How Vortex Tubes Work

A vortex tube is an interesting device that has been looked upon with great fascination over the last 89 years since its discovery by George Ranque in 1928. What I’d like to do in this post is to give some insight into some of the physics of what is happening on the inside.

With a Vortex Tube, a high pressure compressed air stream id fed into a plenum chamber that contains a turbine-looking part called a generator. The generator serves to regulate flow and spin the air to create two separate streams. One hot and one cold.

Below is an animation of how a Vortex Tube works:

Function of a Vortex Tube

The generator also provides the pathway for the cold air to escape. This is where the cooled “inner vortex” passes through the generator to escape from the cold air outlet.

Vortex generator

Once the compressed air has moved through the generator, we have two spinning streams, the outer vortex and the inner vortex as mentioned above.  As the spinning air reaches the end of the hot tube, a portion of the air escapes past the control valve (the gold triangle in the animation above); and the remaining air is forced back through the center of the outer vortex.  This is what we call a “forced” vortex.

If we look at the inner vortex, this is where it gets interesting.  As the air turns back into the center, two things occur.  The two vortices are spinning at the same angular velocity and in the same rotational direction.  So, they are locked together.  But we have energy change as the air processes from the outer vortex to the inner vortex.

If we look at a particle that is spinning in the outer vortex and another particle spinning in the inner vortex, they will be rotating at the same speed.  But, because we lost some mass of air through the control valve on the hot end exhaust and the radius is decreased, the inner vortex loses angular momentum.

Angular momentum is expressed in Equation 1 as:

L = I * ω

L – angular momentum
I – inertia
ω – angular velocity

Where the inertia is calculated by Equation 2:

I = m * r2

m – mass
r – radius

So, if we estimate the inner vortex to have a radius that is 1/3 the size of the outer vortex,  the calculated change in inertia will be 1/9 of its original value.  With less mass and  a smaller radius, the Inertia is much smaller.  The energy that is lost for this change in momentum is given off as heat to the outside vortex.

Adjustments in output temperatures for a Vortex Tube are made by changing the cold fraction (with the control valve) and the input pressure.  The cold fraction is a term that we use to show the percentage of air that will come out the cold end.  The remaining amount will be exhausted through the hot end. You can call this the “hot fraction”, but since it is usually the smaller of the two flows and is rarely applied, we tend to focus on the cold end flow with the “cold fraction”.  The “Cold Fraction”  is determined by the control valve on the hot end of the Vortex Tube. The “Cold Fraction” chart below can be used to predict the difference in temperature drop in the cold air flow as well as the temperature rise in the hot air flow.

Vortex Tube Cold Fraction

By combining the temperature drops expressed above with the various flow rates in which Vortex Tubes are available, we can vary the amount of cooling power produced for an application. The above cold fraction chart was developed through much testing of the above described theory of operation. The cold fraction chart is a very useful tool that allows us to perform calculations to predict vortex tube performance under various conditions of input pressure and cold fraction settings.

The most interesting and useful part about vortex tube theory is that we have been able to harness this physical energy exchange inside a tube that can fit in the palm of your hand and which has a multitude of industrial uses from spot cooling sewing needles to freezing large pipes in marine applications to enable maintenance operations on valves to be performed.

We would love to entertain any questions you might have about vortex tubes, their uses and how EXAIR can help you.

Jordan Shouse
Application Engineer

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Custom Vortex Tubes by EXAIR

Vortex tube

EXAIR’s Vortex Tubes are a low-cost, reliable, and maintenance-free solution to a variety of industrial spot cooling problems. With just an ordinary supply of compressed air, the Vortex Tube produces two streams of air: one hot and one cold. This is achieved without any moving parts or refrigerants!!

The Vortex Tube is capable of achieving a temperature drop/rise from your compressed air supply ranging from -50°F to +260°F (-46°C to +127°C). Flow rates range from 1-150 SCFM (28-4,248 SLPM) and refrigeration of up to 10,200 Btu/hr. With all Vortex Tubes constructed of stainless steel, they’re resistant to corrosion and oxidation ensuring you years of reliable, maintenance-free operation.

How A Vortex Tube Works

In addition to providing a range of different Vortex Tubes available to ship same-day from stock, EXAIR also has a few options available for cases where a stock Vortex Tube may not be the right solution. The standard Vortex Tube is suitable for use in environments with ambient temperatures up to 125°F (52°C) due to the plastic generator and Buna o-rings. For more extreme environments and ambient temperatures up to 200°F (93°C), we install a brass generator and replace the Buna o-rings with Viton seals.

All standard Vortex Tubes are adjustable. A small valve is located at the hot air exhaust end of the tube. Using a flat-tipped screwdriver, you can adjust the amount of air that is permitted to exhaust from the hot end. As more air is allowed to escape, the temperature at the cold end of the tube drops even further. The volume of air at the cold end as the temperature drops will also decrease. The percentage of air exhausting from the cold end relative to the total air consumption is referred to as the cold fraction percentage. Lower cold fractions will produce lower temperatures, but there won’t be as much volume. Finding the proper setting for your Vortex Tube can take some adjusting.

HT3240

As we all know, if there’s a knob to turn, button to press, or adjustment that can be made an operator is inevitably going to tinker with it. Day shift will blame the night shift, night shift blames the day shift, and it can present a problem when the Vortex Tube has been specifically tested and set to achieve the desired cold fraction. If you know the cold fraction you need, but would prefer to prevent it from being able to be adjusted, EXAIR can install a precisely drilled hot plug to set the cold fraction percentage to your specifications and eliminate any potential for it to be changed.

If you’d still prefer to keep the adjustability, but don’t have the capabilities to measure and set it yourself, we can also set any Vortex Tube to the desired cold fraction with the adjustable valve and send it to you ready to be installed. We’ll provide you with a special model number so you can rest assured that any time you need another it’ll come set to your specification.

At EXAIR, we’re committed to providing you with the best solution possible for your application. Sometimes that isn’t going to be achievable with a standard stock product. Just because you don’t see it in the catalog or on our website, doesn’t mean we can’t do it. If you have a unique application and would like more information on getting a special Vortex Tube, contact an Application Engineer today.

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

How to Apply Vortex Tubes and Understand Cold Fractions

It’s been almost 100 years since Georges Ranque discovered the vortex tube phenomenon. Since then, they’ve become one of the best worst kept secrets in industry…I talk to callers all the time who have a piece of equipment that came with one of our Cabinet Cooler Systems installed, and they want to know how to get cold air like that for a machine tool cutting or spot cooling application. Other callers have discovered Vortex Tubes for the first time via a web search, or they saw one at a customer’s (or vendor’s) facility. They often sound like someone asking a magician to reveal the secret behind a trick. Of course, it’s not magic (not really) – but it is certainly a neat trick:

Then, the discussion turns to product selection. EXAIR Vortex Tubes come in three sizes, with multiple Models in each size range. Those different Models are all the same Small, Medium, or Large Vortex Tube, with a different Generator installed, which determines the amount of compressed air the Vortex Tube will consume…and the Cold Fraction range. These two variables go hand in hand when determining which Vortex Tube is right for the application.

‘Cold Fraction’ is the term for the percentage of the supply air that’s directed to the cold end. The higher the Cold Fraction, the higher the flow, and the temperature, of the cold air flow. Conversely, the lower the Cold Fraction, the lower the cold air flow…and temperature.

For jobs that call for rapid cooling to ambient temperature (or a little below), a “Max Refrigeration” Generator is installed in a 3200 Series Vortex Tube. They are designed to direct most of the compressed air flow to the cold end, exhausting a smaller amount out of the hot end. A Vortex Tube set at an 80% Cold Fraction is generally very close to being optimized for these applications: they’re putting out a decent amount of air flow, with a 54F temperature drop. Assuming the compressed air supply is roughly room temperature, that means you’re blowing 20 to 30F (-6.6 to -1.1C) air onto your part. Most of the time, it’ll cool it down in a real hurry. The final piece of the puzzle, then, is determining the cold air flow rate. Our lowest capacity Small Vortex Tube with a Max Refrigeration Generator will use 2 SCFM @100psig, and generates a flow of 1.6 SCFM of cold air. On the other end of the spectrum, our highest capacity Large Vortex Tube uses 150 SCFM @100psig, and gives you a cold flow of 120 SCFM. There are ten Models in between, so we can come quite close to an optimal selection for just about any size/shape of part that needs cooled.

Keep in mind that there are two variables in a convection/conduction air cooling application: the flow rate of the air, and the difference in temperature in the cooling air and the hot part. We’ll always recommend starting at the highest cold fraction, but you may find that a little bit lower flow…and the lower temperature that comes with it…might suit your needs better. Good news is, that doesn’t change the compressed air consumption, so you can optimize performance at no additional cost of operation.

Other applications call for air that’s just as cold as possible. For those, we offer our 3400 Series “Max Cold Temperature” Vortex Tubes. Where the 3200 Series’ Cold Fractions are adjustable from 50-80%, the 3400 Series can be adjusted from 20-50%. Assuming, again, that the compressed air supply is roughly room temperature, at a 20% Cold Fraction and 100psig supply pressure, your cold flow can be as low as -50F (-45.6C). If you’re trying to get something to a particularly low temperature – lab samples or circuits that need to be tested at a certain temperature, or freeze seals in piping systems, for instance – then a 3400 Series Vortex Tube is just what you’re looking for. These come in the same sizes & Models as the 3200 Series, from 2 to 150 SCFM.

Another nice thing about using a Vortex Tube for cold air is that you can turn them on and off as frequently (or as seldom) as needed. They’re generating cold air flow, at their published rated temperature, instantly. There are no moving parts to wear, so you can cycle them on and off rapidly, or let them run continuously. In fact, if you supply them with clean, moisture free air, they’ll run darn near indefinitely, maintenance free.

Here’s a short video, showing how to adjust the Cold Fraction of a Vortex Tube. If you’d like to find out more, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Have A Blast (Of Cold Air) With EXAIR Vortex Tubes & Spot Cooling Products

The operation of a Vortex Tube is one of the more peculiar phenomena in fluidics, and a particularly unique method of producing cold air. Since they don’t perform “heat transfer” in the classical sense (see below), there’s no RATE of heat transfer…they’re generating cold air, at rated flow and temperature, instantly.

Compressed air enters the Vortex Tube (blue arrow) where the Generator imparts a spinning motion to the flow, which continues towards the “hot end” (red ribbon). The flow is forced to change directions and continue spinning, flowing in the opposite direction (blue ribbon). It’s at this point that the flow gives up energy in the form of heat, which is exhausted through the Hot Valve (red arrows) while the cold flow makes its way to the opposite end, where it exits at temperatures up to 129F colder than the compressed air supply.

EXAIR Corporation’s Vortex Tubes come in a range of sizes & cooling capacities, and are integrated into a number of Spot Cooler Products which add convenience and flexibility to their operation. Consider:

  • Vortex Tubes themselves are perfect for the most basic of installations. Small and Medium models weigh only a few ounces; you can thread them directly onto an existing 1/8 NPT (Small) or 1/4 NPT (Medium) fitting, if you have one (or can get one) adjacent to where you want to blow the cold air. Hot and Cold Mufflers can be added for sound attenuation, and the Cold Caps have 1/4 NPT (Small) or 3/8 NPT (Medium) female threads if you want to use a short pipe or hose to direct the cold flow.
  • Most spot cooling applications are best handled with the higher air flows and moderate temperature drops associated with a Vortex Tube product set to a high cold fraction. We have three distinct products that have a pre-set, non-adjustable cold fraction, aimed at these situations:
    • Mini Cooler Systems are quiet, compact, and ready to install in minutes via a Swivel Magnetic Base. They’re ideal for cooling small tools, needles in industrial sewing machines, saw blades, or lens grinders, just to name a few of the more popular applications. These come with built-in hot muffler, and are available with a Single or Dual Outlet Cold Air Hose Kit.
    • For applications that call for a higher cooling capacity, we offer the Cold Gun Aircoolant Systems. These have a bar magnet built in to the Cold Gun itself, integral Hot and Cold Mufflers, and, like the Mini Coolers, come with Single or Dual Outlet Cold Air Hose Kits. They’re most popularly specified to replace mist coolant in machine tools, but are also used on routers, grinders, drills, larger saws, and even some non-machining applications like chill rolls and setting hot melt adhesives.
    • For even higher cooling capacities than that, the High Power Cold Gun can be used. Size-wise, it’s identical to the Cold Gun, but it generates twice the Cold Gun’s flow of cold air.
Mini Cooler (left) and Cold Gun (right).

One of the main advantages of using these Vortex Tube products with the pre-set higher cold fractions is the prevention of freeze-up…while the cold air generated is usually just a little below 32F (0C), ambient conditions in the areas where they’re used typically add enough heat to prevent mass freezing of any moisture condensed in the cooling process. A number of applications, however, do indeed call for much colder air flow than this, and for those, we’ve got the Adjustable Spot Cooler:

EXAIR Adjustable Spot Coolers can generate temperatures as low as -30°F (-34°C) instantly, and on demand.

Their versatility makes them a great “utility player” – when very cold air (well below zero) is needed, the Temperature Control Knob is turned counterclockwise. If another application calls for higher flow (like the Mini Coolers or Cold Guns), it can be turned clockwise for instant adjustment of flow and temperature.

Adjustable Spot Cooler Systems are available with Single or Dual Point Cold Air Hose Kits, and come with three Generators: 15 SCFM (installed), 25 SCFM, and 30 SCFM, to select the compressed air consumption, and hence, the overall flow range.

If you’ve got a spot cooling application, EXAIR Corporation has a Vortex Tube solution for you. Give me a call; let’s talk cold air!.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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