Thermal Insulation for Keeping Liquid Cold - 65 characters

[Usjes]

Hi,

I am trying to keep a small vial of liquid cold (> 2 Celcius but < 8 Celcius) for 10 hours when the ambient temperature is 20 -> 30 Celcius. So if I'm making a container to hold it I'd like to know what is the best material to use. My initial thought was to simply place it in a thermos flask along with a frozen gel pack. Is the semi-vaccuum of a thermos flask the most effective insulator or could some other material like poly-styrene perform better? I am not interested in expensive specialized materials but rather a general comparison among the materials that would be available in an average household or you would find in the average hardware store.
So does anyone know?

Thanks,

 

[edgepflow]

Try a thermos in good condition and put 1/2" to 1" thick of fiberglas or duct wrap insulation on sides, top, and bottom. Make sure the insulation is tight against the thermos and does not have gaps and openings.

 

[xts]

Put your vial into a small styrophoam container, filled up to the max with 8C water. And then put this small container into the big one (also styrophoam), filled with crushed ice at 0C.

If you accept your liquid may drop below 2C (just above 0C) - put it directly into styrophoam container with water with ice.

 

[Naty1]

You can get some basic ideas here:

http://en.wikipedia.org/wiki/Thermal_insulation

Some conceptual ideas here:
http://en.wikipedia.org/wiki/Thermos

R values for some materials here:

http://en.wikipedia.org/wiki/R-value_(insulation)#Typical_per-unit-thickness_R-values_for_material

 

[Usjes]

Thanks for the R-values Naty1, these seem to be the most relevant info and they basically confirm that I was thinking, that for a given coolant (eg. adding ice or water or frozen gel-pack) the best insulator will be a thermos flask. Judging by the listed values it will be significantly better than anything else I can get my hands on.

 

[xts]

R-values are not the only important point. In a styrofoam box of few litres you may keep ice/water for much longer than 10hrs - so it makes no big difference if you use thermos or such box.
What I see most difficult is that you wish to keep your vial in 2-8 C span - it may be difficult to make it just above 2C rather than just above 0C available with ice/water. There is no easily available (and safe - using boiling butane is not a good idea...) substance having melting or boiling temperature between 2C and 8C

 

[Usjes]

I'm trying to minimize the overall volume of the container to be as portable as possible, hence my preference for the highest R insulator. Also the contents won't be homogenous, ie. I will have a small vial of liquid (1mL) in a 350mL thermos and then some form of frozen gel-pack. The vial can will be ~2 or 3 Degress C when inserted and I am hoping the the average temp of vial+frozen coolant + air inside the thermos will remain in the range 2 -> 8 degrees.

 

[xts]

If the temperature lower than +2C may damage your sample - such solution is not safe.

I would advice to fill the thermos with a water at 7C or so, to increase the heat capacity of your sample. Then put such thermos inside the cooling box with gel-packs or melting ice. Gel-packs (as those for tourist cooling boxes) stabilise the temperature on about -5C.Melting ice is not much less efficient, but stabilize temp on 0C.

 

[Usjes]

Okay so I did a triall run with a small cooler bag + Gel packs (2) and your predictions proved eerily accurate xts. See the attached plot. The temperature did bottom out at about -5 Degrees. Clearly there is a very steep drop in temperature at the start which will ruin my sample so now I am wondering what I can do about this. Specifically I am wondering what the impact will be if I now insulate the sample itself before placing it in the cooler between the two gel-packs?
I am hoping that such insulation will lower the heat transfer rate from the sample and thus smooth out the sudden spike down to -5 near time zero while minimizing the decrease in the overall time that the sample remains below 8 Degrees. Can this work ? Or will the entire plot just move up vertically if I isulate the sample before placing it in the cooler?

 

[xts]

That is what I already adviced you: to insulate your sample. But you should not only insulate it, but also increase its heat capacity. It means: put the vial to insulating mini-box (mini-thermos) not alone, but together with some water of appropriate temperature (near upper limit acceptable for your sample).
I also advice to use melting ice rather than gel-packs. Gel-packs produce -5C, while ice only 0C. At the most dangerous moment, when your sample is just above its mininimal temperature +2C, heat flow to melting ice would be 3 times slower (temp. difference 2C) than to gel-packs (temp difference 7C).