r/AskScienceDiscussion • u/SubstantialNumber570 • 6d ago
General Discussion Thermodynamics
So I have a question about ice. Does ice melt at an exponential rate because as it melts there is less “cold” or does the shrinking surface area cancel that out? Like does it work like the reverse of icicles forming or is that effect negated by the shrinking surface area that is exposed to the ambient temperature? Idk I don’t do thermodynamics so if someone does could you answer this. Feel free to call me dumb if this is a stupid question.
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u/SmorgasConfigurator 6d ago
Despite its name, this question is not primarily about thermodynamics, but about heat transfer.
Your intuition about surface area is correct. When heat enters or leaves an object it does so through the surface between the object and surrounding. So the rate of heat in this case melting the ice will depend on the surface area multiplied by some inherent material heat rate coefficient.
The latter coefficient (which is a topic of thermodynamics) complicates things a bit. If you take an ice cube and you place it in water at 5C, versus, you place the identical ice cube in air at 5C, which melts quicker? Intuitively, the ice cube in water melts quicker. The reason is that air is a poor medium for heat transfer. So although the ice cube surface area is the same, the rate coefficient is greater for the case of ice in water.
I note that because as ice melts, it matters what happens with the melted water. If it stays with the ice, as if in a puddle, you effectively increase the surface area through which the ice-water system exchange heat with the ambient air. So melting implies more area. If the water is removed, like the dripping icicle, then the surface area for the ice decreases. So melting implies less area.
So predicting actual rates of melting a particular ice system, you need to consider many additional parameters.