What I've Learned

In air, the faster the air molecules are moving, the higher the temperature, right?

Well, sort of.

Actually, air temperature is the average of fast and slow moving molecules. The higher the average speed of the fast and slow, the higher the temperature. If there were a way to separate the faster moving molecules from the slower ones, you could have a stream of hot air and a stream of cold air.

There is a way.

In 1933, French physicist Georges J. Ranque invented a tube that could spin gases.

In the 1940s, German physicist Rudolf Hilsch improved the design, calling the devise a Wirbelrohr (whirl pipe). He tried to use it to create a superior refrigerator system, but couldn't make it more efficient than models then in use.

The Ranque-Hilsch vortex tube (I like Wirbelrohr better) has since been used to separate gas mixtures. For example, oxygen and nitrogen or carbon dioxide and helium.

The excellent thing is, it will also separate hot air from cold. Here's how.

Air is forced into an opening in the side of the tube in such a way that the air spins along the inside. As it does, the faster moving air molecules bump into the slower ones, pushing them out of the way, allowing the faster ones to collect and move along the wall.

A needle valve at the bottom of the tube bleeds off the faster moving molecules. The slower moving molecules, finding no way out, hit the bottom of the tube and form a small, central vortex heading back the other way. At the opposite end, they are bled off.

Here's the kicker. The hot air is really hot, and the cold, really cold. In a well-built vortex tube you can get -50 degree Fahrenheit air coming out of one end and 350 degree air out the other at the same time.

It requires no electricity or refrigerants and has no moving parts. It's just a specially shaped tube with a couple of valves. However, air has to be forced into it, so a fairly powerful compressor is required. (You don't get somethin' for nothin'.)

You can buy a small, ready-made vortex tube for about $150, but a handyman or woman could make a tube of their own for considerably less from materials available at a hardware store. The temperature difference created by a home-made tube wont be as dramatic as those stated above, but can still be impressive.

I saw one that, with an input air temperature of around 65 degrees F, provided -6 degrees out one end and 116 degrees out the other.

By adjusting the valve at the hot end, the temperature ratio of the two ends can be adjusted.

Here's my idea. Steal it if you want.

Picture a health club in which exercise bikes force air into vortex tubes. The hot air heats the place, and the cold refrigerates bottles of drinking water. In summer, cold air cools the place, and hot air cooks lunch and heats shower water.

I'm joking, of course. If such a large scale application were possible, Rudolf Hilsch would be doing handsprings in his grave. Vortex tubes are mainly used for spot cooling of tools in production machine shops.

Shops normally have compressed air anyway, so injecting some into vortex tubes to cool the cutting edge of tools is cleaner and more practical than using liquid cooling.

Though my health club idea is impractical, I'm still fascinated by vortex tubes. In fact, pardon me while I honor Monsieur Ranque and Herr Hilsch by stepping outside and shouting Wirbelrohr.