1
$\begingroup$

Salt is used to lower the melting point of ice. This is often used when making ice cream, as 0°C isn't cold enough to freeze some of the creams and fats present.

I need to transport a frozen item for about 3 hours. I was thinking of ways to keep it below 0° beyond a simple ice cooler. I do not have access to dry ice, so my next best thought was to add salt to the ice in the cooler.

The salt melts the ice into liquid water and lowers its temperature. This would mean that the beginning temperature(s) of the item would remain colder than with ice alone (note: the item is coming from my freezer which is currently set to the lowest setting). Melting is also cooling process, which would keep the item colder.

However, after extended periods of time, would the benefits begin to wane? Would having only ice keep the item cooler for longer? Saltwater does warm faster than fresh water, and I'm not entirely sure if ice and air would insulate the item better than water.

Thank you in advance for your input!

$\endgroup$
2

1 Answer 1

1
$\begingroup$

Salt does not lower the temperature, but only the melting point. So your ice will more easily melt if you salt it, which means that you will likely have a cooler full of salty cold water in short order. Because the liquid will be in stronger thermal contact with the edges of your cooler, and your cooler is not perfectly insulated, this will likely increase the rate of temperature change. Over the course of only 3 hours, I recommend just using regular ice in a decent cooler, as this will likely be perfectly sufficient to prevent any issues. Plus, you don’t have to deal with the salty mess after the fact, which may or may not be an important factor for you.

$\endgroup$
3
  • $\begingroup$ "Salt does not lower the temperature, but only the melting point." Anything that promotes melting causes a greater rate of latent heat absorption, which does indeed cool things down more. The practical optimization of this result is a question for Engineering Stack Exchange. $\endgroup$ Commented Mar 13 at 3:39
  • $\begingroup$ See "Why does ice water get colder when salt is added?". $\endgroup$ Commented Mar 13 at 14:43
  • $\begingroup$ My point is that the salt does not really cause a change in temperature directly (apart from entropically), but it certainly does change the rate at which the temperature does change, as you mentioned. $\endgroup$ Commented Mar 13 at 16:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.