The Vortex Tube, Maxwell’s Demon, Hilsch Tube, Ranque Tube: What Exactly is this Device? How Does it Work?

If I were to tell you that I can take a supply of ordinary compressed air and drop its temperature by 50°F with no moving parts and without any type of refrigerant or electrical connection, you might be scratching your head a bit. That is of course unless you’ve been introduced to the wild world of Vortex Tubes. My favorite product among the EXAIR Product Line, the Vortex Tube, does just that. With an ordinary supply of compressed air as the sole power source, and no moving parts, the Vortex Tube converts that airstream into a hot and cold flow that exits from opposite ends of the tube. No magic, witchcraft, or wizardry involved here. Just physics!

The theory all began in the 19th century with the famous physicist and mathematician James Clerk Maxwell. He suggested that since heat involves the movement of molecules, it could be possible to create a device that could distribute hot and cold air with no moving parts with the help of a “friendly little demon” that would sort and separate the hot and cold molecules of air. Not much was done with regard to this or any further advancement until about 61 years later.

In 1928, a French physics student by the name of George Ranque was conducting some testing on a vortex-type pump he had developed. In this testing, he noticed that warm air was exhausting from one end, while cold air was coming out of the other. He dropped his plans for the pump and begin an attempt to exploit this phenomenon commercially. His business ultimately failed, along with the Vortex Tube theory, until 1945 when a German physicist named Rudolph Hilsch published a scientific paper based on the Vortex Tube.

With so many involved, the tube became known by a variety of different names: “Ranque Vortex Tube”, the “Hilsch Tube”, the “Ranque-Hilsch Tube”, and (my personal favorite) “Maxwell’s Demon”. Over the years, it has gained a reputation as a low cost, reliable, and highly effective method for industrial spot cooling and panel cooling applications. While using the tube as a PC cooler isn’t generally recommended, here’s a great video demonstrating the tube in operation from Linus Tech Tips on YouTube:

So how exactly does this thing work? The truth is no one knows for certain, but there is one commonly accepted theory that explains the phenomenon:

Compressed air is supplied into the tube where it passes through a set of nozzles that are tangent to the internal counterbore. The design of the nozzles force the air to spin in a vortex motion at speeds up to 1,000,000 RPM. The spinning air turns 90° where a valve at one end allows some of the warmed air to escape. What does not escape, heads back down the tube in the inner stream where it loses heat and exhausts through the other end as cold air.

Both streams rotate in the same direction and at the same angular velocity. Due to the principle of conservation of angular momentum, the rotational speed of the inner vortex should increase. However that’s not the case with the Vortex Tube. The best way to illustrate this is in Olympic Figure Skating. As the skater is wider, the spinning motion is much slower. As she decreases her overall radius, the velocity picks up dramatically and she spins much quicker. In a Vortex Tube, the speed of the inner vortex remains the same as it has lost angular momentum. The energy that is lost in this process is given off in the form of heat that has exhausted from the hot side of the tube. This loss of heat allows the inner vortex to be cooled, where it can be ducted and applied for a variety of industrial applications.

This Vortex Tube theory is utilized in basic Vortex Tubes, along with a variety of other products that have additional features specific for your application. EXAIR’s line of Cabinet Coolers, Cold Guns, Adjustable Spot Coolers, Mini Coolers, and Vortex Tubes all operate off of this same principle.

If you’re fascinated by this product and want to give it a try, EXAIR offers an unconditional 30 day guarantee. We have them all in stock and ready to ship as well, same day with an order received by 2:00 ET. Feel free to get in contact with us if you’d like to discuss how a vortex-based product could help you in your processes.

Tyler Daniel, CCASS

Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

Vortex Tubes for Dummies

Vortex Tubes are intriguing. We can obtain such extreme cold or hot air with nothing more than compressed air and the Vortex Tube. We can adjust the temps very easily with the turn of a screw. Before we dive into how to adjust and get the right temps for your application, let me share a diagram of how the Vortex Tube works:

The unique physical phenomenon of the Vortex Tube principle generates cold air instantly, and for as long – or short – a time as needed.

Now that we have seen how it works, we need to define how to make it work for your specific application! First we need to set the cold fraction… Setting the “cold fraction” is all about how cold or hot you need the air to be. When we talk about this cold fraction, we are talking about the amount of the cold air that comes out of the cold side of the Vortex Tube, which also affects the temperature of that cold air. In other words, a 60% cold fraction equals 60% of the input compressed air exiting the Vortex Tubes cold side.

For example, if you are supplying 80 psi to our medium sized Vortex Tube, you will be generating between 10 and 40 SCFM (depending on the size of the generator). Let’s assume for this example that you are using our 3230 Vortex Tube, generating 30 SCFM. At an 80% cold fraction, 24 SCFM (80% of 30) will be flowing out of the cold end of the Vortex Tube. And it will be flowing at a temperature that is 50°F colder than the temperature of the compressed air provided. Yes, that is correct, assuming that your inlet air temp is 72°F, you will be flowing 24 SCFM of 22°F air from the cold end of the Vortex Tube. But what about the other 6 SCFM? Well, that will be flowing out of the hot end at a whopping 252°F. We must take into account both ends of the Vortex Tube. You can see the performance table below.

EXAIR Vortex Tube Performance Chart

Let’s look at one more example of this same Vortex Tube 3230. Let’s assume that we need to heat something up. Assuming that your compressed air is 72°F, and we want to heat something up to 115°F, we need to add 43°F to the temp of the compressed air. We can see in the chart that by supplying 80 psig of compressed air, and a 30% Cold Fraction on the Vortex Tube that we can add 43° to the temp of the air. We know that the cold end will give us 9 SCFM (30% of the overall 30 SCFM) and it will flow at -110°F, or -38°F. But we will reach our 115°F desired temp on the hot end, but that will only be at 21 SCFM. If we still need that higher SCFM, we may need to change the generator (explained below) or increase to a larger Vortex Tube all together.

As you can see from the above performance table, there are many ways to get to your desired temperature, be it hot or cold.

Adjusting the Vortex Tube

Next comes the question of how do we adjust the cold fraction. 1st, let me note that unless specified, these always ship to you set at or close to the 80% cold fraction, but, if you want them set to a precise cold fraction, we can permanently set these for you prior to shipping. As you see in the picture to the left, the slotted valve can be turned to adjust the cold fraction. For precision purposes it is always recommended to use a thermometer to set this where you need it (insert the thermometer into the cold flow of air). As a guide, you should seat the valve softly, and back off an 1/8th, a 1/4, or a 1/2 turn (for the small, medium, and large sizes respectively) to drop approximately 20% on the cold fraction scale.

We offer 3 sizes of Vortex Tubes, small, medium and large. Each size offers 3-5 different interchangeable size generators, with a total offering of 12 stock Vortex Tubes. The size of the generator will determine the BTU/hr, as well as the SCFM generated. See the following table for more details:

There are a few other key details to know about the Vortex Tubes. They do not like back pressure. As you can imagine, the magic that makes these work is spinning the generator inside. If that is slowed down due to back pressure, well, it will hinder the results of the entire Vortex Tube. Many people have air coolers or heaters on their compressed air system, keep in mind that the temps generated by the Vortex Tubes are ± the temperature of the compressed air, so it is important to know the temp of your compressed air.

Vortex Tubes can be very loud. We almost always sell these with the Cold and Hot Mufflers. In order to keep most of them under the OSHA standards for sound, you will want the mufflers. Lastly, as with all of EXAIR’s products, it is recommended to use a pressure regulator with a gauge at the point of use. With the Vortex Tubes, it is imperative if you are looking for an accurate temperature.

If you have any questions about the Vortex Tubes, or any of our intelligent air products, please do not hesitate to reach out.

Thank you for stopping by,

Brian Wages

Application Engineer

EXAIR Corporation
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Video Blog: Cabinet Cooler® System Calculator

In may I wrote a Blog Announcing our new Calculator tool on EXAIR.COM! You can read it here!

The Video below will walk you through how to get the information you need to fill the form in, and take you all the way to final where you can add it to your cart!

By providing certain information like size of the enclosure, NEMA rating needed, and environmental conditions, this new calculator will sort through our large selection of ready-to-ship Cabinet Cooler® Systems and provide instant feedback on the best model number for any applicable electrical enclosure.  Taking the guess work out of the equation, EXAIR’s Calculator ensures the customer that they can be confident in selecting the correct product for their unique specifications. You can even Print the form for your records!

If you have any questions or need additional support with the Sizing Calculator please reach out to one of our application Engineers give us a call. Or shoot us an email to techelp@exair.com

Jordan Shouse
Application Engineer

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Vortex Tubes Create Freeze Seals For Maintenance on Water Lines

Freeze plugs or Freeze seals are regularly used in nuclear reactor fluid systems to drain or isolate components that, for various reasons, cannot be conveniently isolated by valving. Once they are isolated, they are able to perform maintenance or upgrades without shutting down an entire system.

The United State Navy utilizes a large vortex tube to supply -50°F cooled air stream into a freeze jacket around the pipe. A time frame is chosen based on pipe size and fluid in the pipe to verify they are generating adequate cooling.  Temperature monitoring is put in place, flow through the pipe is stopped, and cooling of the freeze seal begins.  The water near the walls of the pipe freezes first.  Next, the frozen liquid continues towards the center until a solid plug of ice exists.  The freeze seal is then subcooled to a pre-determined temperature at which point the freeze is considered equivalent to a shut valve. Between the Ice plug and the small bit of pipe shrinkage at the point of cooling these seals are able to hold back thousands of pounds! (See drawing below, Shrinkage exaggerated for viewing)

Vortex Based Freeze Seal

In the attached photo bellow, (Provided by the U.S. Navy, photo by John Lenzo) this is a Freeze seal training Rig! You will see three colored lines, Blue is the cold air flow supplied by the vortex tube, red is the hot air from the vortex tube is exhausting away from the application location, and yellow is the pipe they are creating the freeze seal on. Surrounding that pipe is a jacket that holds the -50°F air in contact with the pipe.

With careful temperature monitoring in place and backup cooling methods on standby the work up stream can start.  Coolant flow throughout the rest of the system can now be reestablished.  Following the repair, flow will again be stopped for several hours while the freeze seal is given time to melt.  This ensures that the ice plug is not shot through the now repaired machine.

If you think you have an application that would benefit from Vortex tube technology, give us a call! We have a team of Application Engineers in from 7AM-4PM EST M-F! Or shoot us an email to techelp@exair.com and one of those Engineers will reach out to you!

Jordan Shouse
Application Engineer

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Freeze Seal Image Provided by the U.S. Navy