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No. 273:
Diamonds and Heat

Today, we go from ice to diamonds to ideas. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Diamonds are called ice, but we're also told that you can tell diamonds from glass because diamonds are warm. Actually, diamonds aren't like ice at all. Ice is a good thermal insulator. But diamond is the best natural conductor of heat we know -- three or four times better than copper or silver. Diamonds feel warm because they come up to body temperature so quickly. Diamonds warm up, while glass keeps on feeling cold.

Good heat transfer is highly prized these days. So much energy has to be moved in modern systems. Nuclear reactors put out as much energy as we can carry away. They'd be a lot more effective if we were better at moving energy. The same is true of solar receivers. A field of mirrors focuses the sun's energy on a central tower. We could easily focus enough energy to melt the tower. We're limited only by our ability to carry all that heat away. Super-computers are limited by the need to remove more and more energy from smaller and smaller spaces; and so on.

Modern equipment fairly groans with problems like that, and diamonds -- even commercial diamonds -- are too expensive use on a commercial scale. But during the last few decades a new technology has come into use. It's the heat pipe -- a man-made conductor that carries heat a hundred times better than even diamond.

A heat pipe is a tube whose inner walls are lined by copper-wool or some other gauze-like material. It contains a little liquid -- maybe water, mercury, or alcohol. The liquid evaporates on the warm end. The vapor flows down the middle and condenses on the cold end. The condensed liquid is returned to the hot end by a sort of blotter action in the gauze.

It's amazing how anything so simple works so well. In this case, the inventor is a friend of mine -- a man whose mind I've been privileged to watch in flight many times. In this case I've seen the inventive process that created this new technology.

His name is Lloyd Trefethen. He teaches engineering at Tufts University. Conversation with Lloyd is always a kind of roller-coaster ride. He'll take nothing for granted. He deflects the most straightforward notion so it turns into something else. We were given the heat pipe, where nature left off, because one man simply refuses to see the world the same way each time he looks at it.

Pure invention is ice turned into diamond -- diamond into a heat pipe -- one thing transmuted by a leap in the dark into something wholly other. And it's so exciting to watch happening in another person, or -- better yet -- in yourself.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

J. H. Lienhard IV and J. H. Lienhard V, A Heat Transfer Textbook. 3rd ed., Cambridge, MA: Phlogiston Press, 2004, Click here for a free copy. See especially, pp. 13-16 and Section 9.10.

Note added June 28, 2023: In this episode from 1989, I attribute the heat pipe to Lloyd Trefethen. I have just discovered that R. S. Gaugler patented a heat pipe much earlier -- in 1944. This patent was filed, then long forgotten. Wikipedia also credits one George Grover with inventing it in 1963. I don't have a date for when Trefethen promulgated the idea, but it would be near 1963. It would appear that several people came up with the idea independently.