2
$\begingroup$

Suppose you have a container with a drain at the bottom full of frozen H2O which you leave a room temperature to melt. Will the ice melt faster if you drain the water as it melts?

I would expect that the water, being warmer than the ice, will speed the melting of the ice. However, I would also expect that draining the water would remove allow more air to enter the system and heat the ice faster. Which explanation is correct?

Related question: if the container is a cooler to fill with warm beverages, will the beverages cool faster in a wet or dry ice-filled cooler?

Improve this question
$\endgroup$

2 Answers 2

Reset to default
6
$\begingroup$

Assuming the water and air are the same temperature (and that the air is mostly stationary) then the ice will melt quicker in the water. This is due to water having a higher thermal conductivity and heat capacity. In fact, this is easy to test: place a cocktail stick through an ice cube and lay it on top of a glass filled right to the top with (room temperature) water. The submerged half will melt quicker than that on top.

Regarding the second question: A warm object will cool quicker in icy water than in just ice for the same reason above but also because of increased surface area contact. However, icy water will be warmer than just ice. So the item will potentially be able to achieve a lower temperature in just ice (slow and steady wins the race).

Improve this answer
$\endgroup$
4
  • 1
    $\begingroup$ I think the main property at play is the thermal conductivity, rather than heat capacity. The faster the medium can conduct heat to the ice, the faster it will melt. $\endgroup$
    – buckminst
    Commented Jul 29, 2014 at 19:13
  • 1
    $\begingroup$ Assume that the water is colder than the air because it is recently-melted ice and no room-temperature water has been added to the ice. $\endgroup$
    – Slavatron
    Commented Jul 29, 2014 at 19:17
  • $\begingroup$ @buckminst You're right, both are relevant - I've corrected the answer. $\endgroup$
    – lemon
    Commented Jul 29, 2014 at 19:23
  • 1
    $\begingroup$ Actually, the water is the same temperature as the ice, at the melting point. Any heat transferred into the water gets transferred to the ice for it to melt. So any ice in the container will melt where the heat is applied. Your example of an ice cube on a cocktail stick is not correct since the water in the glass is not at the freezing/melting point. So the ice melts fast to cool the water down to the freezing/melting point. $\endgroup$
    – LDC3
    Commented Jul 30, 2014 at 0:49
1
$\begingroup$

The ice in the drum will melt faster if the water is not draining out.

This is because any air space between the drum and the ice slug will be a good insulator.

As mentioned in a comment all the water will remain at 0 °C until all the ice is melted. Heat from the outside will cause convection currents in the water and transfer heat faster to the slug and melt more. Keeping the water in will allow for a maximum of drum surface in direct contact with the internal cold water and maximise the external heat transfer.

There is an added bonus if the drum is full, the ice slug will soon float free and rise up to touch the lid and gain further external surface area to assist with melting at the lower bulk ice temperature witch will have a slightly better thermal gradient and so be faster.

If the air is cold but the floor is hot then heat is mostly transferred through the bottom then it will be faster to drain the water.

Bonus answer:

In a cooler you want the maximum of cold thermal mass but the minimum of heat transfer. As the sides are an insulator the thermal mass is an advantage. If the sides were not an insulator like a tub or a drum then draining the water away from the warm tub walls is advisable but will only help while the ice has not melted to conform to the tub shape. The problem is that after the ice has melted you no longer have the small benefit of the cold water (that you drained). This means that you need to insulate to slow the heat flow and gain the benefits of the ice and the water. Using a foam yoga mat inside or outside the tub will improve things a lot in conjunction with some wood under it.

Keep in mind that melting ice is MUCH better at keeping drinks at 0 °C than water at 0 °C. Also ice water slurry is ideal for fast cooling of a warm beverage thrown into a tub or cooler as the water absorbs the heat faster due to better surface contact.

Improve this answer
$\endgroup$

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.