評論
打印
Science and technology
科學技術
Channelling heat
傳遞熱量
Good conduct
良好的傳導
It may soon be possible to control heat flows with great precision
有可能實現對熱流的精確控制
HEAT, as every schoolboy knows, moves in three ways: conduction, convection and radiation.
每個學生都知道熱傳遞有三種方式：傳導、對流和輻射。
Convection is the mass movement of a fluid: hot water rising, for example.
對流是液體的整體移動，比如熱水上升。
Radiation is simply infra-red light.
輻射只是紅外光線。
Engineers know how to control both of these reasonably well.
工程師知道怎樣合理地控制這兩種熱傳遞方式。
Conduction, however, is most similar to the transmission of sound.
傳導很像聲音傳播。
It is caused, in other words, by atoms vibrating and passing such vibrations on to their neighbours.
換言之，原子震動引起傳導，這種震動向鄰近物體傳播。
Until now, controlling the conduction of heat through solid objects has been a tricky engineering challenge.
時至今日，控制熱量通過固體傳導對工程界還是一個棘手的挑戰。
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.
然而麻省理工學院的工程師Martin Maldovan認為自己找到了解決問題的方法，可以使熱傳導以類似聲波傳遞的方式進行。
Dr Maldovan's invention, published in Physical Review Letters, is based on the idea of a sonic filter.
物理評論快報刊登了Maldovan博士的發明，這個發明基于聲音過濾器的理念。
A good way to filter sound—to eliminate certain frequencies while allowing others through—is to transmit the sound waves through a crystal.
這是一個過濾聲音的好辦法，就是通過水晶傳遞聲波—在消除特定頻率的同時允許其他頻率通過。
The size of the gaps between the crystal's atoms will govern which frequencies can pass.
水晶原子之間縫隙的大小決定了哪種頻率的聲波可以通過。
Moreover, the path the sound takes can be controlled by introducing deliberate flaws into the crystal's atomic lattice.
此外，可以在水晶的原子點陣之間故意制造裂紋來控制聲音的傳播路徑。
These flaws act as waveguides, channelling the sound energy along themselves.
這些裂紋起到了波導的作用，聲能在裂紋之間傳遞。
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.
聲音傳遞和熱量傳遞之間的一個區別在于聲波的頻率低，每秒只震動幾千次，而大部分熱波的頻率很高，每秒震動數萬億次。
In general, low frequencies propagate farther than high ones.
通常低頻率比高頻率傳播的更遠。
This is why previous researchers had a difficult time trying to send heat through crystal lattices.
這就是以前的研究者試圖在水晶點陣之間傳播熱能時遇到困難的原因。
Dr Maldovan, however, realised that although most heat is high-frequency, some has frequencies that approach those of sound.
然而Maldovan博士認識到盡管很多熱波的頻率很高，然而有些熱波的頻率接近聲波頻率。
He theorised that if the highest-frequency waves were stripped away, it might be possible to control the remainder.
他的理論是如果把頻率最高的熱波去掉，其余的熱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.
為了驗證這個觀點，他研制出了硅晶體，晶體的點陣之間含著細小的鍺顆粒。
The layouts of these crystals scattered and blocked high-frequency heatwaves but allowed low-frequency waves through.
散亂的晶體的布局阻擋了高頻率的熱波，卻允許低頻率的熱波通過。
These remaining waves had frequencies in a range of 100 billion to 300 billion vibrations a second.
這些可以通過晶體的熱波的頻率范圍在每秒震動一千億次到每秒震動三千億次之間。
They were still heatwaves and carried warmth, but because their frequencies were lower they behaved much more like sound.
他們依然是熱波而且帶著熱量，但是這些熱波的頻率比較低，所以它們的傳導方式和聲音的傳播方式就很像了。
And Dr Maldovan could control the heat's path in waveguides as tightly as that of sound waves.
博士Maldovan可以在波導上控制熱波的傳導途徑，使熱波傳導和聲波傳導一樣緊密。
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.
盡管把這類晶體轉化成實用產品還需要進一步的思考，Maldovan博士認為這類晶體可以馬上投入到熱電材料的制作上，將廢熱轉化為電能，最后通向熱當量的二極管，可以建立和電路類似的熱路。
Where that would lead, no one knows.
誰也不知道熱路的那一端聯著什么。
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.
但是控制對流熱流還是值得我們思考的，因為蒸汽機給工業革命提供了能量。
Controlling conductive heat might have equally unforeseen consequences.
同樣，控制傳導熱流也會帶來意想不到的結果。
