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?

Where did he say anything about -5 deg?

 

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

You might try building something called a cold finger -- which is pretty much just what it sounds like. One crude way to do it is to simply make a coil of small copper (or other suitable metal) tubing and run cold water through it. The water would flow between the finger and an external unit that would act as a thermal sink. You can monitor the temperature of the water either just as it enters or just as it exits (or both) the coil and use that information to control the fluid flowing in the tube, either by controlling the flow rate or by controlling a cooling unit (such as a Peltier).

 

If the solution doesn't produce heat something like this might work.

Put a Styrofoam lid on that container.
If the subject matter can be placed in a sealed container, you can sink the container to get the uppermost aspect covered with coolant.
If it's buoyant, you can use the lid to force it down to a submerged position.

Where did he say anything about a cup of water?

In the title of the Thread.

Where did he say anything about -5 deg?

Do you have to point out every typo, misinterpretation, and assumption?
Do you have to put it in the form of a question, as if somebody is going to tell you the obvious answer?
Is Alex Trebec coaching you about how you phrase your sentences?

 

One crude way to do it is to simply make a coil of small copper (or other suitable metal) tubing and run cold water through it.

Would that be something like

a water pump using a large reservoir of ice and responding to a thermostat.

 

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

Tim

Cheap -- reasonably so.

But "Peltier" and "efficient" are two words that generally don't appear in the same sentence unless glued together by the word "not".

But unless your solution is producing quite a bit of heat, this probably won't be a huge issue for you.

But you really, really, really need to come up with at least some rough numbers regarding how much heat you need to remove from your chamber (each second).

 

Put a Styrofoam lid on that container.
If the subject matter can be placed in a sealed container, you can sink the container to get the uppermost aspect covered with coolant.
If it's buoyant, you can use the lid to force it down to a submerged position.

In the title of the Thread.

Do you have to point out every typo, misinterpretation, and assumption?
Do you have to put it in the form of a question, as if somebody is going to tell you the obvious answer?
Is Alex Trebec coaching you about how you phrase your sentences?

Given how quick you have been to point out mistakes I have made, that's somewhat a case of the kettle and the pot, don't you think.

I'm sorry you are so offended by efforts to keep people, including myself, on the same page. This is a good example -- since I am no longer seeing the thread title I didn't remember that it mentioned a cup of water there and I was only looking in his posts. So thank you for providing the obvious answer I was overlooking.

 

Where did he say anything about a cup of water?

*deleted* my original comment is no longer relevant

 

Would that be something like

Yes, it would. So sorry that in responding to Post #6 I didn't refer to Post #16.

Since it appears you have a problem with me participating in this thread, I will stop.

 

This site is getting mean. Just sayin'.

 

This site is getting mean. Just sayin'.

I agree. I've tried to bring attention to that in the past.

We're supposed to be here to help other people.

 

Given how quick you have been to point out mistakes I have made

I have been quick to avoid you every chance I get. All I want is to help the TS, not critique every letter and symbol the helpers type, and that's all you did...call attention to every misstep, even if it was a single keystroke. You pointed out a mistake that ronv had already corrected, as if you didn't read the Thread. Then another, which was your own, as if you didn't even read the title of the Thread. Some days you Felix Ungar gets ahead of your Mr. Rogers. I object to unhelpful posts which only focus on the helpers, but I will never object to you helping the T.S.

ps, The pot-kettle fallacy is called, "argumentum ad hominem"
http://sidewiseinsights.blogspot.com/2011/06/pot-meet-kettle-fallacies-part-3.html
By definition, an ad hominem attack in violation of the T.O.S.

 

Hello.

I initially posted the question with the hope that there may be some kind of cooling element or component that can be placed into water and keep the water at a desired temperature. I now realise this is not so simple and because of that I have omitted a lot of variables that I will try to answer below.

> I solution is water.
> I want to keep it at a desired temperature for about 1 hour
> I cannot add anything to the water.
> There is no heat being generated. The water is initially very cold but losing temperature quickly, I guess due to room temp.
> The water is not covered nor can be
> There is no added pressure.
> Forget about the cup. I have a chamber of water with the size mentioned in the first post.
> I have no extra space around the water in order to fit big components such as heat sinks. I could potentially place something in the water or feed tubes into it.

Hopefully this makes it a bit clearer.

Please let me know if it doesn't.

Tim

 

Where did he say anything about a cup of water?

It's the title of the post.

 

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?

Some cups are larger than others. Just like someone´s feet are larger than others´

 

The water is not covered nor can be

That's where most of the heat enters, if I'm right about the container being placed in another container of water.

I have no extra space around the water in order to fit big components such as heat sinks. I could potentially place something in the water or feed tubes into it.

That seems to indicate the large reservoir, mostly filled with ice, and a pump responding to a thermostat.
Even a little bit of insulation around the sides would help. An inch of Styrofoam would be nice, but a quarter inch is still a major improvement over a single wall of sheet metal or a thin glass container.

 

> Forget about the cup. I have a chamber of water with the size mentioned in the first post.
> I have no extra space around the water in order to fit big components such as heat sinks. I could potentially place something in the water or feed tubes into it.

Do you have any space for insulation or maybe a water jacket surrounding the chamber? If you don't even have, say, 1/4", then you're limited to the cold-finger approach, or to operate the entire unit inside a cold room or in a refrigerator.

 

Some cups are larger than others. Just like someone´s feet are larger than others´

Not in my book. A cup in my book is a standardized and well defined unit of volume no different than the term cubic inch or cubic centimeter or US gallon.

When working with physics there is no room for generalizations. Either it is what it is or it isn't.

 

I was once directing a technician running baking experiments in the lab. She kept getting terrible results for what should be a simple - if laborious - process. So I had to go watch her make the bread step-by-step to find where the problem was. When it came time to measure, sure enough, she would use whatever "cup" was handy with no regard to its actual volume.

I always wondered if she was really that stupid, or if this was some kind of protest on her part. I think it was the former.

 

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)

Answer the question guys

[Moderator's note: Intentional insult removed]

 

It was answered already.

A peltier device.

Or an electromechanical device to supply and deliver refrigeration.

There is no magic, available