Sciencemadness Discussion Board

How to maintain 0C Cooling Bath for 12 hours?

beerwiz - 11-10-2018 at 07:45

How can you maintain a 0C cooling bath for 12 hours?
Using ice and salt will only be good for an hour or so then the ice melts.

What is the solution to this other than babysitting it and adding ice constantly?
I thought about putting it in the refrigerator and the stirrer with the power cable coming out of the refrigerator door but that would break the seal and the temp would go up.

Sigmatropic - 11-10-2018 at 08:06

Either a cool chamber, also know as a walk-in fridge. Or a Styrofoam box packed with ice. Each has their benefits, either having a constant supply of cold beer and the other one, well, it's low cost.

Sulaiman - 11-10-2018 at 09:14

What volume of item to be cooled ?
How important is 0.0oC ?
Does the cooled item produce or absorb heat ?

macckone - 11-10-2018 at 12:07

You can buy thermoelectric coolers that are portable:

https://www.thecoolerzone.com/best-thermoelectric-cooler/

You can also make your own using a PID controller and peltier coolers:

https://www.amazon.com/TEC1-12706-Thermoelectric-Peltier-Coo...

Magpie - 11-10-2018 at 13:00

Use acetone/dry ice in a styrofoam cooler or Dewar. This can be as cold as -80°C.

Sigmatropic - 11-10-2018 at 13:04

Acetone in a Styrofoam box? surely I'm missing something here, but yeah I heard colleagues who put a mix of ice and dry ice in a styrofoam box say it was still cold after the weekend.

XeonTheMGPony - 11-10-2018 at 15:37

get a free water cooler, the type with pipes in the back, a bit of wiring and poof you have temp controlled water bath.

good for about 50 to 60w heat dissipation, more heat temps will climb.

Herr Haber - 12-10-2018 at 03:18

Beerwiz heh ? :)

Go to a bar, order a beer, ask how they made it cold.

Joke aside, you can easily find cooler units, dismantle them and take what you need. Ebay works too.
9/10 of these units are not designed for 0 degrees or negative temperatures. But if you slow the flow with a smaller pump than required and chose the right liquid...

XeonTheMGPony - 12-10-2018 at 03:47

They can go to -20, it is the question of thermostat and heat load, more heat it will start to rise as you exceed the compressors ability to pump the heat.

DavidJR - 12-10-2018 at 04:30

If the reaction is exothermic a fridge or freezer may not be able to cope. Remember what a fridge is fundamentally - an insulated box. Insulation avoids wasting energy in normal usage of the fridge, and means the cooling system only has to be able to remove heat at a relatively slow rate. If you put something in which is not merely hot but also actively generating heat, then you may overwhelm the cooling ability of the fridge, and given that it is an insulated box, it may actually end up resembling an oven more than a fridge.

Ubya - 12-10-2018 at 07:15

Quote: Originally posted by DavidJR  
If the reaction is exothermic a fridge or freezer may not be able to cope. Remember what a fridge is fundamentally - an insulated box. Insulation avoids wasting energy in normal usage of the fridge, and means the cooling system only has to be able to remove heat at a relatively slow rate. If you put something in which is not merely hot but also actively generating heat, then you may overwhelm the cooling ability of the fridge, and given that it is an insulated box, it may actually end up resembling an oven more than a fridge.


a fridge is insulated to be more efficient, you could have the compressor run all the time OR run it for 30 minutes a day and still have the same inside temperature.
same reason why an oven is a closed box, less heat dissipation=less power needed

macckone - 12-10-2018 at 08:11

The peltier cell I linked is 92W heat removal at room temperature.
You can fit four on a container to fit an average 500ml flask.
The larger the flask and outer container the more you can fit.
You need a heat sink and fan for each one.
Regulating the voltage regulates the temperature.
With a PTD-100 probe and PID controller, you should be able to maintain within .2C
Peltier cells can also be used for heating under 60 or 70C.

Heptylene - 20-10-2018 at 12:36

Quote: Originally posted by macckone  
The peltier cell I linked is 92W heat removal at room temperature.
You can fit four on a container to fit an average 500ml flask.
The larger the flask and outer container the more you can fit.
You need a heat sink and fan for each one.
Regulating the voltage regulates the temperature.
With a PTD-100 probe and PID controller, you should be able to maintain within .2C
Peltier cells can also be used for heating under 60 or 70C.


92 W is the peak power consumption, but the efficiency of heat removal is pretty poor usually right?

You'll have a bit more than 92 W of heat to dissipate per element, hence the need for a heatsink as you said.

macckone - 20-10-2018 at 16:38

QMax is maximum heat removal not power consumption at a 65C - 70C Tdiff. If you can keep the 'hot' side cooler, it will increase the heat removal. QMax of the peltier cell is listed as 92W. But it also lists it as 60W. I suspect it is actually 60W and the power consumption is 92W. So the ad is incorrect, which is not at all unusual.

Heptylene - 21-10-2018 at 06:08

Quote: Originally posted by macckone  
QMax is maximum heat removal not power consumption at a 65C - 70C Tdiff. If you can keep the 'hot' side cooler, it will increase the heat removal. QMax of the peltier cell is listed as 92W. But it also lists it as 60W. I suspect it is actually 60W and the power consumption is 92W. So the ad is incorrect, which is not at all unusual.


If it can really move that much heat it could be a good building block for a recirculating chiller. Putting a few of these with large heatsinks and fans should be easy enough. I wonder if the advertised specs are real or inflated.

kulep - 21-10-2018 at 06:37

Quote: Originally posted by macckone  
QMax is maximum heat removal not power consumption at a 65C - 70C Tdiff. If you can keep the 'hot' side cooler, it will increase the heat removal. QMax of the peltier cell is listed as 92W. But it also lists it as 60W. I suspect it is actually 60W and the power consumption is 92W. So the ad is incorrect, which is not at all unusual.


Peltier's efficiency is way worse than that, ~60w is the power draw @12v and the cooling capacity is very bad, also you should run them at constant current, not voltage. I've read somewhere that running many modules in parallel at low current is more efficient but I'm not so sure.

Another problem is that the hot and cold side are millimetres apart, where in a phase change system that's not the case.

https://www.youtube.com/watch?v=5cFJJeacJOc here's a nice vid

[Edited on 21-10-2018 by kulep]

S.C. Wack - 21-10-2018 at 08:42

Could one put a hole, and a hose, on the side of a styrofoam bathtub? For the coolant returning by gravity to the suitably sized ice chest, featuring a fountain pump (everyone here should already have at least two?) inside? Using ice instead of Peltiers? Then use the freezer to make more ice?

macckone - 21-10-2018 at 11:31

Kulep: modern peltier coolers usually run at about 1.5x the heat removal. For the cell in question they state 92W QMax but the actual power is 15.4V@6A (92W) so the first line stating 60W is probably the actual heat removal at that voltage and amperage.

Wack: You could use an ice chest or a trash can if you have one big enough. It will take longer than 12 hours to melt half of a 50 Gal trashcan filled with ice which holds about 20 x 10lb bags.