Science Buddies: "Ask an Expert"

If I was to have a question like "How to slow down the melting rate of ice by using reflective (such as flasks) containers?" What materials should I use to test it out?

Hi SpringFrost,

Welcome to the Ask an Expert Forums. Just to make sure I understand your engineering goal - you want to engineer a device that will reflect light off of containers so that ice will melt at a slower rate, correct? There are a couple of aspects to this problem. (1) Things melting and (2) reflecting light (or, as we shall see), minimizing heat transfer.

When you take an ice cube out of your freezer, its temperature is lower than 0 degrees Celsius. If put that ice cube on the counter, which is (hopefully!) warmer than the freezer, heat will flow from the warm counter into the colder ice cube. The additional heat will increase the ice cube's temperature, but the ice will still be ice until the ice cube's temperature reaches 0 degrees Celsius. That's when (assuming you have pure water ice), the ice begins to melt. If your ice has impurities (e.g., salts) in it, it will melt at a lower temperature. (This is why you put salt on icy sidewalks - the salt makes the ice melt, even when it is less than 0 degrees Celsius outside.) As the ice melts, its temperature will stay a constant 0 degrees Celsius. Then, once all the ice has melted, the temperature of the meltwater will start to increase. So, when you are talking about either delaying or slowing the melting of ice, what you want to do is to slow down the rate at which heat is transferred from the surroundings to the ice cube. You can kind of think of this as slowing down how fast the temperature of the ice cube changes.

Take a look at this article about thermoses (or vacuum flasks) work. It discusses heat transfer and describes how thermoses minimize heat transfer to keep things either hot or cold. The principles discussed in this article are the principles you should think about as you engineer your device.

http://home.howstuffworks.com/thermos.htm

In addition to reflectivity, you may also want to think about including insulation in your device (see the thermos article).

For materials, I suggest selecting two or three materials that you think might be good reflectors. Aluminum foil might be a good option to test. You could also choose two or three different insulating materials. Try different combinations of reflecting and insulating material until you find the combination that works best. In addition to the material you use, the design of the device will affect how well it minimizes heat transfer, so you'll want to explore different designs, too. Remember to keep your variables controlled: when you compare materials, make sure you use the same design; when you compare designs, make sure you use the same materials. That way you isolate the independent variable you are interested in.

Good luck in your engineering! Let us know if we can help with anything else.