经济学人下载:传递热量 良好的传导

Science and technology
科学技术

Channelling heat
传递热量

Good conduct
良好的传导

It may soon be possible to control heat flows with great precision
有可能实现对热流的精确控制

HEAT, as every schoolboy knows, moves in three ways: conduction, convection and radiation.
每个学生都知道热传递有三种方式：传导、对流和辐射。

Convection is the mass movement of a fluid: hot water rising, for example.
对流是液体的整体移动，比如热水上升。

Radiation is simply infra-red light.
辐射只是红外光线。

Engineers know how to control both of these reasonably well.
工程师知道怎样合理地控制这两种热传递方式。

Conduction, however, is most similar to the transmission of sound.
传导很像声音传播。

It is caused, in other words, by atoms vibrating and passing such vibrations on to their neighbours.
换言之，原子震动引起传导，这种震动向邻近物体传播。

Until now, controlling the conduction of heat through solid objects has been a tricky engineering challenge.
时至今日，控制热量通过固体传导对工程界还是一个棘手的挑战。

But, by making the analogy with sound explicit, Martin Maldovan, an engineer at the Massachusetts Institute of Technology, thinks he may have found a way of doing so.
然而麻省理工学院的工程师Martin Maldovan认为自己找到了解决问题的方法，可以使热传导以类似声波传递的方式进行。

Dr Maldovan's invention, published in Physical Review Letters, is based on the idea of a sonic filter.
物理评论快报刊登了Maldovan博士的发明，这个发明基于声音过滤器的理念。

A good way to filter sound—to eliminate certain frequencies while allowing others through—is to transmit the sound waves through a crystal.
这是一个过滤声音的好办法，就是通过水晶传递声波—在消除特定频率的同时允许其他频率通过。

The size of the gaps between the crystal's atoms will govern which frequencies can pass.
水晶原子之间缝隙的大小决定了哪种频率的声波可以通过。

Moreover, the path the sound takes can be controlled by introducing deliberate flaws into the crystal's atomic lattice.
此外，可以在水晶的原子点阵之间故意制造裂纹来控制声音的传播路径。

These flaws act as waveguides, channelling the sound energy along themselves.
这些裂纹起到了波导的作用，声能在裂纹之间传递。

One difference between sound and heat is that most sound waves have low frequencies, vibrating only a few thousand times a second, whereas most heatwaves have high frequencies, vibrating trillions of times a second.
声音传递和热量传递之间的一个区别在于声波的频率低，每秒只震动几千次，而大部分热波的频率很高，每秒震动数万亿次。

In general, low frequencies propagate farther than high ones.
通常低频率比高频率传播的更远。

This is why previous researchers had a difficult time trying to send heat through crystal lattices.
这就是以前的研究者试图在水晶点阵之间传播热能时遇到困难的原因。

Dr Maldovan, however, realised that although most heat is high-frequency, some has frequencies that approach those of sound.
然而Maldovan博士认识到尽管很多热波的频率很高，然而有些热波的频率接近声波频率。

He theorised that if the highest-frequency waves were stripped away, it might be possible to control the remainder.
他的理论是如果把频率最高的热波去掉，其余的热波就有可能得到控制。

To test this idea, he grew crystals of silicon that contained tiny particles of germanium in their lattices.
为了验证这个观点，他研制出了硅晶体，晶体的点阵之间含着细小的锗颗粒。

The layouts of these crystals scattered and blocked high-frequency heatwaves but allowed low-frequency waves through.
散乱的晶体的布局阻挡了高频率的热波，却允许低频率的热波通过。

These remaining waves had frequencies in a range of 100 billion to 300 billion vibrations a second.
这些可以通过晶体的热波的频率范围在每秒震动一千亿次到每秒震动三千亿次之间。

They were still heatwaves and carried warmth, but because their frequencies were lower they behaved much more like sound.
他们依然是热波而且带着热量，但是这些热波的频率比较低，所以它们的传导方式和声音的传播方式就很像了。

And Dr Maldovan could control the heat's path in waveguides as tightly as that of sound waves.
博士Maldovan可以在波导上控制热波的传导途径，使热波传导和声波传导一样紧密。

Though turning these crystals into practical products will require further tinkering, Dr Maldovan thinks they will be immediately useful in the construction of thermoelectric materials, which transform waste heat into electricity, and will ultimately lead to the thermal equivalent of diodes, allowing heat circuits analogous to electrical ones to be built.
尽管把这类晶体转化成实用产品还需要进一步的思考，Maldovan博士认为这类晶体可以马上投入到热电材料的制作上，将废热转化为电能，最后通向热当量的二极管，可以建立和电路类似的热路。

Where that would lead, no one knows.
谁也不知道热路的那一端联着什么。

But it is worth bearing in mind that it was the ability to control convective heat, via the steam engine, which powered the industrial revolution.
但是控制对流热流还是值得我们思考的，因为蒸汽机给工业革命提供了能量。

Controlling conductive heat might have equally unforeseen consequences.
同样，控制传导热流也会带来意想不到的结果。