Arduino compact air vaccum pump

Hello,
I have a sealed jar of 2L that I would like to cool to -100°C. Because the temperature may change, I want to use an arduino that will turn the pump on and off in order to change the temperature whether it should be -100°C or 0°C. I read about the perfect gas law and came to the conclusion that I needed a pressure of 6mbar to reach -100°C.

Would you know a vaccum pump that can be monitored using an arduino and that can help me reach 6mbar inside the jar? I have seen many vaccum pumps but they are all really expensive and huge but since my jar is only 2L of volume I hope that there might be another choice.

Looking forward for your answers,
Thanks!

I don't know what you mean by an Arduino monitoring a vacuum pump. It can operate a relay to turn the pump on and off.
I just checked my 12 volt emergency air compressor. I bought it 30 years ago at a yard sale. It was new in the box. Made in Canada, called "grasshopper". I have use it in emergency several times.
It has an input that is a standard pipe thread, so a copper tube could be connected and then it will become a vacuum pump.
Look at all the 12 volt air pumps you can find and see it any have a standard pipe thread input port.
Paul

Thanks for your answer. I edited the question to be clearer about the term « monitor ». I cannot find any 12V pump that can pump until 6mbar…

Likely due to the pump valves sealing the vacuum can only do so much. So begin looking at the design of the valves. Cheap ones are spring steel covering a rubber gasket.
Paul

What do you call "really expensive" and "huge"? You could try this $70 one:

I'm no physicist but I don't think that is how the "Ideal Gas Law" works.

"pV = nRT" (pressure in Pascals times volume in cubic meters) = (moles times a constant times absolute temperature). You can't change the temperature with a vacuum pump. You will reduce 'n' and therefore 'p' but not T.

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I see… so would there be kind a of an arduino component that may compress the air? Until the pression reaches 6mbar as before.

Thanks for your answer!

Hi,

Sorry but you need to research pressures and vacuums.
You will NOT be compressing to 6mbar, you will be creating a LOWER PRESSURE down to 6mbar from atmospheric, 1023mbar.
BUT
As @johnwasser has explained, your method has flaws.

Arduino is programming and electronic hardware, not laboratory pump equipment.

What is the purpose of your project?

Tom... :smiley: :+1: :coffee: :australia:

I would like to recreate kind of a spatial atmosphere (like mars one for instance). It’s kinda crazy i know :wink:

I thought about something: what about using a vacuum pump to take all the air out so my 3L jar is « sous-vide » and the pressure is 0 (idk if it’s true) and then I use the arduino to add gas in the jar till the pression hits 6mbar.

Would this be possible?

Please investigate further on what you are proposing. The glass jars I am familiar with cannot and will not withstand much vacuum. Glass jars made for vacuum are very thick. Then there is the problem of sealing what ever tubing you are using to connect the jar to the pump.
Be careful!
Paul

When you compress air in your bicycle pump it gets hot. Therefore when you rarefy air it gets cold. The problem is you can't really use it to control temperature because of heat flow into or out of the chamber. That is, your bicycle pump soon cools off again even if you keep the air inside compressed because it radiates and convects heat to the atmosphere.

Compressing air in a cylinder increases 'p' and reduces 'V'. If 'p' increases more than 'V' decreases the left side of the equation (pV) goes up so the right side of the equation also goes up. Since the number of molecules ('n') has not changed, the temperature ('T') has to go up ('R' is a constant).

Rarefying air will reduce the temperature IF you increase the volume without changing 'n'. Pumping molecules out of a fixed 'V' container changes 'n', not 'T'.

I know, don’t worry! I’m using the word jar to make it easier tu visualise but I won’t use a simple glass jar for this experiment (if it is theoretically possible)

Ah, yes - thanks, John. :slight_smile:

Then give the specifications for your jar. As I recall from chemistry labs so many years ago, the bell jars for vacuum were about 1/2 inch thick.
Paul

Oh sorry, at first, the subject was about a vaccum pump that would work with arduino but then johnwasser explained that using a vaccum pump to take air out will only change n and not T…

Now we are quite off topic but I need to find out more about lowering the pressure without changing n

Are we going in circles? n is the number of molecules of gas in your jar. How will you pump them out to make a vacuum without reducing the number of molecules?

Getting a high vacuum (close to zero pressure) is MUCH more expensive. You need something like the diffusion pumps used to do the last bit of pumping on an electron microscope. Six millibar (610 Pa) is MUCH easier and cheaper. You should mix the atmosphere first and then reduce pressure. For Mars you want:

  • Carbon dioxide: 95%
  • Nitrogen: 2.8%
  • Argon: 2%
  • Oxygen: 0.174%
  • Carbon monoxide: 0.0747%
  • Water vapor: 0.03% (variable)

You could probably get close enough by adding enough Dry Ice to bring the air in the box up to 95% CO2.

I think you will need active refrigeration to get the temperature down to Mars levels (-75 to 0°C). Perhaps some Dry Ice (-78.5°C) under your container would get you close enough.

But to mix the atmosphere correctly I need to first vaccum all the air inside the jar so I can start with blank basis? Cause if I don’t there will be a lot of dioxygene :confused:

Besides, if I manage to recreate the great composition of the atmosphere, how am I supposed to lower the pressure as wells as to keep the same composition of atmosphere? The pump will for sure vaccum a great part of my gas?

Finally, you would advice to lower the temperature using dry ice instead of pression?

Thanks for your help :blush:

Going back to the original question, the way air is normally cooled (so individual gases can be extracted) is by compressing it first. It is held compressed until the heat has dissipated and the temperature is back to normal, and then it is quickly decompressed (increasing V, but keeping n constant). This causes the temperature to plummet to levels a long way below 0C.

I think if you want to maintain your air at -100C you're going to need a supply of liquid nitrogen.

No, you only need to reduce the volume of the unwanted gas to a level you desire. You can do this by chemical reaction means or by filtering.
Paul