Cooling Coffee
冷却咖啡
How do you get your coffee cool enough to drink in the shortest possible time?
如何在最短的时间内将咖啡冷却到可以饮用的程度？
Leave it black for a while, then add cream.
放一段时间让它保持黑色，然后加奶油。
The heat loss rate by conduction, convection, and radiation all depend upon the difference in temperature between the hot object and its surroundings. Therefore the cooling rate is greater before you add cream. Also, the rate of evaporation from the coffee is greater if you leave it hot for a time, and evaporation is a potent cooling mechanism since the evaporating water must extract its large heat of vaporization from the remaining liquid. All these mechanisms cool the coffee faster before you add cream.
通过导热、对流和辐射的散热速率都取决于热物体与其环境之间的温度差。因此，在加奶油之前，冷却速率更大。此外，如果让咖啡保持热的时间更长，其蒸发速率也会更大，而蒸发是一种有效的冷却机制，因为蒸发的水必须从剩余的液体中提取大量的汽化热。所有这些机制在加奶油之前都能使咖啡冷却得更快。
| An often cited but bogus reasoning in this example is to say that black objects radiate better than white ones. This is true for visible light, but this radiation is in the infrared where the visible color is not expected to be a significant factor.
在这个例子中，有一种常被引用但错误的推理是说黑色物体比白色物体辐射得更好。这在可见光范围内是正确的，但这种辐射发生在红外区域，而可见颜色在该区域并不应成为显著因素。 |
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| Heat Questions
热学问题 |
Heat concepts
Heat transfer concepts
索引 热学概念 热传递概念
| HyperPhysics***** Thermodynamics
HyperPhysics ***** 热力学 | R Nave |
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