Also see,
http://www.newmantools.com/vortex.htm#vortex
From link,
Operation
Any fluid that flows and rotates about an axis such as a tornado, is called a vortex. A vortex tube creates a vortex and separates it into two air streams-one hot and one cold. Figure 1 shows how a vortex tube works. Compressed air enters a cylindrical generator which is proportionately larger than the hot (long) tube. The generator causes the air to spiral. The spiraling air is forced down the inner walls of the hot tube at speeds reaching 1,000,000 rpm. At the end of the hot tube, a small portion of this air exits through a needle valve as hot air. The remaining air is forced back through the center of the incoming air stream but at a slower speed. The heat in slower moving air is transferred to the faster moving incoming air. This super-cooled air flows through the center of the generator and exits through the cold air exhaust port.
Temperature Separation Effects
The Vortex Tube Creates two types of vortices: free and forced. In a free vortex (like a whirlpool) the angular velocity of a fluid particle increases as it moves toward the Center of the vortex-that is, the closer a particle of fluid is to the center of a vortex, the faster it rotates. In a forced vortex, the velocity is directly, proportional to the radius of the vortex-the closer the center, the slower the velocity.
In a vortex tube, the outer (hot) air stream is a free vortex. The inner (cold) air stream is a forced vortex. The rotational movement of the forced vortex is controlled by the free vortex (hot air stream). The turbulence of both the hot and cold air streams cause the layers to be locked together in a single, rotational mass.
The inner air stream flows through the hollow core of the outer air stream at a slower velocity than the outer air stream. Since the energy is proportional to the square of the velocity, the cold air stream loses its energy by heat transfer. This allows energy to flow from the inner air stream to the outer air stream as heat creating a cold inner air stream.
Cold Fraction
The percentage of total input air volume released through the cold air exhaust of a Vortex Tube is called the Cold Fraction. A valve located in the hot air exhaust of the Vortex Tube controls the Cold Fraction. For example, if the total compressed air input is 15 SCFM (424.5 SLPM) and the Cold Fraction is 70%, the amount of air exiting the cold end wilt be 10.5 SCFM (297.2 SLPM); 4.5 SCFM (127.4 SLPM) exits the hot end.
Cold Fractions of 60-80% produce maximum efficiency-greatest power (BTUH) output- and are ideal for cooling machining operations, electrical controls and enclosures, liquid baths and workers. Low Cold Fractions (less than 50%) have reduced airflows and produce the lowest temperatures for cooling glass, laboratory experiments and for testing electronic components.