Vortex Tubes: What, Why, Where?

The most common questions about Vortex Tubes are “How long have they been around?” and “How do they work?”. These questions are simple enough and answering someone how long Vortex Tubes have been around is the easy answer, Vortex Tubes have been around since 1928 with what may seem as an accidental existence by the developer George Ranque.

As to how they work, these are a phenomenon of physics and the theoretical math behind them has yet to be proven and set in stone. They have been called various names such as “Maxwell’s Demon” which posited that a demon was splitting the hot and cold air molecules prior to leaving the Vortex Tube.  They have also been referred to as  the “Ranque Vortex Tube”, “Hilsch Tube”, and the “Ranque-Hilsch Tube” which highlight some of the prominent people in developing vortex tubes. 

WHAT: EXAIR defines a Vortex Tube within our catalog as “a low cost, reliable, maintenance free solution to a variety of industrial spot cooling problems. Using an ordinary supply of compressed air as a power source, vortex tubes create two streams of air, one hot and one cold, with no moving parts.”

The scope of Vortex Tubes include being able to produce temperatures from -50 degrees to 260 degrees Fahrenheit with flow rates from 1 to 150 SCFM and refrigeration up to 10,200 Btu/hr. Temperatures, flows and cooling power can be easily adjusted with the control valve located on the “hot” end of the tube.

WHY: EXAIRs’ Vortex Tubes offer low cost and reliable solutions primarily for product cooling and sometimes heating. Constructed of stainless steel, our vortex tubes are resistant to corrosion and oxidation providing for years of reliable maintenance-free operation. Vortex tubes operate with a source of compressed air with no moving parts or electricity.

EXAIR offers two series of vortex tubes. The 32XX series is “Maximum Refrigeration (cooling) and is typically used for process cooling, part cooling or chamber cooling. The 34XX series provide lowest cold temperatures at low cold airflow and typically used in cooling lab samples and circuit testing.

EXAIR offers a cooling kit with interchangeable generators that are easily changed so you can experiment and find what temperature and airflow works best for your application.

WHERE: There are many uses for EXAIR Vortex Tubes including but not limited to cooling electronics, machining operations, CCTV cameras, soldered parts, gas samples, heat seals, environmental chambers, ultrasonic weld horns, welds and setting hot melts.

The history of EXAIR Vortex Tubes and the variety of uses has derived new products designed for specific applications like our Spot Coolers and Cabinet Coolers. These items can be found in our catalog or at www.EXAIR.com.

If you have any questions regarding these products or any products that EXAIR offers I hope to hear from you.

Eric Kuhnash
Application Engineer
E-mail: EricKuhnash@exair.com
Twitter: Twitter: @EXAIR_EK

How it Works: Theory Behind the Vortex Tube

What is a vortex tube and how does it work? A vortex tube is a device used to separate compressed air into a cold and hot stream of air; but the main question that many people have theorized is how does this device work.

In 1928 George Ranque, a French physics student stumbled upon this phenomenon on accident while he was performing experiments on a vortex type pump. During the experiment George noticed that hot air was being exhausted from one side and the other side was producing cold air. Eventually the device was forgotten about until 1945 when the German physicist, Rudolph Hilsch published a paper describing the device, eventually causing it to gain popularity and find applications in the industrial world.

EXAIR’s Vortex Tube uses compressed air as the supply and contains no moving parts to create a cold and hot stream of air from either end of the device. Using the valve located on the hot stream the vortex tube can achieve temperatures as low as -50°F (-46°C) and temperatures as high as 260°F (127°C).

The diagram bellow is one of the widely accepted explanations for the vortex tube phenomenon.

When the vortex tube is supplied with compressed air the air flow is directed into the generator that causes spin into a spiraling vortex at around 1,000,000 rpm. This spinning vortex flows down the neck of the hot tube denoted in the diagram as red. The control valve located on the end of the hot tube allows a fraction of the hot air to escape and what does not escape reverses direction and travels back down the tube in a second vortex denoted in blue. Inside of the low-pressure area of the larger outer warm air vortex, the inner vortex loses heat as it flows back to the front of the vortex and as it exits the vortex expels cold air.

The phenomenon is theorized to occur because both the hot and cold streams rotate at the same velocity and direction. This means that a particle of air in the inner vortex makes a complete revolution in the same time that a particle in the outer vortex takes to make a complete revolution. This effect is known as the principle of conservation of momentum and is the main driving force behind the vortex tube. In order for the system to stay in equilibrium air particles lose energy, in the form of heat, as they move from the outer stream to the inner stream, creating the cold air vortex that gets expelled.

At EXAIR we have harnessed many uses of vortex tubes for your cooling needs. Both our Cabinet Coolers and our Adjustable Spot Coolers utilize the vortex tube to either cool down an overheated cabinet or provide spot cooling for many different applications including to replace a messy coolant system for small grinding and machining applications.              

If you have questions about Vortex Tubes, or would like to talk about any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.   

Cody Biehle
Application Engineer
EXAIR Corporation
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Vortex Tube Cold Fractions Explained

Simply put, a Vortex Tube’s Cold Fraction is the percentage of its supply air that gets directed to the cold end. The rest of the supply air goes out the hot end. Here’s how it works:

The Control Valve is operated by a flat head screwdriver.

No matter what the Cold Fraction is set to, the air coming out the cold end will be lower in temperature, and the air exiting the hot end will be higher in temperature, than the compressed air supply.  The Cold Fraction is set by the position of the Control Valve.    Opening the Control Valve (turning counterclockwise, see blue arrow on photo to right) lowers the Cold Fraction, resulting in lower flow – and a large temperature drop – in the cold air discharge.  Closing the Control Valve (turning clockwise, see red arrow) increases the cold air flow, but results in a smaller temperature drop.  This adjustability is key to the Vortex Tube’s versatility.  Some applications call for higher flows; others call for very low temperatures…more on that in a minute, though.

The Cold Fraction can be set as low as 20% – meaning a small amount (20% to be exact) of the supply air is directed to the cold end, with a large temperature drop.  Conversely, you can set it as high as 80% – meaning most of the supply air goes to the cold end, but the temperature drop isn’t as high.  Our 3400 Series Vortex Tubes are for 20-50% Cold Fractions, and the 3200 Series are for 50-80% Cold Fractions.  Both extremes, and all points in between, are used, depending on the nature of the applications.  Here are some examples:

EXAIR 3400 Series Vortex Tubes, for air as low as -50°F.

A candy maker needed to cool chocolate that had been poured into small molds to make bite-sized, fun-shaped, confections.  Keeping the air flow low was critical…they wanted a nice, smooth surface, not rippled by a blast of air.  A pair of Model 3408 Small Vortex Tubes set to a 40% Cold Fraction produce a 3.2 SCFM cold flow (feels a lot like when you blow on a spoonful of hot soup to cool it down) that’s 110°F colder than the compressed air supply…or about -30°F.  It doesn’t disturb the surface, but cools & sets it in a hurry.  They could turn the Cold Fraction down all the way to 20%, for a cold flow of only 1.6 SCFM (just a whisper, really,) but with a 123°F temperature drop.

Welding and brazing are examples of applications where higher flows are advantageous.  The lower temperature drop doesn’t make all that much difference…turns out, when you’re blowing air onto metal that’s been recently melted, it doesn’t seem to matter much if the air is 20°F or -20°F, as long as there’s a LOT of it.  Our Medium Vortex Tubes are especially popular for this.  An ultrasonic weld that seals the end of a toothpaste tube, for example, is done with a Model 3215 set to an 80% Cold Fraction (12 SCFM of cold flow with a 54°F drop,) while brazing copper pipe fittings needs the higher flow of a Model 3230: the same 80% cold fraction makes 24 SCFM cold flow, with the same 54°F temperature drop.

Regardless of which model you choose, the temperature drop of the cold air flow is determined by only two factors: Cold Fraction setting, and compressed air supply pressure.  If you were wondering where I got all the figures above, they’re all from the Specification & Performance charts published in our catalog:

3200 Series are for max cooling (50-80% Cold Fractions;) 3400’s are for max cold temperature (20-50% Cold Fractions.)

Chocolate cooling in brown; welding/brazing in blue.

EXAIR Vortex Tubes & Spot Cooling Products are a quick & easy way to supply a reliable, controllable flow of cold air, on demand.  If you’d like to find out more, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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Georges J. Ranque and the Vortex Tube

The Vortex Tube was invented by accident in 1928, by George Ranque, a French physics student. He was performing experiments on a vortex-type pump that he had developed for vacuuming iron filings and noticed that warm air exhausted from one end and cold air from the other when he inserted a cone at one end of the tube! Ranque quickly stopped work on the pump, and started a company to take advantage of the commercial possibilities for this odd little device that produced both hot and cold air, using only compressed air, with no moving parts. The company was not successful, and the vortex tube was forgotten until 1945 when Rudolph Hilsch, a German physicist, published a widely read paper on the device.

How A Vortex Tube Works

A vortex tube uses compressed air as a power source, has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of the two air streams is adjustable with a valve built into the hot air exhaust.  Temperatures as low as -50°F (-46°C) and as high as 260°F (127°C) are possible.

During the second world war Georges J. Ranque started developing steels that would be used in military aviation efforts. After the war he took a job at  Aubert et Duval steelworks as director of metallurgical laboratory where he continued developing alloys for use in the aviation industry.

In 1972 he published a book on the search for the Philosophers stone, a legendary chemical substance capable of turning base metals such as mercury into gold. And in 1973 he passed away in his home just outside of Paris.

If you have any questions of want more information on how we use our vortex tubes to better processes all over industry. Give us a call, we have a team of application engineers  ready to answer your questions and recommend a solution for your applications.

Jordan Shouse
Application Engineer
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