How can I keep a cup of water at 0-5°C ???

Discussion in 'General Electronics Chat' started by tim04444, Aug 18, 2016.

  1. tim04444

    Thread Starter New Member

    Apr 1, 2016
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    Hello everyone,

    I need to keep a solution that is out in the open (not in a fridge) cold and am not quite sure how to do it.

    The solution will be in a small chamber (2cmx2cmx10cm) and I need to keep it between 0 and 5 °C.

    I can use an arduino to read a thermometer and keep things calibrated, but I'm not sure what to actually use to cool the solution. Are there such things as 'cooling elements' or something like that? I am looking for something relatively cheap (<£40).

    Thanks

    Tim
     
  2. WBahn

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    Mar 31, 2012
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    Is using an ice bath around the chamber an option?

    Look at Peltier devices.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Have you considered just letting ice melt in an insulated container with stirring? In other words an ice-water slush.
    John
     
  4. hp1729

    Well-Known Member

    Nov 23, 2015
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    And keep it water instead of ice? Will adding salt to the water be a problem? Maybe a cold plateand a pressure chamber?
     
  5. wayneh

    Expert

    Sep 9, 2010
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    You might benefit from my "refrigerator" project. But I don't recommend that much of an elaborate solution if you can just set your chamber in an ice bath, or some other simple fix.

    Is there heat being generated in the chamber?
     
  6. tim04444

    Thread Starter New Member

    Apr 1, 2016
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    Hi.

    Thanks for the replies.
    I already have ice in the solution but it is in a situation where it melts quick and I can't top it up easy. I would also like more control of the temperature and for long periods of time. I was thinking of something I could do it in the solution that is cold itself and can be controlled (temperature wise)

    Tim
     
  7. joeyd999

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    Yes. It would violate his specification.
     
    wayneh likes this.
  8. jpanhalt

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    @Post#6
    That is where the insulation comes in to play. A thermos with a mixture of ice and water was used many years ago as our standard temperature for chemical kinetic studies.

    John
     
    Last edited: Aug 18, 2016
  9. ronv

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    Nov 12, 2008
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    Since you have the micro the peltier like post 5 should be pretty easy to implement. We can work that out if you like it.
     
  10. tim04444

    Thread Starter New Member

    Apr 1, 2016
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    Thanks for the replies. I think I may give pelitiers a try. Can you get efficient and fairly cheap peltiers?

    Tim
     
  11. Colin55

    Member

    Aug 27, 2015
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    You have to find how much heat is beging absorbed and relate that to a peltier module. You will need to sit the cup in a tin of water and glue the peltier module to the tin.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    The Peltier will struggle to hold at freezing, assuming ambient temperature for the cooling air. A Peltier can only get to a limited delta T. If you can place the entire assembly in a refrigerator it would it would be easy.

    I'll ask again, is there heat being generated or are we just fighting heat flux?
     
  13. Alec_t

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    Sep 17, 2013
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    Is that minutes, hours, months, .....?
     
  14. ronv

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    I think @wayneh is right. You would need the solution inside an insulated enclosure. Maybe Styrofoam. @#12 is the resident BTU expert. Let's see what he has to say.
     
  15. BR-549

    Well-Known Member

    Sep 22, 2013
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    What is the boiling point and freezing point of the solution? Is it under pressure? What is the specific heat of the solution?

    Are you adding or subtracting energy from the solution?

    How about....what is the solution? And what exactly you are doing with it?

    Perhaps a refrigeration coil in a water bath.

    It's anyone's guess, when we don't know what we're talking about.
     
  16. #12

    Expert

    Nov 30, 2010
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    Well, since you called me out...
    I haven't posted because there are too many variables that need to be dragged out of the T.S.
    Minutes, hours, months?
    Is the heat being generated by the mystery thing that needs cooling?
    Is it a solid, liquid, or gas that needs cooling?
    Is it in a closed container?
    Can it be placed in a closed container?
    Does it have fur?
    Can it defend itself?

    The first thing that comes to mind is that an ice water bath will work very well. If it doesn't last long enough, you're being too lazy or too cheap to build it correctly.
    If a Peltier can't make the Dt, but it's a lot more controllable, use the ice water to heat sink the Peltier.
    Then there is the idea of a water pump using a large reservoir of ice and responding to a thermostat.

    I used to use R-11 to hold at 75 F, but then that ozone thing.:(
    or acetone at 133 F
    n-butane boils at 31.1 F (-0.5 C)
    but every kind of thing that boils near 0 C is flammable and/or toxic, and costs a lot more than water.
    So, it's back to the water pump with a thermostat.

    http://www.engineeringtoolbox.com/boiling-points-fluids-gases-d_155.html
     
  17. tcmtech

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    Nov 4, 2013
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    Well I see a glaring issue with the physics of the concept right there.

    How do yo plan to fit a cup of water (236.588 CC volume) in a 2 x 2 x 10 = 40 CC container? o_O
     
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  18. hp1729

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    Nov 23, 2015
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    I agree on the limitations of Peltier junctions. I never got one down to freezing. It seems a thermos would only keep water down to almost zero. At zero water gets solid. To maintain -5 deg would you need to increase pressure? Maybe a pressurized thermos would work?
     
  19. ronv

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    Nov 12, 2008
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    I was thinking he was keeping his solution in a cups worth of Ice water - so 40 cc of solution in 236 cc of water. If the solution doesn't produce heat something like this might work.
    Since he is doing it with ice water now I'm also guessing the temperature is 0 to +5C and that it has no fur.

    upload_2016-8-18_18-58-18.png
     
  20. WBahn

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    Mar 31, 2012
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    Where did he say anything about a cup of water?
     
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