昇華是指一种物质从固态不经过液态直接转化为气态的过程，是物质在温度和气压低于三相点的时候发生的一种物态变化。与昇華相反的过程称做凝華，指物质从气态直接变成固态。這樣的例子有結霜。昇華是吸熱的反應，所需的熵是汽化熱和熔化热之和。
Frost-free freeze physics--it's more than a tongue-twister(绕口令).
“Sublimation” is when ice turns into a gas without passing through the usual intermediary liquid state. If you leave your ice cubes in back of the freezer for a month or so, you might notice they start to shrink. That’s because they are sublimating: the ice is turning to water vapor even though it never melted.
But I tried this experiment myself and my ice cubes never shrunk! All I got was a cold head! Then, physicist John Carini explained to me that it only works if you have a frost-free freezer.
Why is that?It’s in the nature of sublimation. When we say that ice can turn into water vapor, what we mean is that (1)fast-moving water molecules can actually (2)fling themselves off the surface of the ice cube and into the surrounding air. That’s what evaporation means. The more molecules that can free themselves of the ice this way, the more the ice has turned into vapor.
But wait!In order to do that, the air around the ice cube can’t (3)be saturated with water already. If it is, there’s no room for more molecules and evaporation can’t take place. Frost-free freezers keep the air from becoming saturated so that it won’t freeze on the walls. But that also means ice-cubes can sublimate nonstop!
Notes:
(1)fast-moving adj.移动迅速的
Candy as a fast-moving consumer goods, products price is not high, still attracts the public consumption.
糖果作为快速消费品，公司产品单价也不高，仍然吸引着大众消费。
(2)fling off发出;甩掉;挫败
It's good to fling off heavy clothing now that spring is here.
春天来了，脱掉厚厚的棉衣是适时的。
(3)be saturated with 被…所饱和;充满着
Permit this entire period of time to be saturated with BLUE LIGHT.
这段期间，让蓝色之光充满你的整个存在。
