I have injectable medicine that I need to refrigerate. Sometime when I travel I have to keep it in a thermos. Currently I insert a plastic jar with a lid that contains frozen water in it that I put into the thermos (the jar size is O.D. is 3" tall with a 1.7" Dia.) . The thermos size is I.D. is 4.5" tall with a 2.65" Dia. I use the jar so the liquid won't slosh around. The vial is 1.5" tall with a .625" Dia. that I wrap with bubble wrap so it wont move around in the Thermos. But what if I took a piece of some type of metal, that does not rust, and made it to fit to the inside of the thermos with a hole in it big enough to hold the vial. Could a piece of metal, that is put into a freezer then put into the thermos, keep the vial cool for as long if not longer than the jar with frozen water. And what type of metal would be the best for retaining coolness in a thermos.
1 Answer
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Fitting metal into the thermos flask risks breaking the fragile glass container, unless you also wrap the metal in bubble wrap.
Metals typically have thermal heat capacities much less than water - eg copper 0.4 J/gK compared with 4.2 J/gK for water. This means that water requires 10x as much heat to raise it by the same temperature - it is 10x more effective for storing heat or cold. So you are much better off using water to keep the vial cold.
The advantage of water is increased 100x again if the water is frozen or partially frozen, because it requires 336 J/g to melt ice. Below room temperature there is no equivalent for metals, which are already well below their melting temperatures : they are already "frozen".
answered Mar 26, 2017 at 1:20