of serious scientific pursuit and the feeling of exploration was very high — especially with the scant direction.

In November 1958, Scientific American published one of my favorite projects — the Hilsch Vortex Tube. Invented in 1933 by a French physicist named George Ranque, and improved by a German physicist named Rudolf Hilsch in 1955, it uses nothing but compressed air. The design of the device created a vortex that acts as a demon to “split” the hot molecules from the cold by spinning air to very high speeds. How fast? Half a million rpm fast.

Spinning air is enough to generate a temperature change of a couple hundred degrees? Yes, but at the time of the original 1958 article, they weren’t exactly sure how it worked. As a very amateur scientist, I will try to explain the process. Compressed air is shot into a vortex that creates a hollow cyclone of fast, hot air that travels down the interior of the hot pipe. If it were visible, it would look like a tube of hot air that lines the inside of the pipe, and then a smidge of the hot air is exhausted through the almost-closed stopcock.

The remainder of the air is reflected off the nearly blocked stopcock through the center of the hot-air cyclone — in effect, a column of air shooting through the hot-air tube. As this happens, this column of air “gives up” its heat to the surrounding cyclone as it passes through the center. When the cold column reaches the vortex, it shoots through the center and exits the cold side. Whoa.

Cold-Cut-and-Soda-Pop Engineering

Anticipating a lukewarm response from my buddies for a “Let’s Build a Vortex Tube Party,” I invited my amateur scientist friends for a poker night (little did they know that “poker” was an acronym for Proof Of Koncept/Experimentation Revue).

Demon illustration by Mark Frauenfelder

Fearing a rebellion when they discovered there were no poker chips or one-eyed jacks, I made certain to lay out an impressive spread of top-notch cold cuts, provolone, olives, marinated pepperoncinis, and plonk chianti. I would have served a better wine, but I figured these wily characters would have realized they had been duped by my dodgy scheme, checked that their wallets were intact, and hit the door.

Original Mister Jalopy Proposal With a deep breath and steely resolve, I told the fellas that instead of a freewheeling night of gam-

A

^B

A

^B

A

^B

MAXWELL’S DEMON THOUGHT EXPERIMENT CIRCA 1867

1. Chambers A and B contain gas at equal temperature. The demon has the door closed but is ready to move quickly to let the molecules through.

2. As a fast/hot molecule approaches from chamber B, the demon throws open the door to admit the molecule to the soon-to-be-hotter chamber A.

3. Much door opening and closing ensues until the demon has tirelessly isolated all the cold from hot molecules.

Make: 35