The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. It has no moving parts.
Pressurized gas is injected tangentially into a swirl chamber and accelerates to a high rate of rotation. Due to the conical nozzle at the end of the tube, only the outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex.
There are different explanations for the effect and there is debate on which explanation is best or correct.
What is usually agreed upon is that the air in the tube experiences mostly "solid body rotation", which simply means the rotation rate (angular velocity) of the inner gas is the same as that of the outer gas. This is different from what most consider standard vortex behaviour--where inner fluid spins at a higher rate than outer fluid. The (mostly) solid body rotation is probably due to the long time which each parcel of air remains in the vortex--allowing friction between the inner parcels and outer parcels to have a notable effect.
It is also usually agreed upon that there is a slight effect of hot air wanting to "rise" toward the center, but this effect is negligible--especially if turbulence is kept to a minimum.
One simple explanation is that the outer air is under higher pressure than the inner air (because of centrifugal force). Therefore the temperature of the outer air is higher than that of the inner air.
Another explanation is that as both vortices rotate at the same angular velocity and direction, the inner vortex has lost angular momentum. The decrease of angular momentum is transferred as kinetic energy to the outer vortex, resulting in separated flows of hot and cold gas.
This is somewhat analogous to a Peltier effect device, which uses electrical pressure (voltage) to move heat to one side of a dissimilar metal junction, causing the other side to grow cold.
When used to refrigerate, heat-sinking the whole vortex tube is helpful. Vortex tubes can also be cascaded. The cold (or hot) output of one can be used to pre-cool (or pre-heat) the air supply to another vortex tube. Cascaded tubes can be used, for example, to produce cryogenic temperatures.
How Vortex Tubes Work
How can you get cold air and hot air from one compressed-air stream? Lots of people have tried to explain it, including the French physicist who invented the Vortex Tube in the 1930's, Georges Ranque. Many different theories have been put forward.
Vortex Tubes behave in a very predictable and controllable way. When compressed air is released into the tube through the vortex generator, you get hot air out of one end of the tube and cold air out the other. A small valve in the hot end, adjustable with the handy control knob, lets you adjust the volume and temperature of air released from the cold end.
The vortex generator—an interchangeable, stationary part—regulates the volume of compressed air, allowing you to alter the air flows and temperature ranges you can produce with the tube.
"Cold Fraction": an important term for understanding Vortex Tube performance
"Cold Fraction" is the percentage of input compressed air that's released through the cold end of the tube. As a rule of thumb, the less cold air you release, the colder the air will be. You adjust the cold fraction with the control knob.
Cold fraction is also a function of the type of vortex generator that's in the tube, i.e., a "high cold fraction" or "low cold fraction" generator.
Most industrial process applications use a high cold fraction (above 50%). A high cold fraction tube can easily give you cold outputs 50-90°F (28-50°C) below your compressed air temperature.
High cold fractions give you a greater air flow, but they don't give the lowest possible temperatures. The high cold fraction combination of airflow and cold temperature produces the maximum refrigeration capacity, or greatest Btu/H (Kcal/H).
A low cold fraction (below 50%) means a smaller volume of air coming out that's very cold (down to -40°F/-40°C). In short, the less air you release, the colder the air.
Just remember, your maximum Btu/H (Kcal/H) capacity (also called maximum cooling or refrigeration) occurs with a high cold fraction tube.
Two tubes, ten levels of performance
AiRTX's modular design vortex tube gives you ten ranges of performance from a single tube, simply by changing the one-piece vortex generator. Both high and low cold-fraction generators are available for 8, 10, 15, 25 and 35 SCFM (220, 280, 420, 700, 990 SLPM) input flows. You can purchase vortex generators individually or in a kit that includes all sizes.
Other accessories include hot- and cold-end mufflers, air filters, regulators, thermostats and solenoid valves.
Vortex Tube Phenomenon
The vortex tube was discovered in 1930 by French physicist Georges Ranque. Vortec was the first company to develop this phenomenon into practical, effective cooling solutions for industrial applications. Here's how it works.
Fluid that rotates about an axis -- like a tornado -- is called a vortex. A vortex tube creates a vortex from compressed air and separates it into two air streams -- one hot and one cold. Compressed air enters a cylindrical generator which is proportionately larger than the hot (long) tube where it causes the air to rotate. Then, the rotating 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 exhaust. The remaining air is forced back through the center of the incoming air stream at a slower speed. The heat in the 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.
* Cool without refrigerants (CFCs/HCFCs) or moving parts for reliable, trouble- free operation.
* Use no electricity -- intrinsically safe, no RF interference.
* Compact and lightweight for easy installation -- even in tight areas.