Question: What is the best way to melt ice?
No, pressure should be increased to melt ice. But I calculated this effect is to weak to achive impressing results: about 5*10^-5 of the mass of ice will melt for each bar of pressure increase.
This metod would make sense only if we were limited to very short times.
I cannot show that increasing pressure will work better than decreasing pressure, but I can explain why increasing pressure leads to melting :
You can see on this diagram that when you are bellow the triple point temperature and around the 1 kPa, increasing the pressure will lead to melting. But it only works for water.
As I've said, I don't know which way is the fastest.
Ok why would increasing pressure work better than decreasing pressure and heating? Not sure I get that?
Thank you very much for the comments. Changing the pressure would be best, but unfortunately, we can't use any external source. The only external sources we can use are the room temperature and gravity for instance.