tube.
    3) Connect pumps in cascade (input to output) with flexible 5x8mm piping
    4) Wire pumps to single power switch - they may stall if powered separately. The vacuum you will get is 2-5 kPa absolute pressure
    5) Buy large-diameter metal water pipe section with threading from local home center
    6) Buy 2 matching pipe flanges (flat or hemispherical)
    7) Buy a roll of sealing tape - to connect flanges to pipe section
    8) Buy a 1/4 inch or similar "pagoda" (barbed) to threaded type manifold for pipe and T-type barbed manifold for connecting manometer
    9) Buy manometer/vacuum-meter, analog or digital
    10) Drill at least 3 holes in water pipe or one of flanges - for observation window, for vacuum line and for electrical interface.
    11) Glue a piece of thick transparent plastic (poly-carbonate or acrylic) or glass to outer side of observation hole. Silicone adhesive preferable.
    12) Connect pagoda manifold to prepared and threaded hole in pipe or flange. Do not forget to use sealing tape during installation.
    13) Connect manometer to one arm of T-manifold and connect other ends to pumps input and pagoda manifold via flexible tubes.
    14) Pass the bundle of wires through electrical interface hole. Use silicone or epoxy adhesive to preliminary plug hole. Glue few cm of wires to outer wall of pipe to prevent force transfer to plug when you pull the wires.
    15) Apply sealing tape to flanges and seal the vacuum chamber. Switch on the pump.
    16) Eliminate air leaks by applying cyano-acrylate (or other low-viscosity adhesive) to suspicious spots while continuously pumping. Suspicious spots are identified by whistling sound of rushing air.
     
    Last edited: Dec 5, 2018
  16. Dec 8, 2018 #15
    If you are going to use a metal base plate, you can drill and tap your base plate for the pipe thread of a spark plug and use glyptal to seal the threads. Spark plugs make great high voltage feedthroughs. We made some simple vacuum systems with thick-walled, one foot ID glass cylinders and metal plates top and bottom sealed with L-shaped rubber gaskets and vacuum grease. These were used while induction heating refractory metal electron emitters for outgassing before assembly in an emission microscope. They came out really clean. If you are going to heat something to a very high temperature, you will end up plating the inside of your chamber with evaporated material. We used Dawn liquid detergent to initially coat the inside of the cylinders which made them easy to clean up following use.
     
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