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

Thread Starter

tim04444

Joined Apr 1, 2016
6
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
 

hp1729

Joined Nov 23, 2015
2,304
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
And keep it water instead of ice? Will adding salt to the water be a problem? Maybe a cold plateand a pressure chamber?
 

Thread Starter

tim04444

Joined Apr 1, 2016
6
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
 

jpanhalt

Joined Jan 18, 2008
11,087
@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:

ronv

Joined Nov 12, 2008
3,770
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
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.
 

Colin55

Joined Aug 27, 2015
519
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.
 

wayneh

Joined Sep 9, 2010
17,496
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?
 

BR-549

Joined Sep 22, 2013
4,928
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.
 

#12

Joined Nov 30, 2010
18,224
@#12 is the resident BTU expert. Let's see what he has to say.
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
 

hp1729

Joined Nov 23, 2015
2,304
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?
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?
 

ronv

Joined Nov 12, 2008
3,770
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
 
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